linux-kernel - Re: [PATCH] drm/stm: Avoid using val uninitialized in ltdc_set_ycbcr

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Date:   Tue, 22 Feb 2022 11:54:04 +0100
From:   Philippe CORNU <philippe.cornu@...s.st.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <nathan@...nel.org>
CC:     Yannick Fertre <yannick.fertre@...s.st.com>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        <dri-devel@...ts.freedesktop.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <llvm@...ts.linux.dev>
Subject: Re: [PATCH] drm/stm: Avoid using val uninitialized in
 ltdc_set_ycbcr_config()



On 2/7/22 8:44 PM, Nick Desaulniers wrote:
> On Mon, Feb 7, 2022 at 8:53 AM Nathan Chancellor <nathan@...nel.org> wrote:
>>
>> Clang warns:
>>
>>    drivers/gpu/drm/stm/ltdc.c:625:2: warning: variable 'val' is used uninitialized whenever switch default is taken [-Wsometimes-uninitialized]
>>            default:
>>            ^~~~~~~
>>    drivers/gpu/drm/stm/ltdc.c:635:2: note: uninitialized use occurs here
>>            val |= LxPCR_YCEN;
>>            ^~~
>>    drivers/gpu/drm/stm/ltdc.c:600:9: note: initialize the variable 'val' to silence this warning
>>            u32 val;
>>                   ^
>>                    = 0
>>    1 warning generated.
>>
>> Use a return instead of break in the default case to fix the warning.
>> Add an error message so that this return is not silent, which could hide
>> issues in the future.
>>
>> Fixes: 484e72d3146b ("drm/stm: ltdc: add support of ycbcr pixel formats")
>> Link: https://github.com/ClangBuiltLinux/linux/issues/1575
>> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
>> ---
>>   drivers/gpu/drm/stm/ltdc.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/stm/ltdc.c b/drivers/gpu/drm/stm/ltdc.c
>> index 5eeb32c9c9ce..447ddde1786c 100644
>> --- a/drivers/gpu/drm/stm/ltdc.c
>> +++ b/drivers/gpu/drm/stm/ltdc.c
>> @@ -624,7 +624,8 @@ static inline void ltdc_set_ycbcr_config(struct drm_plane *plane, u32 drm_pix_fm
>>                  break;
>>          default:
>>                  /* RGB or not a YCbCr supported format */
>> -               break;
>> +               drm_err(plane->dev, "Unsupported pixel format: %u\n", drm_pix_fmt);
> 
> This is fine, but in the future you should add an explicit
> #include <drm/drm_print.h>
> to avoid implicit header dependencies (like the ones that Mingo is
> trying to detangle) for the declaration of drm_err. `drm_vprintf`
> needs it, too.
> 
> Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
> 

Hi Nick,
and thank you for having pointing this.

Hi Nathan,
May I ask you please to update your patch changing drm_err(plane->dev, ) 
with DRM_ERROR().


Big thank you,

Philippe :-)



>> +               return;
>>          }
>>
>>          /* Enable limited range */
>>
>> base-commit: 542898c5aa5c6a3179dffb1d1606884a63f75fed
>> --
>> 2.35.1
>>
> 
>