> On 12 Mar 2025, at 5:33 PM, Aditya Garg <gargadity...@live.com> wrote:
>
>
>
>> On 12 Mar 2025, at 5:29 PM, Thomas Zimmermann <tzimmerm...@suse.de> wrote:
>>
>> Hi
>>
>>>> Am 12.03.25 um 12:49 schrieb Aditya Garg:
>>>
>>>>> On 12 Mar 2025, at 5:16 PM, Thomas Zimmermann <tzimmerm...@suse.de> wrote:
>>>>
>>>> Hi
>>>>
>>>>> Am 12.03.25 um 10:05 schrieb Aditya Garg:
>>>>> From: Hector Martin <mar...@marcan.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.
>>> I don't understand what you are trying to say. Anyways, I thought it's
>>> obvious, but Petr's Ack is still left and thus cannot be merged into DRM
>>> for now unless he says so in this thread.
>>
>> I'm trying to say that the author of this patch found the %p4cc
>> functionality and over-generalized the feature. Source code should express
>> the idea of what it's doing in clear terms. %p4ch somehow doesn't do that
>> for me. Printing 4 bytes in various orders without context seems arbitrary
>> and confusing.
>>
>> (I don't really have a say here. I'm just asking to reconsider this change.)
>
> Ah I see. I'll checkout the macros you sent. The Asahi Linux SMC drivers
> would need these as well, so I'll probably first wait for the vsprintf
> maintainers and also Asahi Linux maintainers for their views.
>>
You also might have noticed that the FourCCs actually make sense in this
driver. Eg: REDY, CLRD stand for APPLETBDRM_MSG_SIGNAL_READINESS and
APPLETBDRM_MSG_CLEAR_DISPLAY respectively.
>> Best regards
>> Thomas
>>
>>>> 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 <li...@rasmusvillemoes.dk>
>>>>> Reviewed-by: Andy Shevchenko <andriy.shevche...@linux.intel.com>
>>>>> Signed-off-by: Hector Martin <mar...@marcan.st>
>>>>> Signed-off-by: Aditya Garg <gargadity...@live.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)
>>>>
>>
>> --
>> --
>> 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)
>>
