Re: [PATCH 1/2] lib/vsprintf: Add support for generic FourCCs by extending %p4cc

["Sven Peter" <sven@svenpeter.dev>]

Hi,


On Wed, Mar 12, 2025, at 13:03, Aditya Garg wrote:
>> On 12 Mar 2025, at 5:29 PM, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>> 
>> Hi
>> 
>>> Am 12.03.25 um 12:49 schrieb Aditya Garg:
>>> 
>>>>> On 12 Mar 2025, at 5:16 PM, Thomas Zimmermann <tzimmermann@suse.de> wrote:
>>>> 
>>>> Hi
>>>> 
>>>>> Am 12.03.25 um 10:05 schrieb Aditya Garg:
>>>>> 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 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.

I don't have a strong opinion either way: for SMC I just need to print
FourCC keys for debugging / information in a few places.

I'm preparing the SMC driver for upstreaming again (after a two year delay :-()
and was just going to use macros to print the SMC FourCC keys similar to
DRM_MODE_FMT/DRM_MODE_ARG for now to keep the series smaller and revisit
the topic later.

Right now I have these in my local tree (only compile tested so far):

#define SMC_KEY_FMT "%c%c%c%c (0x%08x)"
#define SMC_KEY_ARG(k) (k)>>24, (k)>>16, (k)>>8, (k), (k)

which are then used like this:

	dev_info(dev,
		"Initialized (%d keys " SMC_KEY_FMT " .. " SMC_KEY_FMT ")\n",
		 smc->key_count, SMC_KEY_ARG(smc->first_key),
		 SMC_KEY_ARG(smc->last_key));

Best,

Sven