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

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Message-ID:
 <PN3PR01MB9597A8F02423B9E4C585F5EBB8D32@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Thu, 13 Mar 2025 09:13:23 +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 2:27 PM, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> 
> On Thu, Mar 13, 2025 at 08:53:28AM +0000, Aditya Garg wrote:
>>>> 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.
> 
> Right, it depends on the usage count. Also on different architectures it may
> give different results. On 32-bit it probably gives better statistics.

Best to go ahead with vsprintf then. Petr, are you still there?
> 
>>>>>>> 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
> 
>