OVL_CON_AEN is for alpha blending enable.
For the SoC that is supported the blend_modes, OVL_CON_AEN will always
enabled to use constant alpha and then use the ignore_pixel_alpha bit
to do the alpha blending for XRGB8888 format.
Note that ignore pixel alpha bit is not supported if the SoC is not
supported the blend_modes.
So it will break the original setting of XRGB8888 foramt for the
blend_modes unsupported SoCs, such as MT8173.

To fix the downgrade issue, enable alpha blending only when a valid
blend_mode or has_alpha is set.

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..047cd1796a51 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 alpha blending.
+		 * For blend_modes unsupported SoCs, enable alpha blending when has_alpha is set.
+		 */
+		if (blend_mode || state->base.fb->format->has_alpha)
+			con |= OVL_CON_AEN;
 	}
 
 	/* CONST_BLD must be enabled for XRGB formats although the alpha channel
-- 
2.43.0

Hi, Jason:

On Tue, 2024-10-08 at 14:47 +0800, Jason-JH.Lin wrote:
> OVL_CON_AEN is for alpha blending enable.
> For the SoC that is supported the blend_modes, OVL_CON_AEN will always
> enabled to use constant alpha and then use the ignore_pixel_alpha bit
> to do the alpha blending for XRGB8888 format.
> Note that ignore pixel alpha bit is not supported if the SoC is not
> supported the blend_modes.
> So it will break the original setting of XRGB8888 foramt for the
> blend_modes unsupported SoCs, such as MT8173.
> 
> To fix the downgrade issue, enable alpha blending only when a valid
> blend_mode or has_alpha is set.

After fixing the typo mentioned by Markus,

Reviewed-by: CK Hu <ck.hu@mediatek.com>

> 
> 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..047cd1796a51 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 alpha blending.
> +		 * For blend_modes unsupported SoCs, enable alpha blending when has_alpha is set.
> +		 */
> +		if (blend_mode || state->base.fb->format->has_alpha)
> +			con |= OVL_CON_AEN;
>  	}
>  
>  	/* CONST_BLD must be enabled for XRGB formats although the alpha channel

…
> Note that ignore pixel alpha bit is not supported if the SoC is not
> supported the blend_modes.

  supporting the blending modes?


> So it will break the original setting of XRGB8888 foramt for the

                                                    format?


> Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>

Would a personal name without a dot be preferred
according to the Developer's Certificate of Origin?
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.12-rc2#n396

Regards,
Markus

On Tue, 2024-10-08 at 09:55 +0200, Markus Elfring wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  …
> > Note that ignore pixel alpha bit is not supported if the SoC is not
> > supported the blend_modes.
> 
>   supporting the blending modes?
> 
> 
> > So it will break the original setting of XRGB8888 foramt for the
> 
>                                                     format?

Thanks! I'll fix this typo at the next version.

Regards,
Jason-JH.Lin

> 
> 
> > Signed-off-by: Jason-JH.Lin <jason-jh.lin@mediatek.com>
> 
> Would a personal name without a dot be preferred
> according to the Developer's Certificate of Origin?
> 
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst?h=v6.12-rc2#n396
> 
> Regards,
> Markus