Re: [PATCH v9 1/5] drm/mediatek: ovl: Fix XRGB format breakage for blend_modes unsupported SoCs

[AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>]

Il 07/10/24 09:00, Jason-JH.Lin ha scritto:
> If the constant alpha always enable, the SoCs that is not supported the
> ignore pixel alpha bit will still use constant alpha. That will break
> the original constant alpha setting of XRGB foramt for blend_modes
> unsupported SoCs, such as MT8173.
> 
> Note that ignore pixel alpha bit is suppored if the SoC support the
> blend_modes.
> Make the constatnt alpha only enable when having a vliad blend_mode or
> setting the has_alpha to fix the downgrade issue.
> 
> Fixes: bc46eb5d5d77 ("drm/mediatek: Support DRM plane alpha in OVL")
> Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
> ---
>   drivers/gpu/drm/mediatek/mtk_disp_ovl.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> index 89b439dcf3a6..8453a72f9e59 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_ovl.c
> @@ -473,8 +473,14 @@ void mtk_ovl_layer_config(struct device *dev, unsigned int idx,
>   
>   	con = ovl_fmt_convert(ovl, fmt, blend_mode);
>   	if (state->base.fb) {
> -		con |= OVL_CON_AEN;
>   		con |= state->base.alpha & OVL_CON_ALPHA;
> +
> +		/*
> +		 * For blend_modes supported SoCs, always enable constant alpha.
> +		 * For blend_modes unsupported SoCs, enable constant alpha when has_alpha is set.
> +		 */
> +		if (blend_mode || state->base.fb->format->has_alpha)
> +			con |= OVL_CON_AEN;

I'd say that you should make sure that OVL_CON_AEN is not set when
!blend_mode && !has_alpha, and you can do that like this:

		if (blend_mode || state->base.fb->format->has_alpha)
			con |= OVL_CON_AEN;
		else
			con &= ~OVL_CON_AEN;

After applying the proposed change,
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>