[PATCH v5 0/3] console/fbcon: Add support for deferred console takeover

Hi All,

Here is v5 of my patch-set, to delay fbcon taking over the console (and
binding to fbdev devices) until there actually is some text output to the
console. This is intended for use with the "quiet" cmdline option, in
combination with a bootloader which leaves the vendor's logo /
EFI bootgraphics put up by the firmware intact on the EFI framebuffer.

The end goal here is a boot where the firmware shows its boot graphics
and these stay in place for a couple of seconds until the GUI loads and
the GUI then smoothly takes over the framebuffer without any distruptions.

Bartlomiej, I believe that this patch-set is ready for merging now and
the first patch has Petr's ack, so can we get this merged now?

Also please create an inmutable (or topic) branch for this, so that the
drm people can merge it into drm-tip for additional testing.

Changelog:

Changes in v5:
-Improve commit message, explain why dummy_con.c is used to detect the
 first printout, instead of handling this entirely inside the fbcon code
 (no code changes, only updated the commit message)

Changes in v4:
-Keep the comments about which fbcon functions need locks in place

Changes in v3:
-Export is_console_locke() for use in modules (as fbcon may be built as a .ko)
-Use WARN_CONSOLE_UNLOCKED() in several places in the fbcon code to assert
 proper locking (requested by Daniel)
-Unregister the fbcon-dummycon-output-notifier on fbcon_exit() (req. by Daniel)
-Document the fbcon=nodefer commandline option (req. by Emil)

Changes in v2:
-Check the whole string when checking for erases in putcs, instead of just
 the first char
-Make dummycon_blank return 1, so that a redraw gets triggered and any text
 rendered while blanked gets output so that it can trigger a deferred
 takeover if one is pending

Regards,

Hans

This is a preparation patch for adding a number of WARN_CONSOLE_UNLOCKED()
calls to the fbcon code, which may be built as a module (event though
usually it is not).

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Sergey Senozhatsky <redacted>
Acked-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Daniel Vetter <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset
---
 kernel/printk/printk.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 247808333ba4..3f041e7cbfc9 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c

@@ -2243,6 +2243,7 @@ int is_console_locked(void)
 {
 	return console_locked;
 }
+EXPORT_SYMBOL(is_console_locked);
 
 /*
  * Check if we have any console that is capable of printing while cpu is

-- 
2.17.1

Currently fbcon claims fbdevs as soon as they are registered and takes over
the console as soon as the first fbdev gets registered.

This behavior is undesirable in cases where a smooth graphical bootup is
desired, in such cases we typically want the contents of the framebuffer
(typically a vendor logo) to stay in place as is.

The current solution for this problem (on embedded systems) is to not
enable fbcon.

This commit adds a new FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER config option,
which when enabled defers fbcon taking over the console from the dummy
console until the first text is displayed on the console. Together with the
"quiet" kernel commandline option, this allows fbcon to still be used
together with a smooth graphical bootup, having it take over the console as
soon as e.g. an error message is logged.

Note the choice to detect the first console output in the dummycon driver,
rather then handling this entirely inside the fbcon code, was made after
2 failed attempts to handle this entirely inside the fbcon code. The fbcon
code is woven quite tightly into the console code, making this to only
feasible option.

Reviewed-by: Daniel Vetter <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v2:
-Check the whole string when checking for erases in putcs, instead of just
 the first char
-Make dummycon_blank return 1, so that a redraw gets triggered and any text
 rendered while blanked gets output so that it can trigger a deferred
 takeover if one is pending

Changes in v3:
-Call WARN_CONSOLE_UNLOCKED() from fbcon_output_notifier()
-Unregister the notifier on fbcon_exit()
-Document the fbcon=nodefer commandline option in Documentation/fb/fbcon.txt

Changes in v5:
-Improve commit message, explain why dummy_con.c is used to detect the
 first printout, instead of handling this entirely inside the fbcon code
---
 Documentation/fb/fbcon.txt       |  7 ++++
 drivers/video/console/Kconfig    | 11 +++++
 drivers/video/console/dummycon.c | 67 +++++++++++++++++++++++++----
 drivers/video/fbdev/core/fbcon.c | 72 ++++++++++++++++++++++++++++++++
 include/linux/console.h          |  5 +++
 5 files changed, 154 insertions(+), 8 deletions(-)

diff --git a/Documentation/fb/fbcon.txt b/Documentation/fb/fbcon.txt
index 79c22d096bbc..d4d642e1ce9c 100644
--- a/Documentation/fb/fbcon.txt
+++ b/Documentation/fb/fbcon.txt

@@ -155,6 +155,13 @@ C. Boot options
 	used by text. By default, this area will be black. The 'color' value
 	is an integer number that depends on the framebuffer driver being used.
 
+6. fbcon=nodefer
+
+	If the kernel is compiled with deferred fbcon takeover support, normally
+	the framebuffer contents, left in place by the firmware/bootloader, will
+	be preserved until there actually is some text is output to the console.
+	This option causes fbcon to bind immediately to the fbdev device.
+
 C. Attaching, Detaching and Unloading
 
 Before going on how to attach, detach and unload the framebuffer console, an

diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig
index 4110ba7d7ca9..e91edef98633 100644
--- a/drivers/video/console/Kconfig
+++ b/drivers/video/console/Kconfig

@@ -150,6 +150,17 @@ config FRAMEBUFFER_CONSOLE_ROTATION
          such that other users of the framebuffer will remain normally
          oriented.
 
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+	bool "Framebuffer Console Deferred Takeover"
+	depends on FRAMEBUFFER_CONSOLE=y && DUMMY_CONSOLE=y
+	help
+	  If enabled this defers the framebuffer console taking over the
+	  console from the dummy console until the first text is displayed on
+	  the console. This is useful in combination with the "quiet" kernel
+	  commandline option to keep the framebuffer contents initially put up
+	  by the firmware in place, rather then replacing the contents with a
+	  black screen as soon as fbcon loads.
+
 config STI_CONSOLE
         bool "STI text console"
 	depends on PARISC && HAS_IOMEM

diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index f2eafe2ed980..45ad925ad5f8 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c

@@ -26,6 +26,65 @@
 #define DUMMY_ROWS	CONFIG_DUMMY_CONSOLE_ROWS
 #endif
 
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+/* These are both protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_output_nh);
+static bool dummycon_putc_called;
+
+void dummycon_register_output_notifier(struct notifier_block *nb)
+{
+	raw_notifier_chain_register(&dummycon_output_nh, nb);
+
+	if (dummycon_putc_called)
+		nb->notifier_call(nb, 0, NULL);
+}
+
+void dummycon_unregister_output_notifier(struct notifier_block *nb)
+{
+	raw_notifier_chain_unregister(&dummycon_output_nh, nb);
+}
+
+static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos)
+{
+	dummycon_putc_called = true;
+	raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
+}
+
+static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
+			   int count, int ypos, int xpos)
+{
+	int i;
+
+	if (!dummycon_putc_called) {
+		/* Ignore erases */
+		for (i = 0 ; i < count; i++) {
+			if (s[i] != vc->vc_video_erase_char)
+				break;
+		}
+		if (i = count)
+			return;
+
+		dummycon_putc_called = true;
+	}
+
+	raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
+}
+
+static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
+{
+	/* Redraw, so that we get putc(s) for output done while blanked */
+	return 1;
+}
+#else
+static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
+static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
+			   int count, int ypos, int xpos) { }
+static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
+{
+	return 0;
+}
+#endif
+
 static const char *dummycon_startup(void)
 {
     return "dummy device";

