Re: [PATCH v7 1/3] lib/vsprintf: Add support for printing V4L2 and DRM fourccs

Hi Andy,

On Mon, Feb 15, 2021 at 03:31:29PM +0200, Andy Shevchenko wrote:

On Mon, Feb 15, 2021 at 01:40:28PM +0200, Sakari Ailus wrote:

quoted

Add a printk modifier %p4cc (for pixel format) for printing V4L2 and DRM
pixel formats denoted by fourccs. The fourcc encoding is the same for both
so the same implementation can be used.

This version I almost like, feel free to add
Reviewed-by: From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
after considering addressing below nit-picks.

quoted

Suggested-by: Mauro Carvalho Chehab <mchehab@kernel.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <redacted>
---
 Documentation/core-api/printk-formats.rst | 16 ++++++++++
 lib/test_printf.c                         | 17 ++++++++++
 lib/vsprintf.c                            | 39 +++++++++++++++++++++++
 scripts/checkpatch.pl                     |  6 ++--
 4 files changed, 76 insertions(+), 2 deletions(-)

diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
index 160e710d992f..da2aa065dc42 100644
--- a/Documentation/core-api/printk-formats.rst
+++ b/Documentation/core-api/printk-formats.rst

@@ -567,6 +567,22 @@ For printing netdev_features_t.
 
 Passed by reference.
 
+V4L2 and DRM FourCC code (pixel format)
+---------------------------------------
+
+::
+
+	%p4cc
+
+Print a FourCC code used by V4L2 or DRM, including format endianness and
+its numerical value as hexadecimal.
+
+Passed by reference.
+
+Examples::
+
+	%p4cc	BG12 little-endian (0x32314742)

No examples with spaces / non-printable / non-ascii characters

I can sure add an example that has a space. But do you think I really
should add an example where invalid information is being printed?

quoted

+
 Thanks
 ======
 

diff --git a/lib/test_printf.c b/lib/test_printf.c
index 7d60f24240a4..9848510a2786 100644
--- a/lib/test_printf.c
+++ b/lib/test_printf.c

@@ -647,6 +647,22 @@ static void __init fwnode_pointer(void)
 	software_node_unregister_nodes(softnodes);
 }
 
+static void __init fourcc_pointer(void)
+{
+	struct {
+		u32 code;
+		char *str;
+	} const try[] = {
+		{ 0x3231564e, "NV12 little-endian (0x3231564e)", },
+		{ 0xb231564e, "NV12 big-endian (0xb231564e)", },
+		{ 0x10111213, ".... little-endian (0x10111213)", },
+	};
+	unsigned int i;
+
+	for (i = 0; i < ARRAY_SIZE(try); i++)
+		test(try[i].str, "%p4cc", &try[i].code);
+}
+
 static void __init
 errptr(void)
 {

@@ -692,6 +708,7 @@ test_pointer(void)
 	flags();
 	errptr();
 	fwnode_pointer();
+	fourcc_pointer();
 }
 
 static void __init selftest(void)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3b53c73580c5..432b5a2d1e90 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c

@@ -1733,6 +1733,42 @@ char *netdev_bits(char *buf, char *end, const void *addr,
 	return special_hex_number(buf, end, num, size);
 }
 
+static noinline_for_stack
+char *fourcc_string(char *buf, char *end, const u32 *fourcc,
+		    struct printf_spec spec, const char *fmt)
+{
+	char output[sizeof("1234 little-endian (0x01234567)")];

1234 -> ABCD ? (Or XY12 to be closer to the reality)

I count in numbers... albeit the hexadecimal number there starts from zero.

I guess both would work though.

0123 would be consistent.

-- 
Regards,

Sakari Ailus