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

["Jason-JH Lin (林睿祥)" <Jason-JH.Lin@mediatek.com>]

Hi Angelo,

Thanks for the reviews.

On Mon, 2024-10-07 at 11:36 +0200, AngeloGioacchino Del Regno wrote:
> 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);

Because con is a local variable declared in the beginning of
mtk_ovl_layer_config() and then being assigned to the return value of
ovl_fmt_convert() here.

> >   	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;

I think the OVL_CON_AEN won't be set when !blend_mode && !has_alpha.
Can I drop the else case here?

> 		else
> 			con &= ~OVL_CON_AEN;

Regards,
Jason-JH.Lin

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