[PATCH v2 2/3] lib/vsprintf: Add support for generic FOURCCs by extending %p4cc

[Aditya Garg]

> On 24 Feb 2025, at 3:28 PM, andriy.shevchenko at linux.intel.com wrote:
> 
> On Sat, Feb 22, 2025 at 03:46:03PM +0000, Aditya Garg wrote:
>>>> On 20 Feb 2025, at 10:09 PM, Aditya Garg <gargaditya08 at live.com> wrote:
>>> 
>>> %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-endian
>>> %p4cl Little-endian
>>> %p4cb Big-endian
>>> %p4cr Reverse-endian
>>> 
>>> 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. %p4cr would
>>> allow printing LSByte-first FOURCCs stored in host endian order
>>> (other than the hex form being in character order, not the integer
>>> value).
> 
> ...
> 
>> BTW, after looking at the comments by Martin [1], its actually better to use
>> existing specifiers for the appletbdrm driver.  The driver needs the host
>> endian as proposed by this patch, so instead of that, we can use %.4s
> 
> Do you mean this patch will not be needed? If this a case, that would be the
> best solution.

I tested with %4pE, and the results are different from expected. So this would be preferred. Kindly see my latest email with a proposed workaround for the sparse warnings.
> 
>> [1]: https://lore.kernel.org/asahi/E753B391-D2CB-4213-AF82-678ADD5A7644@cutebit.org/
>> 
>> Alternatively we could add a host endian only. Other endians are not really
>> used by any driver AFAIK. The host endian is being used by appletbdrm and
>> Asahi Linux’ SMC driver only.
> 
> --
> With Best Regards,
> Andy Shevchenko
> 
>