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Message-ID: <b74df4b5-ecda-45ba-a98a-c84b0a29e380@suse.de>
Date: Wed, 12 Mar 2025 12:46:16 +0100
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Aditya Garg <gargaditya08@...e.com>, Aun-Ali Zaidi <admin@...eit.net>,
Maxime Ripard <mripard@...nel.org>, "airlied@...hat.com"
<airlied@...hat.com>, Simona Vetter <simona@...ll.ch>,
"andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
"senozhatsky@...omium.org" <senozhatsky@...omium.org>,
Jonathan Corbet <corbet@....net>, Andrew Morton <akpm@...ux-foundation.org>,
"apw@...onical.com" <apw@...onical.com>, "joe@...ches.com"
<joe@...ches.com>, "dwaipayanray1@...il.com" <dwaipayanray1@...il.com>,
"lukas.bulwahn@...il.com" <lukas.bulwahn@...il.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
Hector Martin <marcan@...can.st>, Sven Peter <sven@...npeter.dev>,
Asahi Linux Mailing List <asahi@...ts.linux.dev>
Subject: Re: [PATCH 1/2] lib/vsprintf: Add support for generic FourCCs by
extending %p4cc
Hi
Am 12.03.25 um 10:05 schrieb Aditya Garg:
> From: Hector Martin <marcan@...can.st>
>
> %p4cc is designed for DRM/V4L2 FourCCs with their specific quirks, but
> it's useful to be able to print generic 4-character codes formatted as
> an integer. Extend it to add format specifiers for printing generic
> 32-bit FourCCs with various endian semantics:
>
> %p4ch Host byte order
> %p4cn Network byte order
> %p4cl Little-endian
> %p4cb Big-endian
That looks like someone trying to be too clever for their own good. Just
my 2 cts.
Best regards
Thomas
>
> The endianness determines how bytes are interpreted as a u32, and the
> FourCC is then always printed MSByte-first (this is the opposite of
> V4L/DRM FourCCs). This covers most practical cases, e.g. %p4cn would
> allow printing LSByte-first FourCCs stored in host endian order
> (other than the hex form being in character order, not the integer
> value).
>
> Acked-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Signed-off-by: Hector Martin <marcan@...can.st>
> Signed-off-by: Aditya Garg <gargaditya08@...e.com>
> ---
> Documentation/core-api/printk-formats.rst | 32 +++++++++++++++++++
> lib/test_printf.c | 39 +++++++++++++++++++----
> lib/vsprintf.c | 35 ++++++++++++++++----
> scripts/checkpatch.pl | 2 +-
> 4 files changed, 94 insertions(+), 14 deletions(-)
>
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index ecccc0473..bd420e8aa 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -648,6 +648,38 @@ Examples::
> %p4cc Y10 little-endian (0x20303159)
> %p4cc NV12 big-endian (0xb231564e)
>
> +Generic FourCC code
> +-------------------
> +
> +::
> + %p4c[hnlb] gP00 (0x67503030)
> +
> +Print a generic FourCC code, as both ASCII characters and its numerical
> +value as hexadecimal.
> +
> +The generic FourCC code is always printed in the big-endian format,
> +the most significant byte first. This is the opposite of V4L/DRM FourCCs.
> +
> +The additional ``h``, ``n``, ``l``, and ``b`` specifiers define what
> +endianness is used to load the stored bytes. The data might be interpreted
> +using the host byte order, network byte order, little-endian, or big-endian.
> +
> +Passed by reference.
