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

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Date:   Tue, 22 Feb 2022 08:23:27 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Philippe CORNU <philippe.cornu@...s.st.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        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 Tue, Feb 22, 2022 at 11:54:04AM +0100, Philippe CORNU wrote:
> 
> 
> 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().

Sure thing, v2 has been sent:

https://lore.kernel.org/r/20220222152045.484610-1-nathan@kernel.org/

I used drm_err() as I saw DRM_ERROR() was deprecated but I get internal
driver consistency is important.

Cheers,
Nathan

> Big thank you,
> 
> Philippe :-)
> 
> 
> 
> > > +               return;
> > >          }
> > > 
> > >          /* Enable limited range */
> > > 
> > > base-commit: 542898c5aa5c6a3179dffb1d1606884a63f75fed
> > > --
> > > 2.35.1
> > > 
> > 
> >