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

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Date:   Mon, 7 Feb 2022 11:00:34 +0100
From:   yannick Fertre <yannick.fertre@...s.st.com>
To:     Nathan Chancellor <nathan@...nel.org>
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

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?

Best regards