linux-kernel - Re: [PATCH 5/5] drm/stm: ltdc: add support of ycbcr pixel formats

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Date:   Mon, 7 Feb 2022 09:54:26 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     yannick Fertre <yannick.fertre@...s.st.com>
Cc:     Philippe Cornu <philippe.cornu@...s.st.com>,
        Raphael Gallais-Pou <raphael.gallais-pou@...s.st.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        dri-devel@...ts.freedesktop.org,
        linux-stm32@...md-mailman.stormreply.com,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] drm/stm: ltdc: add support of ycbcr pixel formats

On Mon, Feb 07, 2022 at 11:00:34AM +0100, yannick Fertre wrote:
> Hi Nathan,
> 
> On 2/2/22 17:54, Nathan Chancellor wrote:
> > Hi Yannick,
> > 
> > On Wed, Dec 15, 2021 at 10:48:43PM +0100, Yannick Fertre wrote:
> > > This patch adds the following YCbCr input pixel formats on the latest
> > > LTDC hardware version:
> > > 
> > > 1 plane  (co-planar)  : YUYV, YVYU, UYVY, VYUY
> > > 2 planes (semi-planar): NV12, NV21
> > > 3 planes (full-planar): YU12=I420=DRM YUV420, YV12=DRM YVU420
> > > 
> > > Signed-off-by: Yannick Fertre <yannick.fertre@...s.st.com>
> > 
> > <snip>
> > 
> > > +static inline void ltdc_set_ycbcr_config(struct drm_plane *plane, u32 drm_pix_fmt)
> > > +{
> > > +	struct ltdc_device *ldev = plane_to_ltdc(plane);
> > > +	struct drm_plane_state *state = plane->state;
> > > +	u32 lofs = plane->index * LAY_OFS;
> > > +	u32 val;
> > > +
> > > +	switch (drm_pix_fmt) {
> > > +	case DRM_FORMAT_YUYV:
> > > +		val = (YCM_I << 4) | LxPCR_YF | LxPCR_CBF;
> > > +		break;
> > > +	case DRM_FORMAT_YVYU:
> > > +		val = (YCM_I << 4) | LxPCR_YF;
> > > +		break;
> > > +	case DRM_FORMAT_UYVY:
> > > +		val = (YCM_I << 4) | LxPCR_CBF;
> > > +		break;
> > > +	case DRM_FORMAT_VYUY:
> > > +		val = (YCM_I << 4);
> > > +		break;
> > > +	case DRM_FORMAT_NV12:
> > > +		val = (YCM_SP << 4) | LxPCR_CBF;
> > > +		break;
> > > +	case DRM_FORMAT_NV21:
> > > +		val = (YCM_SP << 4);
> > > +		break;
> > > +	case DRM_FORMAT_YUV420:
> > > +	case DRM_FORMAT_YVU420:
> > > +		val = (YCM_FP << 4);
> > > +		break;
> > > +	default:
> > > +		/* RGB or not a YCbCr supported format */
> > > +		break;
> > > +	}
> > > +
> > > +	/* Enable limited range */
> > > +	if (state->color_range == DRM_COLOR_YCBCR_LIMITED_RANGE)
> > > +		val |= LxPCR_YREN;
> > > +
> > > +	/* enable ycbcr conversion */
> > > +	val |= LxPCR_YCEN;
> > > +
> > > +	regmap_write(ldev->regmap, LTDC_L1PCR + lofs, val);
> > > +}
> > 
> > This patch as commit 484e72d3146b ("drm/stm: ltdc: add support of ycbcr
> > pixel formats") in -next introduced the following clang warning:
> > 
> > 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.
> > 
> > Would it be okay to just return in the default case (maybe with a
> > message about an unsupported format?) or should there be another fix?
> > 
> > Cheers,
> 
> 
> Thanks for your help.
> It'okay for a message for unsupported format with a return in the default
> case.
> Do you want create & push the patch?

Thank you for the input! I have sent a fix now, please take a look.

https://lore.kernel.org/r/20220207165304.1046867-1-nathan@kernel.org/

Cheers,
Nathan