@@ -44,9 +103,6 @@ static void dummycon_init(struct vc_data *vc, int init)
 static void dummycon_deinit(struct vc_data *vc) { }
 static void dummycon_clear(struct vc_data *vc, int sy, int sx, int height,
 			   int width) { }
-static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos) { }
-static void dummycon_putcs(struct vc_data *vc, const unsigned short *s,
-			   int count, int ypos, int xpos) { }
 static void dummycon_cursor(struct vc_data *vc, int mode) { }
 
 static bool dummycon_scroll(struct vc_data *vc, unsigned int top,

@@ -61,11 +117,6 @@ static int dummycon_switch(struct vc_data *vc)
 	return 0;
 }
 
-static int dummycon_blank(struct vc_data *vc, int blank, int mode_switch)
-{
-	return 0;
-}
-
 static int dummycon_font_set(struct vc_data *vc, struct console_font *font,
 			     unsigned int flags)
 {

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index cd8d52a967aa..5fb156bdcf4e 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -129,6 +129,12 @@ static inline void fbcon_map_override(void)
 }
 #endif /* CONFIG_FRAMEBUFFER_CONSOLE_DETECT_PRIMARY */
 
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+static bool deferred_takeover = true;
+#else
+#define deferred_takeover false
+#endif
+
 /* font data */
 static char fontname[40];
 

@@ -499,6 +505,12 @@ static int __init fb_console_setup(char *this_opt)
 				margin_color = simple_strtoul(options, &options, 0);
 			continue;
 		}
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+		if (!strcmp(options, "nodefer")) {
+			deferred_takeover = false;
+			continue;
+		}
+#endif
 	}
 	return 1;
 }

@@ -3100,6 +3112,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 
 	WARN_CONSOLE_UNLOCKED();
 
+	if (deferred_takeover)
+		return 0;
+
 	idx = info->node;
 	for (i = first_fb_vc; i <= last_fb_vc; i++) {
 		if (con2fb_map[i] = idx)

@@ -3140,6 +3155,13 @@ static void fbcon_remap_all(int idx)
 
 	WARN_CONSOLE_UNLOCKED();
 
+	if (deferred_takeover) {
+		for (i = first_fb_vc; i <= last_fb_vc; i++)
+			con2fb_map_boot[i] = idx;
+		fbcon_map_override();
+		return;
+	}
+
 	for (i = first_fb_vc; i <= last_fb_vc; i++)
 		set_con2fb_map(i, idx, 0);
 

@@ -3191,6 +3213,11 @@ static int fbcon_fb_registered(struct fb_info *info)
 	idx = info->node;
 	fbcon_select_primary(info);
 
+	if (deferred_takeover) {
+		pr_info("fbcon: Deferring console take-over\n");
+		return 0;
+	}
+
 	if (info_idx = -1) {
 		for (i = first_fb_vc; i <= last_fb_vc; i++) {
 			if (con2fb_map_boot[i] = idx) {

@@ -3566,8 +3593,46 @@ static int fbcon_init_device(void)
 	return 0;
 }
 
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+static struct notifier_block fbcon_output_nb;
+
+static int fbcon_output_notifier(struct notifier_block *nb,
+				 unsigned long action, void *data)
+{
+	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
+	pr_info("fbcon: Taking over console\n");
+
+	dummycon_unregister_output_notifier(&fbcon_output_nb);
+	deferred_takeover = false;
+	logo_shown = FBCON_LOGO_DONTSHOW;
+
+	for (i = 0; i < FB_MAX; i++) {
+		if (registered_fb[i])
+			fbcon_fb_registered(registered_fb[i]);
+	}
+
+	return NOTIFY_OK;
+}
+
+static void fbcon_register_output_notifier(void)
+{
+	fbcon_output_nb.notifier_call = fbcon_output_notifier;
+	dummycon_register_output_notifier(&fbcon_output_nb);
+}
+#else
+static inline void fbcon_register_output_notifier(void) {}
+#endif
+
 static void fbcon_start(void)
 {
+	if (deferred_takeover) {
+		fbcon_register_output_notifier();
+		return;
+	}
+
 	if (num_registered_fb) {
 		int i;
 

@@ -3594,6 +3659,13 @@ static void fbcon_exit(void)
 	if (fbcon_has_exited)
 		return;
 
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+	if (deferred_takeover) {
+		dummycon_unregister_output_notifier(&fbcon_output_nb);
+		deferred_takeover = false;
+	}
+#endif
+
 	kfree((void *)softback_buf);
 	softback_buf = 0UL;
 

diff --git a/include/linux/console.h b/include/linux/console.h
index dfd6b0e97855..f59f3dbca65c 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h

@@ -21,6 +21,7 @@ struct console_font_op;
 struct console_font;
 struct module;
 struct tty_struct;
+struct notifier_block;
 
 /*
  * this is what the terminal answers to a ESC-Z or csi0c query.

@@ -220,4 +221,8 @@ static inline bool vgacon_text_force(void) { return false; }
 
 extern void console_init(void);
 
+/* For deferred console takeover */
+void dummycon_register_output_notifier(struct notifier_block *nb);
+void dummycon_unregister_output_notifier(struct notifier_block *nb);
+
 #endif /* _LINUX_CONSOLE_H */

-- 
2.17.1

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
 drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
 	struct fb_info *oldinfo = NULL;
  	int found, err = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (oldidx = newidx)
 		return 0;
 

@@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
 {
 	int i, new_idx = -1, ret = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!fbcon_has_console_bind)
 		return 0;
 

@@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 {
 	int i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	for (i = first_fb_vc; i <= last_fb_vc; i++) {
 		if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 static void fbcon_remap_all(int idx)
 {
 	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
 	for (i = first_fb_vc; i <= last_fb_vc; i++)
 		set_con2fb_map(i, idx, 0);
 

@@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
 {
 	int ret = 0, i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	fbcon_select_primary(info);
 

-- 
2.17.1

On Thursday, June 28, 2018 11:03:48 AM Hans de Goede wrote:

Hi All,

Here is v5 of my patch-set, to delay fbcon taking over the console (and
binding to fbdev devices) until there actually is some text output to the
console. This is intended for use with the "quiet" cmdline option, in
combination with a bootloader which leaves the vendor's logo /
EFI bootgraphics put up by the firmware intact on the EFI framebuffer.

