linux-kernel - Re: [PATCH v9 1/5] drm/mediatek: ovl: Fix XRGB format breakage for blend

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Message-ID: <703213a8-1ac6-4c8d-9487-ea1dbdabec40@collabora.com>
Date: Mon, 7 Oct 2024 11:36:35 +0200
From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
To: "Jason-JH.Lin" <jason-jh.lin@...iatek.com>,
 Adam Thiede <me@...mthiede.com>, Yassine Oudjana
 <yassine.oudjana@...il.com>, Chun-Kuang Hu <chunkuang.hu@...nel.org>
Cc: Shawn Sung <shawn.sung@...iatek.com>,
 Alper Nebi Yasak <alpernebiyasak@...il.com>,
 dri-devel@...ts.freedesktop.org, linux-mediatek@...ts.infradead.org,
 linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 Singo Chang <singo.chang@...iatek.com>, Nancy Lin <nancy.lin@...iatek.com>,
 Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v9 1/5] drm/mediatek: ovl: Fix XRGB format breakage for
 blend_modes unsupported SoCs

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@...iatek.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@...labora.com>