Re: [PATCH v5] lib/vsprintf: Add support for generic FourCCs by extending %p4cc

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Fri, Feb 28, 2025 at 04:29:12PM +0000, Aditya Garg wrote:
> From: Hector Martin <marcan@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-endian
> %p4cn	Reverse-endian

Call them Host order, Network order as they are very established endianesses.


> %p4cl   Little-endian

You have extra spaces here

> %p4cb	Big-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. %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).

...

> +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-endian, reverse-host-endian, little-endian, or big-endian.

host order, network order

> +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)


For the reference on the terms:
https://www.ibm.com/docs/ja/zvm/7.2?topic=domains-network-byte-order-host-byte-order

Otherwise LGTM. With the above addressed, FWIW,
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

-- 
With Best Regards,
Andy Shevchenko