The end goal here is a boot where the firmware shows its boot graphics
and these stay in place for a couple of seconds until the GUI loads and
the GUI then smoothly takes over the framebuffer without any distruptions.

Bartlomiej, I believe that this patch-set is ready for merging now and
the first patch has Petr's ack, so can we get this merged now?

Done, thanks for patches (also for reviews & acks).

Also please create an inmutable (or topic) branch for this, so that the
drm people can merge it into drm-tip for additional testing.

Daniel,

The following changes since commit 7daf201d7fe8334e2d2364d4e8ed3394ec9af819:

  Linux 4.18-rc2 (2018-06-24 20:54:29 +0800)

are available in the git repository at:

  https://github.com/bzolnier/linux.git tags/ib-fbdev-drm-v4.19-deferred-console-takeover

for you to fetch changes up to 83d83bebf40132e2d55ec58af666713cc76f9764:

  console/fbcon: Add support for deferred console takeover (2018-06-28 15:20:30 +0200)

----------------------------------------------------------------
Immutable branch between fbdev and drm for the v4.19 merge window
(contains the deferred console takeover feature)

----------------------------------------------------------------
Hans de Goede (3):
      printk: Export is_console_locked
      fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable
      console/fbcon: Add support for deferred console takeover

 Documentation/fb/fbcon.txt       |  7 ++++
 drivers/video/console/Kconfig    | 11 ++++++
 drivers/video/console/dummycon.c | 67 ++++++++++++++++++++++++++++----
 drivers/video/fbdev/core/fbcon.c | 83 ++++++++++++++++++++++++++++++++++++++++
 include/linux/console.h          |  5 +++
 kernel/printk/printk.c           |  1 +
 6 files changed, 166 insertions(+), 8 deletions(-)

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

HI,

On 28-06-18 15:50, Bartlomiej Zolnierkiewicz wrote:

On Thursday, June 28, 2018 11:03:48 AM Hans de Goede wrote:

quoted

Hi All,

Here is v5 of my patch-set, to delay fbcon taking over the console (and
binding to fbdev devices) until there actually is some text output to the
console. This is intended for use with the "quiet" cmdline option, in
combination with a bootloader which leaves the vendor's logo /
EFI bootgraphics put up by the firmware intact on the EFI framebuffer.

The end goal here is a boot where the firmware shows its boot graphics
and these stay in place for a couple of seconds until the GUI loads and
the GUI then smoothly takes over the framebuffer without any distruptions.

Bartlomiej, I believe that this patch-set is ready for merging now and
the first patch has Petr's ack, so can we get this merged now?

Done, thanks for patches (also for reviews & acks).

You're welcome and thank you for merging these.

Regards,

Hans

quoted

Also please create an inmutable (or topic) branch for this, so that the
drm people can merge it into drm-tip for additional testing.

Daniel,

The following changes since commit 7daf201d7fe8334e2d2364d4e8ed3394ec9af819:

   Linux 4.18-rc2 (2018-06-24 20:54:29 +0800)

are available in the git repository at:

   https://github.com/bzolnier/linux.git tags/ib-fbdev-drm-v4.19-deferred-console-takeover

for you to fetch changes up to 83d83bebf40132e2d55ec58af666713cc76f9764:

   console/fbcon: Add support for deferred console takeover (2018-06-28 15:20:30 +0200)

----------------------------------------------------------------
Immutable branch between fbdev and drm for the v4.19 merge window
(contains the deferred console takeover feature)

----------------------------------------------------------------
Hans de Goede (3):
       printk: Export is_console_locked
       fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable
       console/fbcon: Add support for deferred console takeover

  Documentation/fb/fbcon.txt       |  7 ++++
  drivers/video/console/Kconfig    | 11 ++++++
  drivers/video/console/dummycon.c | 67 ++++++++++++++++++++++++++++----
  drivers/video/fbdev/core/fbcon.c | 83 ++++++++++++++++++++++++++++++++++++++++
  include/linux/console.h          |  5 +++
  kernel/printk/printk.c           |  1 +
  6 files changed, 166 insertions(+), 8 deletions(-)

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

Hi Bartlomiej,

On Thu, 2018-06-28 at 15:50 +0200, Bartlomiej Zolnierkiewicz wrote:

On Thursday, June 28, 2018 11:03:48 AM Hans de Goede wrote:

quoted

Hi All,

Here is v5 of my patch-set, to delay fbcon taking over the console
(and
binding to fbdev devices) until there actually is some text output
to the
console. This is intended for use with the "quiet" cmdline option,
in
combination with a bootloader which leaves the vendor's logo /
EFI bootgraphics put up by the firmware intact on the EFI
framebuffer.

The end goal here is a boot where the firmware shows its boot
graphics
and these stay in place for a couple of seconds until the GUI loads
and
the GUI then smoothly takes over the framebuffer without any
distruptions.

Bartlomiej, I believe that this patch-set is ready for merging now
and
the first patch has Petr's ack, so can we get this merged now?

Done, thanks for patches (also for reviews & acks).

quoted

Also please create an inmutable (or topic) branch for this, so that
the
drm people can merge it into drm-tip for additional testing.

Daniel,

The following changes since commit
7daf201d7fe8334e2d2364d4e8ed3394ec9af819:

  Linux 4.18-rc2 (2018-06-24 20:54:29 +0800)

are available in the git repository at:

  https://github.com/bzolnier/linux.git tags/ib-fbdev-drm-v4.19-
deferred-console-takeover

for you to fetch changes up to
83d83bebf40132e2d55ec58af666713cc76f9764:

  console/fbcon: Add support for deferred console takeover (2018-06-
28 15:20:30 +0200)

----------------------------------------------------------------
Immutable branch between fbdev and drm for the v4.19 merge window
(contains the deferred console takeover feature)

----------------------------------------------------------------
Hans de Goede (3):
      printk: Export is_console_locked
      fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable
      console/fbcon: Add support for deferred console takeover

 Documentation/fb/fbcon.txt       |  7 ++++
 drivers/video/console/Kconfig    | 11 ++++++
 drivers/video/console/dummycon.c | 67 ++++++++++++++++++++++++++++
----
 drivers/video/fbdev/core/fbcon.c | 83
++++++++++++++++++++++++++++++++++++++++
 include/linux/console.h          |  5 +++
 kernel/printk/printk.c           |  1 +
 6 files changed, 166 insertions(+), 8 deletions(-)

Pulled into drm-misc-next, thanks

Gustavo

Hi Gustavo,

On Thursday, June 28, 2018 07:44:38 PM Gustavo Padovan wrote:

Hi Bartlomiej,

On Thu, 2018-06-28 at 15:50 +0200, Bartlomiej Zolnierkiewicz wrote:

quoted

On Thursday, June 28, 2018 11:03:48 AM Hans de Goede wrote:

quoted

Hi All,

Here is v5 of my patch-set, to delay fbcon taking over the console
(and
binding to fbdev devices) until there actually is some text output
to the
console. This is intended for use with the "quiet" cmdline option,
in
combination with a bootloader which leaves the vendor's logo /
EFI bootgraphics put up by the firmware intact on the EFI
framebuffer.

