Hi Sam
Am 02.05.23 um 22:03 schrieb Sam Ravnborg:
Hi Thomas,
On Tue, May 02, 2023 at 03:02:22PM +0200, Thomas Zimmermann wrote:
quoted
Implement framebuffer I/O helpers, such as fb_read*() and fb_write*(),
in the architecture's <asm/fb.h> header file or the generic one.
In reality they are now all implemented in the generic one.
quoted
The common case has been the use of regular I/O functions, such as
__raw_readb() or memset_io(). A few architectures used plain system-
memory reads and writes. Sparc used helpers for its SBus.
The architectures that used special cases provide the same code in
their __raw_*() I/O helpers. So the patch replaces this code with the
__raw_*() functions and moves it to <asm-generic/fb.h> for all
architectures.
Which is also documented here.
The first paragraph documents the design intention, the other one the implementation. But I agree that it's not well phrased. I'll see if I can improve the text.
quoted
v3:
* implement all architectures with generic helpers
* support reordering and native byte order (Geert, Arnd)
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
include/asm-generic/fb.h | 101 +++++++++++++++++++++++++++++++++++++++
include/linux/fb.h | 53 --------------------
2 files changed, 101 insertions(+), 53 deletions(-)
diff --git a/include/asm-generic/fb.h b/include/asm-generic/fb.h
index 6922dd248c51..0540eccdbeca 100644
--- a/include/asm-generic/fb.h
+++ b/include/asm-generic/fb.h
@@ -31,4 +31,105 @@ static inline int fb_is_primary_device(struct fb_info *info)
}
#endif
+/*
+ * I/O helpers for the framebuffer. Prefer these functions over their
+ * regular counterparts. The regular I/O functions provide in-order
+ * access and swap bytes to/from little-endian ordering. Neither is
+ * required for framebuffers. Instead, the helpers read and write
+ * raw framebuffer data. Independent operations can be reordered for
+ * improved performance.
+ */
+
+#ifndef fb_readb
+static inline u8 fb_readb(const volatile void __iomem *addr)
+{
+ return __raw_readb(addr);
+}
+#define fb_readb fb_readb
+#endif
When we need to provide an architecture specific variant the
#ifndef foo
...
#define foo foo
can be added. Right now it is just noise as no architectures provide
their own variants.
Given Arnd's comments, this might change. It also makes sense from a design POV.
But I am missing something somewhere as I cannot see how this builds.
asm-generic now provide the fb_read/fb_write helpers.
But for example sparc has an architecture specifc fb.h so it will not
use the asm-generic variant. So I wonder how sparc get hold of the
asm-generic fb.h file?
All architecture's <asm/fb.h> files include <asm-generic/fb.h>, so that they all get the interfaces which they don't define themselves. For Sparc, this is at [1].
Best regards
Thomas
[1] https://cgit.freedesktop.org/drm/drm-tip/tree/arch/sparc/include/asm/fb.h#n19
Maybe it is obvious, but I miss it.
Sam
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)