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@xxxxxxxxxxxx>
---
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