The end goal here is a boot where the firmware shows its boot
graphics
and these stay in place for a couple of seconds until the GUI loads
and
the GUI then smoothly takes over the framebuffer without any
distruptions.

Bartlomiej, I believe that this patch-set is ready for merging now
and
the first patch has Petr's ack, so can we get this merged now?

Done, thanks for patches (also for reviews & acks).

quoted

Also please create an inmutable (or topic) branch for this, so that
the
drm people can merge it into drm-tip for additional testing.

Daniel,

The following changes since commit
7daf201d7fe8334e2d2364d4e8ed3394ec9af819:

  Linux 4.18-rc2 (2018-06-24 20:54:29 +0800)

are available in the git repository at:

  https://github.com/bzolnier/linux.git tags/ib-fbdev-drm-v4.19-
deferred-console-takeover

for you to fetch changes up to
83d83bebf40132e2d55ec58af666713cc76f9764:

  console/fbcon: Add support for deferred console takeover (2018-06-
28 15:20:30 +0200)

----------------------------------------------------------------
Immutable branch between fbdev and drm for the v4.19 merge window
(contains the deferred console takeover feature)

----------------------------------------------------------------
Hans de Goede (3):
      printk: Export is_console_locked
      fbcon: Call WARN_CONSOLE_UNLOCKED() where applicable
      console/fbcon: Add support for deferred console takeover

 Documentation/fb/fbcon.txt       |  7 ++++
 drivers/video/console/Kconfig    | 11 ++++++
 drivers/video/console/dummycon.c | 67 ++++++++++++++++++++++++++++
----
 drivers/video/fbdev/core/fbcon.c | 83
++++++++++++++++++++++++++++++++++++++++
 include/linux/console.h          |  5 +++
 kernel/printk/printk.c           |  1 +
 6 files changed, 166 insertions(+), 8 deletions(-)

Pulled into drm-misc-next, thanks

Please also apply fixup branch:

The following changes since commit 83d83bebf40132e2d55ec58af666713cc76f9764:

  console/fbcon: Add support for deferred console takeover (2018-06-28 15:20:30 +0200)

are available in the git repository at:

  https://github.com/bzolnier/linux.git tags/ib-fbdev-drm-v4.19-deferred-console-takeover-fixup

for you to fetch changes up to 334bb8972a131e604a741e9b284d8867190c723e:

  console: dummycon: export dummycon_[un]register_output_notifier (2018-06-29 11:46:19 +0200)

----------------------------------------------------------------
Immutable branch between fbdev and drm for the v4.19 merge window
(contains build fixup for the deferred console takeover feature)

----------------------------------------------------------------
Hans de Goede (1):
      console: dummycon: export dummycon_[un]register_output_notifier

 drivers/video/console/dummycon.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
index 45ad925..0254251 100644
--- a/drivers/video/console/dummycon.c
+++ b/drivers/video/console/dummycon.c

@@ -38,11 +38,13 @@ void dummycon_register_output_notifier(struct notifier_block *nb)
 	if (dummycon_putc_called)
 		nb->notifier_call(nb, 0, NULL);
 }
+EXPORT_SYMBOL_GPL(dummycon_register_output_notifier);
 
 void dummycon_unregister_output_notifier(struct notifier_block *nb)
 {
 	raw_notifier_chain_unregister(&dummycon_output_nh, nb);
 }
+EXPORT_SYMBOL_GPL(dummycon_unregister_output_notifier);
 
 static void dummycon_putc(struct vc_data *vc, int c, int ypos, int xpos)
 {

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

On Fri, 2018-06-29 at 12:08 +0200, Bartlomiej Zolnierkiewicz wrote:

Pulled. Thanks.

Gustavo

On (06/28/18 11:03), Hans de Goede wrote:
[..]

 
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+	bool "Framebuffer Console Deferred Takeover"
+	depends on FRAMEBUFFER_CONSOLE=y && DUMMY_CONSOLE=y

+	default n

+	help
+	  If enabled this defers the framebuffer console taking over the
+	  console from the dummy console until the first text is displayed on
+	  the console. This is useful in combination with the "quiet" kernel
+	  commandline option to keep the framebuffer contents initially put up
+	  by the firmware in place, rather then replacing the contents with a
+	  black screen as soon as fbcon loads.

Can we please default this to 'n'?

	-ss

On Wed, 4 Jul 2018 01:13:27 +0900
Sergey Senozhatsky [off-list ref] wrote:

On (06/28/18 11:03), Hans de Goede wrote:
[..]

quoted

 
+config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+	bool "Framebuffer Console Deferred Takeover"
+	depends on FRAMEBUFFER_CONSOLE=y && DUMMY_CONSOLE=y  

+	default n

quoted

+	help
+	  If enabled this defers the framebuffer console taking over the
+	  console from the dummy console until the first text is displayed on
+	  the console. This is useful in combination with the "quiet" kernel
+	  commandline option to keep the framebuffer contents initially put up
+	  by the firmware in place, rather then replacing the contents with a
+	  black screen as soon as fbcon loads.  

Can we please default this to 'n'?

No explicit default means 'n'. You don't need to specify it.

-- Steve

On (07/03/18 12:14), Steven Rostedt wrote:

quoted

Can we please default this to 'n'?

No explicit default means 'n'. You don't need to specify it.

Ah, OK. Thanks.

	-ss

Hi

Am 28.06.2018 um 11:03 schrieb Hans de Goede:

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.

Debugging fbcon sometimes requires to not take the console lock. This
patch breaks the debugging workaround provided by
'fb.lockless_register_fb'. The dmesg is now filled with warnings about
the missing lock.

Best regards
Thomas

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstr. 5, D-90409 Nürnberg
Tel: +49-911-74053-0; Fax: +49-911-7417755;  https://www.suse.com/
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard,
Graham Norton, HRB 21284 (AG Nürnberg)

On Wed, 11 Jul 2018 16:46:11 +0200
Thomas Zimmermann [off-list ref] wrote:

Hi

Am 28.06.2018 um 11:03 schrieb Hans de Goede:

quoted

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.  

Debugging fbcon sometimes requires to not take the console lock. This
patch breaks the debugging workaround provided by
'fb.lockless_register_fb'. The dmesg is now filled with warnings about
the missing lock.

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

#define WARN_FB_CONSOLE_UNLOCKED() 			\
	do {						\
		if (unlikely(!lockless_register_fb))	\
			WARN_CONSOLE_UNLOCKED();	\
	} while (0)

And use that instead?

