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

[andriy.shevchenko@xxxxxxxxxxxxxxx]

On Sat, Feb 22, 2025 at 03:46:03PM +0000, Aditya Garg wrote:
> > On 20 Feb 2025, at 10:09 PM, Aditya Garg <gargaditya08@xxxxxxxx> 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.

> [1]: https://lore.kernel.org/asahi/E753B391-D2CB-4213-AF82-678ADD5A7644@xxxxxxxxxxx/
> 
> 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