Re: [PATCH] video: fbdev: matroxfb: remove dead code and set but not used variable

[Helge Deller <deller@gmx.de>]

On 3/19/26 10:08, Andy Shevchenko wrote:
> On Thu, Mar 19, 2026 at 09:35:33AM +0100, Helge Deller wrote:
>> On 3/19/26 09:21, Andy Shevchenko wrote:
>>> On Thu, Mar 19, 2026 at 04:06:44PM +0800, Jason Yan wrote:
>>>> 在 2026/3/19 15:38, Andy Shevchenko 写道:
>>>>> On Thu, Mar 19, 2026 at 10:22:08AM +0800, Jason Yan wrote:
> 
> ...
> 
>>>>> Helge, can we revert this change and start over, please? (I can also send
>>>>> revert if you think it's a better way)
>>
>> Andy, all points you make against removing relevant code is absolutely right.
>>
>> But for this specific commit 7b987887f97b ("video: fbdev: matroxfb: remove dead code and
>> set but not used variable") I have to agree with Jason, that the patch is ok.
>> I don't see any build errors either.
> 
> Just run on today's Linux Next (since the driver has not been changed in that
> sense for a few years, the very same issue is present for a long time):
> 
> drivers/video/fbdev/matrox/g450_pll.c:412:18: error: variable 'mnp' set but not used [-Werror,-Wunused-but-set-variable]
>    412 |                                 unsigned int mnp;
>        |                                              ^
> 1 error generated.

Ok.

  
>> Are we mixing up things here maybe?
> 
> ...
> 
> FWIW, I dove to the history of the driver.
> 
> So, the code, that was guarded by #if 0 was introduced in the original commit
> 213d22146d1f ("[PATCH] (1/3) matroxfb for 2.5.3"). And then guarded in the
> commit 705e41f82988 ("matroxfb DVI updates: Handle DVI output on G450/G550.
> Powerdown unused portions of G450/G550 DAC. Split G450/G550 DAC from older
> DAC1064 handling. Modify PLL setting when both CRTCs use same pixel clocks.").
> 
> Even without that guard the modern compilers may see that the pixel_vco wasn't
> ever used and seems a leftover after some debug or review made 25 years ago.
> 
> The g450_mnp2vco() doesn't have any IO and as Jason said doesn't seem to have
> any side effects either than some unneeded CPU processing during runtime. I
> agree that's unlikely that timeout (or heating up the CPU) has any effect on
> the HW (GPU/display) functionality.
> 
> So, since the commit 7b987887f97b ("video: fbdev: matroxfb: remove dead code
> and set but not used variable") the 'mnp' became unused, but eliminating that
> code might have side-effects. The question here is what should we do with mnp?
> The easiest way out is just mark it with __maybe_unused which will shut the
> compiler up and won't change any possible IO flow.

Yes, I think that's what I'd prefer.
Do you mind sending a patch?

Helge