-- Steve

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
 drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
 	struct fb_info *oldinfo = NULL;
  	int found, err = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (oldidx = newidx)
 		return 0;
 

@@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
 {
 	int i, new_idx = -1, ret = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!fbcon_has_console_bind)
 		return 0;
 

@@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 {
 	int i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	for (i = first_fb_vc; i <= last_fb_vc; i++) {
 		if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 static void fbcon_remap_all(int idx)
 {
 	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
 	for (i = first_fb_vc; i <= last_fb_vc; i++)
 		set_con2fb_map(i, idx, 0);
 

@@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
 {
 	int ret = 0, i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	fbcon_select_primary(info);
   

Hi,

On 11-07-18 16:52, Steven Rostedt wrote:

On Wed, 11 Jul 2018 16:46:11 +0200
Thomas Zimmermann [off-list ref] wrote:

quoted

Hi

Am 28.06.2018 um 11:03 schrieb Hans de Goede:

quoted

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.

Debugging fbcon sometimes requires to not take the console lock. This
patch breaks the debugging workaround provided by
'fb.lockless_register_fb'. The dmesg is now filled with warnings about
the missing lock.

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

#define WARN_FB_CONSOLE_UNLOCKED() 			\
	do {						\
		if (unlikely(!lockless_register_fb))	\
			WARN_CONSOLE_UNLOCKED();	\
	} while (0)

And use that instead?

Yes I'm already preparing a patch like that :)

Without the unlikely though, this is not used in hot paths.

Regards,

Hans

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
  drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
  	struct fb_info *oldinfo = NULL;
   	int found, err = 0;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	if (oldidx = newidx)
  		return 0;
  

@@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
  {
  	int i, new_idx = -1, ret = 0;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	if (!fbcon_has_console_bind)
  		return 0;
  

@@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
  {
  	int i, idx;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	idx = info->node;
  	for (i = first_fb_vc; i <= last_fb_vc; i++) {
  		if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
  static void fbcon_remap_all(int idx)
  {
  	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
  	for (i = first_fb_vc; i <= last_fb_vc; i++)
  		set_con2fb_map(i, idx, 0);
  

@@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
  {
  	int ret = 0, i, idx;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	idx = info->node;
  	fbcon_select_primary(info);
    

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
...' construct [1]. I thought about turning this into a config option.

Best regards
Thomas

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203

#define WARN_FB_CONSOLE_UNLOCKED() 			\
	do {						\
		if (unlikely(!lockless_register_fb))	\
			WARN_CONSOLE_UNLOCKED();	\
	} while (0)

And use that instead?

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
 drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
 	struct fb_info *oldinfo = NULL;
  	int found, err = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (oldidx == newidx)
 		return 0;
 

@@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
 {
 	int i, new_idx = -1, ret = 0;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	if (!fbcon_has_console_bind)
 		return 0;
 

@@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 {
 	int i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	for (i = first_fb_vc; i <= last_fb_vc; i++) {
 		if (con2fb_map[i] == idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
 static void fbcon_remap_all(int idx)
 {
 	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
 	for (i = first_fb_vc; i <= last_fb_vc; i++)
 		set_con2fb_map(i, idx, 0);
 

@@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
 {
 	int ret = 0, i, idx;
 
+	WARN_CONSOLE_UNLOCKED();
+
 	idx = info->node;
 	fbcon_select_primary(info);
   

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstr. 5, D-90409 Nürnberg
Tel: +49-911-74053-0; Fax: +49-911-7417755;  https://www.suse.com/
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard,
Graham Norton, HRB 21284 (AG Nürnberg)

On Wed, Jul 11, 2018 at 5:01 PM, Hans de Goede [off-list ref] wrote:

Hi,

On 11-07-18 16:52, Steven Rostedt wrote:

quoted

On Wed, 11 Jul 2018 16:46:11 +0200
Thomas Zimmermann [off-list ref] wrote:

quoted

Hi

Am 28.06.2018 um 11:03 schrieb Hans de Goede:

quoted

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.

Debugging fbcon sometimes requires to not take the console lock. This
patch breaks the debugging workaround provided by
'fb.lockless_register_fb'. The dmesg is now filled with warnings about
the missing lock.

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

#define WARN_FB_CONSOLE_UNLOCKED()                      \
        do {                                            \
                if (unlikely(!lockless_register_fb))    \
                        WARN_CONSOLE_UNLOCKED();        \
        } while (0)

And use that instead?

Yes I'm already preparing a patch like that :)

Without the unlikely though, this is not used in hot paths.

Note that you don't even need an EXPORT_SYMBOL since this is all in
the same module.
-Daniel

Regards,

Hans

quoted

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
  drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c

b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int

user)
        struct fb_info *oldinfo = NULL;
        int found, err = 0;
  +     WARN_CONSOLE_UNLOCKED();
+
        if (oldidx = newidx)
                return 0;
  @@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
  {
        int i, new_idx = -1, ret = 0;
  +     WARN_CONSOLE_UNLOCKED();
+
        if (!fbcon_has_console_bind)
                return 0;
  @@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info
*info)
  {
        int i, idx;
  +     WARN_CONSOLE_UNLOCKED();
+
        idx = info->node;
        for (i = first_fb_vc; i <= last_fb_vc; i++) {
                if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info

*info)
  static void fbcon_remap_all(int idx)
  {
        int i;
+
+       WARN_CONSOLE_UNLOCKED();
+
        for (i = first_fb_vc; i <= last_fb_vc; i++)
                set_con2fb_map(i, idx, 0);
  @@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info
*info)
  {
        int ret = 0, i, idx;
  +     WARN_CONSOLE_UNLOCKED();
+
        idx = info->node;
        fbcon_select_primary(info);

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Hi,

On 11-07-18 17:07, Thomas Zimmermann wrote:

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

quoted

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

Hmm, so this option is already broken (in a way) then, my first reaction
to your mail was that we should just remove that option. But that seemed
a bit harsh to me so I've been working on a fix for the last 10 minutes
or so.

But if it is already broken I'm tempted to just remove the option and
be done with it.  We really need less cruft in the fbdev/fbcon code not
more.

WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
...' construct [1]. I thought about turning this into a config option.

Ah I noticed the #if but I did not notice that it was a "#if 1".

If you want to fix lockless_register_fb it really should be replaced
with a runtime check, not a Kconfig option. This would require having
some lockless variable in the console code itself, which then gets
set by the fbdev code during init based on its lockless_register_fb
setting.

But as said I think we should seriously consider just removing
lockless_register_fb.

Regards,

Hans

Best regards
Thomas

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203

quoted

#define WARN_FB_CONSOLE_UNLOCKED() 			\
	do {						\
		if (unlikely(!lockless_register_fb))	\
			WARN_CONSOLE_UNLOCKED();	\
	} while (0)

And use that instead?

