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

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Message-ID:
 <PN3PR01MB959780176C0B16C36FBD59C3B8D32@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Thu, 13 Mar 2025 08:53:28 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC: Sven Peter <sven@...npeter.dev>, 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>,
	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 13 Mar 2025, at 2:19 PM, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> 
> On Thu, Mar 13, 2025 at 07:26:05AM +0000, Aditya Garg wrote:
>>>> On 13 Mar 2025, at 12:58 AM, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
>>> On Wed, Mar 12, 2025 at 07:14:36PM +0000, Aditya Garg wrote:
>>>>> On 12 Mar 2025, at 9:05 PM, Sven Peter <sven@...npeter.dev> wrote:
>>>>> On Wed, Mar 12, 2025, at 13:03, Aditya Garg wrote:
> 
> ...
> 
>>>>> 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.
>>> 
>>> I don't think it's "nice". Each of the approaches has pros and cons.
>>> You can start from bloat-o-meter here and compare it with your %p extension.
>>> 
>>> Also, can you show the bloat-o-meter output for the vsprintf.c?
>> 
>> Here are your outputs:
> 
> Thank you!
> 
>> ---------------------------------------------------------------------
>> For appletbdrm:
>> 
>> aditya@...Book:~/linux$ ./scripts/bloat-o-meter $P4 $MACRO
>> add/remove: 0/0 grow/shrink: 1/1 up/down: 64/-19 (45)
>> Function                                     old     new   delta
>> appletbdrm_read_response                     395     459     +64
>> appletbdrm_probe                            1786    1767     -19
>> Total: Before=13418, After=13463, chg +0.34%
> 
> This is enough, no need to repeat this for every parameter.
> 
>> ---------------------------------------------------------------------
>> For vsprintf:
>> 
>> aditya@...Book:~/linux$ ./scripts/bloat-o-meter $OLD $NEW
>> add/remove: 0/0 grow/shrink: 1/0 up/down: 220/0 (220)
>> Function                                     old     new   delta
>> fourcc_string                                479     699    +220
>> Total: Before=26454, After=26674, chg +0.83%
> 
> So, we get +220 bytes vs +43 bytes. It means if we found 5+ users, it worth
> doing.
> 

Will it also depend upon the number of times it's being used? In appletbdrm, it is being used 3 times. Probably more in Asahi SMC.
>>>>> 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));
> 
> --
> With Best Regards,
> Andy Shevchenko
> 
>