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

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Message-ID:
 <PN3PR01MB9597E5C609290DB1A967263CB8D02@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Wed, 12 Mar 2025 19:14:36 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: Sven Peter <sven@...npeter.dev>
CC: Thomas Zimmermann <tzimmermann@...e.de>, Aun-Ali Zaidi <admin@...eit.net>,
	Maxime Ripard <mripard@...nel.org>, "airlied@...hat.com"
	<airlied@...hat.com>, Simona Vetter <simona@...ll.ch>, Andy Shevchenko
	<andriy.shevchenko@...ux.intel.com>, Petr Mladek <pmladek@...e.com>, Steven
 Rostedt <rostedt@...dmis.org>, Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>, Jonathan Corbet
	<corbet@....net>, "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"apw@...onical.com" <apw@...onical.com>, "joe@...ches.com" <joe@...ches.com>,
	"dwaipayanray1@...il.com" <dwaipayanray1@...il.com>,
	"lukas.bulwahn@...il.com" <lukas.bulwahn@...il.com>, Linux Kernel Mailing
 List <linux-kernel@...r.kernel.org>, "dri-devel@...ts.freedesktop.org"
	<dri-devel@...ts.freedesktop.org>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, Hector Martin <marcan@...can.st>,
	"asahi@...ts.linux.dev" <asahi@...ts.linux.dev>
Subject: Re: [PATCH 1/2] lib/vsprintf: Add support for generic FourCCs by
 extending %p4cc



> On 12 Mar 2025, at 9:05 PM, Sven Peter <sven@...npeter.dev> wrote:
> 
> Hi,
> 
> 
> On Wed, Mar 12, 2025, at 13:03, Aditya Garg wrote:
>>>> On 12 Mar 2025, at 5:29 PM, Thomas Zimmermann <tzimmermann@...e.de> wrote:
>>> 
>>> Hi
>>> 
>>>> Am 12.03.25 um 12:49 schrieb Aditya Garg:
>>>> 
>>>>>> On 12 Mar 2025, at 5:16 PM, Thomas Zimmermann <tzimmermann@...e.de> wrote:
>>>>> 
>>>>> Hi
>>>>> 
>>>>>> Am 12.03.25 um 10:05 schrieb Aditya Garg:
>>>>>> From: Hector Martin <marcan@...can.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)

That seems to be a nice alternative, which I guess Thomas was also suggesting.

> 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