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
  drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int user)
  	struct fb_info *oldinfo = NULL;
   	int found, err = 0;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	if (oldidx = newidx)
  		return 0;
  

@@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
  {
  	int i, new_idx = -1, ret = 0;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	if (!fbcon_has_console_bind)
  		return 0;
  

@@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info *info)
  {
  	int i, idx;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	idx = info->node;
  	for (i = first_fb_vc; i <= last_fb_vc; i++) {
  		if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info *info)
  static void fbcon_remap_all(int idx)
  {
  	int i;
+
+	WARN_CONSOLE_UNLOCKED();
+
  	for (i = first_fb_vc; i <= last_fb_vc; i++)
  		set_con2fb_map(i, idx, 0);
  

@@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info *info)
  {
  	int ret = 0, i, idx;
  
+	WARN_CONSOLE_UNLOCKED();
+
  	idx = info->node;
  	fbcon_select_primary(info);
    

On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede [off-list ref] wrote:

Hi,

On 11-07-18 17:07, Thomas Zimmermann wrote:

quoted

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

quoted

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

Hmm, so this option is already broken (in a way) then, my first reaction
to your mail was that we should just remove that option. But that seemed
a bit harsh to me so I've been working on a fix for the last 10 minutes
or so.

But if it is already broken I'm tempted to just remove the option and
be done with it.  We really need less cruft in the fbdev/fbcon code not
more.

Please don't remove it, it makes debugging kms driver issues on
initial modeset (which is usually run from framebuffer_register, while
hodling the console_lock) impossible.
-Daniel

quoted

WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
...' construct [1]. I thought about turning this into a config option.

Ah I noticed the #if but I did not notice that it was a "#if 1".

If you want to fix lockless_register_fb it really should be replaced
with a runtime check, not a Kconfig option. This would require having
some lockless variable in the console code itself, which then gets
set by the fbdev code during init based on its lockless_register_fb
setting.

But as said I think we should seriously consider just removing
lockless_register_fb.

Regards,

Hans

quoted

Best regards
Thomas

[1]

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203

quoted

#define WARN_FB_CONSOLE_UNLOCKED()                      \
        do {                                            \
                if (unlikely(!lockless_register_fb))    \
                        WARN_CONSOLE_UNLOCKED();        \
        } while (0)

And use that instead?

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
  drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c

b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int

user)
        struct fb_info *oldinfo = NULL;
        int found, err = 0;
  +     WARN_CONSOLE_UNLOCKED();
+
        if (oldidx = newidx)
                return 0;
  @@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
  {
        int i, new_idx = -1, ret = 0;
  +     WARN_CONSOLE_UNLOCKED();
+
        if (!fbcon_has_console_bind)
                return 0;
  @@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info
*info)
  {
        int i, idx;
  +     WARN_CONSOLE_UNLOCKED();
+
        idx = info->node;
        for (i = first_fb_vc; i <= last_fb_vc; i++) {
                if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info

*info)
  static void fbcon_remap_all(int idx)
  {
        int i;
+
+       WARN_CONSOLE_UNLOCKED();
+
        for (i = first_fb_vc; i <= last_fb_vc; i++)
                set_con2fb_map(i, idx, 0);
  @@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info
*info)
  {
        int ret = 0, i, idx;
  +     WARN_CONSOLE_UNLOCKED();
+
        idx = info->node;
        fbcon_select_primary(info);

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Hi,

On 11-07-18 17:28, Daniel Vetter wrote:

On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede [off-list ref] wrote:

quoted

Hi,

On 11-07-18 17:07, Thomas Zimmermann wrote:

quoted

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

quoted

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

Hmm, so this option is already broken (in a way) then, my first reaction
to your mail was that we should just remove that option. But that seemed
a bit harsh to me so I've been working on a fix for the last 10 minutes
or so.

But if it is already broken I'm tempted to just remove the option and
be done with it.  We really need less cruft in the fbdev/fbcon code not
more.

Please don't remove it, it makes debugging kms driver issues on
initial modeset (which is usually run from framebuffer_register, while
hodling the console_lock) impossible.

OK, so if we don't remove it, we should probably make it so that it
can be used without triggering any WARN_ONs, which would require changing
the existing WARN_CONSOLE_UNLOCKED() so that the calls from drivers/tty/vt/vt.c
also do not trigger it ?

I guess one can just ignore the oopses when debugging, but debugging surely
would be easier if there are just no oopses ?

Regards,

Hans

-Daniel

quoted

quoted

WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
...' construct [1]. I thought about turning this into a config option.

Ah I noticed the #if but I did not notice that it was a "#if 1".

If you want to fix lockless_register_fb it really should be replaced
with a runtime check, not a Kconfig option. This would require having
some lockless variable in the console code itself, which then gets
set by the fbdev code during init based on its lockless_register_fb
setting.

But as said I think we should seriously consider just removing
lockless_register_fb.

Regards,

Hans

quoted

Best regards
Thomas

[1]

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203

quoted

#define WARN_FB_CONSOLE_UNLOCKED()                      \
         do {                                            \
                 if (unlikely(!lockless_register_fb))    \
                         WARN_CONSOLE_UNLOCKED();        \
         } while (0)

And use that instead?

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
   drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
   1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c

b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx, int

user)
         struct fb_info *oldinfo = NULL;
         int found, err = 0;
   +     WARN_CONSOLE_UNLOCKED();
+
         if (oldidx = newidx)
                 return 0;
   @@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
   {
         int i, new_idx = -1, ret = 0;
   +     WARN_CONSOLE_UNLOCKED();
+
         if (!fbcon_has_console_bind)
                 return 0;
   @@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct fb_info
*info)
   {
         int i, idx;
   +     WARN_CONSOLE_UNLOCKED();
+
         idx = info->node;
         for (i = first_fb_vc; i <= last_fb_vc; i++) {
                 if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info

*info)
   static void fbcon_remap_all(int idx)
   {
         int i;
+
+       WARN_CONSOLE_UNLOCKED();
+
         for (i = first_fb_vc; i <= last_fb_vc; i++)
                 set_con2fb_map(i, idx, 0);
   @@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct fb_info
*info)
   {
         int ret = 0, i, idx;
   +     WARN_CONSOLE_UNLOCKED();
+
         idx = info->node;
         fbcon_select_primary(info);

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

On Wed, 11 Jul 2018 17:35:10 +0200
Hans de Goede [off-list ref] wrote:

OK, so if we don't remove it, we should probably make it so that it
can be used without triggering any WARN_ONs, which would require changing
the existing WARN_CONSOLE_UNLOCKED() so that the calls from drivers/tty/vt/vt.c
also do not trigger it ?

I guess one can just ignore the oopses when debugging, but debugging surely
would be easier if there are just no oopses ?

What about adding this patch (untested, not even compiled), and then
set it from the fb module.