> +
> +Examples for a little-endian machine, given &(u32)0x67503030::
> +
> + %p4ch gP00 (0x67503030)
> + %p4cn 00Pg (0x30305067)
> + %p4cl gP00 (0x67503030)
> + %p4cb 00Pg (0x30305067)
> +
> +Examples for a big-endian machine, given &(u32)0x67503030::
> +
> + %p4ch gP00 (0x67503030)
> + %p4cn 00Pg (0x30305067)
> + %p4cl 00Pg (0x30305067)
> + %p4cb gP00 (0x67503030)
> +
> Rust
> ----
>
> diff --git a/lib/test_printf.c b/lib/test_printf.c
> index 59dbe4f9a..b9e8afc01 100644
> --- a/lib/test_printf.c
> +++ b/lib/test_printf.c
> @@ -776,21 +776,46 @@ static void __init fwnode_pointer(void)
> software_node_unregister_node_group(group);
> }
>
> +struct fourcc_struct {
> + u32 code;
> + const char *str;
> +};
> +
> +static void __init fourcc_pointer_test(const struct fourcc_struct *fc, size_t n,
> + const char *fmt)
> +{
> + size_t i;
> +
> + for (i = 0; i < n; i++)
> + test(fc[i].str, fmt, &fc[i].code);
> +}
> +
> static void __init fourcc_pointer(void)
> {
> - struct {
> - u32 code;
> - char *str;
> - } const try[] = {
> + static const struct fourcc_struct try_cc[] = {
> { 0x3231564e, "NV12 little-endian (0x3231564e)", },
> { 0xb231564e, "NV12 big-endian (0xb231564e)", },
> { 0x10111213, ".... little-endian (0x10111213)", },
> { 0x20303159, "Y10 little-endian (0x20303159)", },
> };
> - unsigned int i;
> + static const struct fourcc_struct try_ch[] = {
> + { 0x41424344, "ABCD (0x41424344)", },
> + };
> + static const struct fourcc_struct try_cn[] = {
> + { 0x41424344, "DCBA (0x44434241)", },
> + };
> + static const struct fourcc_struct try_cl[] = {
> + { (__force u32)cpu_to_le32(0x41424344), "ABCD (0x41424344)", },
> + };
> + static const struct fourcc_struct try_cb[] = {
> + { (__force u32)cpu_to_be32(0x41424344), "ABCD (0x41424344)", },
> + };
>
> - for (i = 0; i < ARRAY_SIZE(try); i++)
> - test(try[i].str, "%p4cc", &try[i].code);
> + fourcc_pointer_test(try_cc, ARRAY_SIZE(try_cc), "%p4cc");
> + fourcc_pointer_test(try_ch, ARRAY_SIZE(try_ch), "%p4ch");
> + fourcc_pointer_test(try_cn, ARRAY_SIZE(try_cn), "%p4cn");
> + fourcc_pointer_test(try_cl, ARRAY_SIZE(try_cl), "%p4cl");
> + fourcc_pointer_test(try_cb, ARRAY_SIZE(try_cb), "%p4cb");
> }
>
> static void __init
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 56fe96319..56511a994 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1781,27 +1781,50 @@ char *fourcc_string(char *buf, char *end, const u32 *fourcc,
> char output[sizeof("0123 little-endian (0x01234567)")];
> char *p = output;
> unsigned int i;
> + bool pixel_fmt = false;
> u32 orig, val;
>
> - if (fmt[1] != 'c' || fmt[2] != 'c')
> + if (fmt[1] != 'c')
> return error_string(buf, end, "(%p4?)", spec);
>
> if (check_pointer(&buf, end, fourcc, spec))
> return buf;
>
> orig = get_unaligned(fourcc);
> - val = orig & ~BIT(31);
> + switch (fmt[2]) {
> + case 'h':
> + break;
> + case 'n':
> + orig = swab32(orig);
> + break;
> + case 'l':
> + orig = (__force u32)cpu_to_le32(orig);
> + break;
> + case 'b':
> + orig = (__force u32)cpu_to_be32(orig);
> + break;
> + case 'c':
> + /* Pixel formats are printed LSB-first */
> + pixel_fmt = true;
> + break;
> + default:
> + return error_string(buf, end, "(%p4?)", spec);
> + }
> +
> + val = pixel_fmt ? swab32(orig & ~BIT(31)) : orig;
>
> for (i = 0; i < sizeof(u32); i++) {
> - unsigned char c = val >> (i * 8);
> + unsigned char c = val >> ((3 - i) * 8);
>
> /* Print non-control ASCII characters as-is, dot otherwise */
> *p++ = isascii(c) && isprint(c) ? c : '.';
> }
>
> - *p++ = ' ';
> - strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
> - p += strlen(p);
> + if (pixel_fmt) {
> + *p++ = ' ';
> + strcpy(p, orig & BIT(31) ? "big-endian" : "little-endian");
> + p += strlen(p);
> + }
>
> *p++ = ' ';
> *p++ = '(';
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 7b28ad331..5595a0898 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6904,7 +6904,7 @@ sub process {
> ($extension eq "f" &&
> defined $qualifier && $qualifier !~ /^w/) ||
> ($extension eq "4" &&
> - defined $qualifier && $qualifier !~ /^cc/)) {
> + defined $qualifier && $qualifier !~ /^c[hnlbc]/)) {
> $bad_specifier = $specifier;
> last;
> }
--
--
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)
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