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

[yannick Fertre]

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@xxxxxxxxxxx>
>
> <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?

Best regards