-- Steve

diff --git a/include/linux/console.h b/include/linux/console.h
index dfd6b0e97855..11cd4956a57f 100644
--- a/include/linux/console.h
+++ b/include/linux/console.h

@@ -200,8 +200,10 @@ void vcs_make_sysfs(int index);
 void vcs_remove_sysfs(int index);
 
 /* Some debug stub to catch some of the obvious races in the VT code */
+extern bool ignore_console_lock_warning;
 #if 1
-#define WARN_CONSOLE_UNLOCKED()	WARN_ON(!is_console_locked() && !oops_in_progress)
+#define WARN_CONSOLE_UNLOCKED()						\
+	WARN_ON(!ignore_console_lock_warning && !is_console_locked() && !oops_in_progress)
 #else
 #define WARN_CONSOLE_UNLOCKED()
 #endif

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 247808333ba4..fa15d7ddf0c4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c

@@ -66,6 +66,9 @@ int console_printk[4] = {
 	CONSOLE_LOGLEVEL_DEFAULT,	/* default_console_loglevel */
 };
 
+bool ignore_console_lock_warning;
+EXPORT_SYMBOL(ignore_console_lock_warning);
+
 /*
  * Low level drivers may need that to know if they can schedule in
  * their unblank() callback or not. So let's export it.

On Wed, Jul 11, 2018 at 5:35 PM, Hans de Goede [off-list ref] wrote:

Hi,

On 11-07-18 17:28, Daniel Vetter wrote:

quoted

On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede [off-list ref]
wrote:

quoted

Hi,

On 11-07-18 17:07, Thomas Zimmermann wrote:

quoted

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

quoted

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

Hmm, so this option is already broken (in a way) then, my first reaction
to your mail was that we should just remove that option. But that seemed
a bit harsh to me so I've been working on a fix for the last 10 minutes
or so.

But if it is already broken I'm tempted to just remove the option and
be done with it.  We really need less cruft in the fbdev/fbcon code not
more.

Please don't remove it, it makes debugging kms driver issues on
initial modeset (which is usually run from framebuffer_register, while
hodling the console_lock) impossible.

OK, so if we don't remove it, we should probably make it so that it
can be used without triggering any WARN_ONs, which would require changing
the existing WARN_CONSOLE_UNLOCKED() so that the calls from
drivers/tty/vt/vt.c
also do not trigger it ?

I guess one can just ignore the oopses when debugging, but debugging surely
would be easier if there are just no oopses ?

I'd say let's only bother with the ones in fbcon.c. Avoids the trouble
with having to expose the fb module option to vt.c somehow. The ones
in vt.c are as old as the git history (from a quick check at least),
and in my debugging they never have been annoying (or I somehow didn't
ever hit them, not idea).

Also note that none if this matters long-term because I have a really
fancy plan to fix up this entire console_locking mess, which will also
remove the need for the lockless_fb_register debug hack.
-Daniel

Regards,

Hans

quoted

-Daniel

quoted

quoted

WARN_CONSOLE_UNLOCKED is already protected by an '#ifdef 1 ... #else
...' construct [1]. I thought about turning this into a config option.

Ah I noticed the #if but I did not notice that it was a "#if 1".

If you want to fix lockless_register_fb it really should be replaced
with a runtime check, not a Kconfig option. This would require having
some lockless variable in the console code itself, which then gets
set by the fbdev code during init based on its lockless_register_fb
setting.

But as said I think we should seriously consider just removing
lockless_register_fb.

Regards,

Hans

quoted

Best regards
Thomas

[1]


https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/console.h#n203

quoted

#define WARN_FB_CONSOLE_UNLOCKED()                      \
         do {                                            \
                 if (unlikely(!lockless_register_fb))    \
                         WARN_CONSOLE_UNLOCKED();        \
         } while (0)

And use that instead?

-- Steve

quoted

Best regards
Thomas

quoted

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Daniel Vetter <redacted>
Reviewed-by: Sergey Senozhatsky <redacted>
Signed-off-by: Hans de Goede <redacted>
---
Changes in v3:
-New patch in v3 of this patchset

Changes in v4:
-Keep the comments about which fbcon functions need locks in place
---
   drivers/video/fbdev/core/fbcon.c | 11 +++++++++++
   1 file changed, 11 insertions(+)

diff --git a/drivers/video/fbdev/core/fbcon.c

b/drivers/video/fbdev/core/fbcon.c
index c910e74d46ff..cd8d52a967aa 100644

--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c

@@ -828,6 +828,8 @@ static int set_con2fb_map(int unit, int newidx,

int
user)
         struct fb_info *oldinfo = NULL;
         int found, err = 0;
   +     WARN_CONSOLE_UNLOCKED();
+
         if (oldidx = newidx)
                 return 0;
   @@ -3044,6 +3046,8 @@ static int fbcon_fb_unbind(int idx)
   {
         int i, new_idx = -1, ret = 0;
   +     WARN_CONSOLE_UNLOCKED();
+
         if (!fbcon_has_console_bind)
                 return 0;
   @@ -3094,6 +3098,8 @@ static int fbcon_fb_unregistered(struct
fb_info
*info)
   {
         int i, idx;
   +     WARN_CONSOLE_UNLOCKED();
+
         idx = info->node;
         for (i = first_fb_vc; i <= last_fb_vc; i++) {
                 if (con2fb_map[i] = idx)

@@ -3131,6 +3137,9 @@ static int fbcon_fb_unregistered(struct fb_info

*info)
   static void fbcon_remap_all(int idx)
   {
         int i;
+
+       WARN_CONSOLE_UNLOCKED();
+
         for (i = first_fb_vc; i <= last_fb_vc; i++)
                 set_con2fb_map(i, idx, 0);
   @@ -3177,6 +3186,8 @@ static int fbcon_fb_registered(struct
fb_info
*info)
   {
         int ret = 0, i, idx;
   +     WARN_CONSOLE_UNLOCKED();
+
         idx = info->node;
         fbcon_select_primary(info);

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

Hi,

On 11-07-18 17:42, Daniel Vetter wrote:

On Wed, Jul 11, 2018 at 5:35 PM, Hans de Goede [off-list ref] wrote:

quoted

Hi,

On 11-07-18 17:28, Daniel Vetter wrote:

quoted

On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede [off-list ref]
wrote:

quoted

Hi,

On 11-07-18 17:07, Thomas Zimmermann wrote:

quoted

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

quoted

What if you make lockless_register_fb visible to fbcon, and then we can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

Hmm, so this option is already broken (in a way) then, my first reaction
to your mail was that we should just remove that option. But that seemed
a bit harsh to me so I've been working on a fix for the last 10 minutes
or so.

But if it is already broken I'm tempted to just remove the option and
be done with it.  We really need less cruft in the fbdev/fbcon code not
more.

Please don't remove it, it makes debugging kms driver issues on
initial modeset (which is usually run from framebuffer_register, while
hodling the console_lock) impossible.

OK, so if we don't remove it, we should probably make it so that it
can be used without triggering any WARN_ONs, which would require changing
the existing WARN_CONSOLE_UNLOCKED() so that the calls from
drivers/tty/vt/vt.c
also do not trigger it ?

I guess one can just ignore the oopses when debugging, but debugging surely
would be easier if there are just no oopses ?

I'd say let's only bother with the ones in fbcon.c. Avoids the trouble
with having to expose the fb module option to vt.c somehow.

The plan was actually do the things the other way around, add a flag to
vt.c which when set disables the WARN_ON calls and then have fbdev[.ko]
set that when the fb.lockless_fb_register option is set.

The ones
in vt.c are as old as the git history (from a quick check at least),
and in my debugging they never have been annoying (or I somehow didn't
ever hit them, not idea).

There is a #if 1 #define #else #define empty around the WARN_CONSOLE_UNLOCKED()
call in include/linux/console.h I've the feeling that is there as a hack
to be able to quickly disable the WARN_ONs when debugging.

Have you seen Steven's suggestion which he send about the same time
as your mail I'm replying to here ? I personally think that doing
something like that makes sense (for as long as we have the need
for the lockless_fb_register debug hack).

Note I've 2 patches ready to go to only fix this in fbcon.c, but I
think a more thorough fix makes sense.

Regards,

Hans

On Wed, Jul 11, 2018 at 7:35 PM, Hans de Goede [off-list ref] wrote:

Hi,


On 11-07-18 17:42, Daniel Vetter wrote:

quoted

On Wed, Jul 11, 2018 at 5:35 PM, Hans de Goede [off-list ref]
wrote:

quoted

Hi,

On 11-07-18 17:28, Daniel Vetter wrote:

quoted

On Wed, Jul 11, 2018 at 5:14 PM, Hans de Goede [off-list ref]
wrote:

quoted

Hi,

On 11-07-18 17:07, Thomas Zimmermann wrote:

quoted

Hi

Am 11.07.2018 um 16:52 schrieb Steven Rostedt:

quoted

What if you make lockless_register_fb visible to fbcon, and then we
can
have a macro:

There are more of these macro invocations under drivers/tty/vt, which
also mess up the log during debugging.

Hmm, so this option is already broken (in a way) then, my first
reaction
to your mail was that we should just remove that option. But that
seemed
a bit harsh to me so I've been working on a fix for the last 10 minutes
or so.

But if it is already broken I'm tempted to just remove the option and
be done with it.  We really need less cruft in the fbdev/fbcon code not
more.

Please don't remove it, it makes debugging kms driver issues on
initial modeset (which is usually run from framebuffer_register, while
hodling the console_lock) impossible.

OK, so if we don't remove it, we should probably make it so that it
can be used without triggering any WARN_ONs, which would require changing
the existing WARN_CONSOLE_UNLOCKED() so that the calls from
drivers/tty/vt/vt.c
also do not trigger it ?

I guess one can just ignore the oopses when debugging, but debugging
surely
would be easier if there are just no oopses ?

I'd say let's only bother with the ones in fbcon.c. Avoids the trouble
with having to expose the fb module option to vt.c somehow.

The plan was actually do the things the other way around, add a flag to
vt.c which when set disables the WARN_ON calls and then have fbdev[.ko]
set that when the fb.lockless_fb_register option is set.

quoted

The ones
in vt.c are as old as the git history (from a quick check at least),
and in my debugging they never have been annoying (or I somehow didn't
ever hit them, not idea).

There is a #if 1 #define #else #define empty around the
WARN_CONSOLE_UNLOCKED()
call in include/linux/console.h I've the feeling that is there as a hack
to be able to quickly disable the WARN_ONs when debugging.

Have you seen Steven's suggestion which he send about the same time
as your mail I'm replying to here ? I personally think that doing
something like that makes sense (for as long as we have the need
for the lockless_fb_register debug hack).

Note I've 2 patches ready to go to only fix this in fbcon.c, but I
think a more thorough fix makes sense.

Yeah Steven's suggestion looks reasonable to fix this all for good.
The #if 1 predates git history, so no idea why it was added or by whom
:-)
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

On Wed, 11 Jul 2018 19:56:02 +0200
Daniel Vetter [off-list ref] wrote:

quoted

Have you seen Steven's suggestion which he send about the same time
as your mail I'm replying to here ? I personally think that doing
something like that makes sense (for as long as we have the need
for the lockless_fb_register debug hack).

Note I've 2 patches ready to go to only fix this in fbcon.c, but I
think a more thorough fix makes sense.  

Yeah Steven's suggestion looks reasonable to fix this all for good.
The #if 1 predates git history, so no idea why it was added or by whom
:-)

I just sent the patch. If the printk maintainers take it, then you can
update the fb driver to set the ignore_console_lock_warning when
lockless_fb_register is set.

-- Steve

Hi,

On 11-07-18 21:19, Steven Rostedt wrote:

On Wed, 11 Jul 2018 19:56:02 +0200
Daniel Vetter [off-list ref] wrote:

quoted

quoted

Have you seen Steven's suggestion which he send about the same time
as your mail I'm replying to here ? I personally think that doing
something like that makes sense (for as long as we have the need
for the lockless_fb_register debug hack).

Note I've 2 patches ready to go to only fix this in fbcon.c, but I
think a more thorough fix makes sense.

Yeah Steven's suggestion looks reasonable to fix this all for good.
The #if 1 predates git history, so no idea why it was added or by whom
:-)

I just sent the patch. If the printk maintainers take it, then you can
update the fb driver to set the ignore_console_lock_warning when
lockless_fb_register is set.

Thanks for doing this. I will wait with sending a fbcon / fbdev patch
till the fate of your patch is clear then.

Regards,

Hans

Hi,

On (07/11/18 16:46), Thomas Zimmermann wrote:

Am 28.06.2018 um 11:03 schrieb Hans de Goede:

quoted

Replace comments about places where the console lock should be held with
calls to WARN_CONSOLE_UNLOCKED() to assert that it is actually held.

Debugging fbcon sometimes requires to not take the console lock. This
patch breaks the debugging workaround provided by
'fb.lockless_register_fb'. The dmesg is now filled with warnings about
the missing lock.

Hmm. I once dealt with WARN_CONSOLE_UNLOCKED(), and back then, IIRC,
I really wanted to turn it into WARN_ONCE_CONSOLE_UNLOCKED(), which
would WARN_ON_ONCE() instead of WARN_ON(). It's just a bit too noisy
and verbose and a single backtrace was already enough.

	-ss

Am 11.07.2018 um 21:19 schrieb Steven Rostedt:

I just sent the patch. If the printk maintainers take it, then you can
update the fb driver to set the ignore_console_lock_warning when
lockless_fb_register is set.

Thank you.

-- Steve
_______________________________________________
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-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Linux GmbH, Maxfeldstr. 5, D-90409 Nürnberg
Tel: +49-911-74053-0; Fax: +49-911-7417755;  https://www.suse.com/
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard,
Graham Norton, HRB 21284 (AG Nürnberg)