[PATCH v2] drm/sun4i: Enable output signal premultiplication for DE2/DE3

[Roman Stratiienko <r.stratiienko@gmail.com>]

Otherwise alpha value is discarded, resulting incorrect pixel
apperance on the display.

This also fixes missing transparency for the most bottom layer.

Test applications and videos w/ w/o this patch are available at [1].

[1]: https://github.com/GloDroid/glodroid_tests/issues/1
Signed-off-by: Roman Stratiienko <r.stratiienko@gmail.com>

---
Changelog:

V2: Added code hunk missing in v1
---
 drivers/gpu/drm/sun4i/sun8i_mixer.c | 5 +++--
 drivers/gpu/drm/sun4i/sun8i_mixer.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.c b/drivers/gpu/drm/sun4i/sun8i_mixer.c
index 6b1711a9a71f..ba2932aaed08 100644
--- a/drivers/gpu/drm/sun4i/sun8i_mixer.c
+++ b/drivers/gpu/drm/sun4i/sun8i_mixer.c
@@ -320,8 +320,9 @@ static void sun8i_mixer_mode_set(struct sunxi_engine *engine,
 	else
 		val = 0;
 
-	regmap_update_bits(engine->regs, SUN8I_MIXER_BLEND_OUTCTL(bld_base),
-			   SUN8I_MIXER_BLEND_OUTCTL_INTERLACED, val);
+	val |= SUN8I_MIXER_BLEND_OUTCTL_PREMULTIPLY;
+
+	regmap_write(engine->regs, SUN8I_MIXER_BLEND_OUTCTL(bld_base), val);
 
 	DRM_DEBUG_DRIVER("Switching display mixer interlaced mode %s\n",
 			 interlaced ? "on" : "off");
diff --git a/drivers/gpu/drm/sun4i/sun8i_mixer.h b/drivers/gpu/drm/sun4i/sun8i_mixer.h
index ebfc276b2464..bc12c95af6f3 100644
--- a/drivers/gpu/drm/sun4i/sun8i_mixer.h
+++ b/drivers/gpu/drm/sun4i/sun8i_mixer.h
@@ -65,6 +65,7 @@
 #define SUN8I_MIXER_BLEND_ROUTE_PIPE_MSK(n)	(0xf << ((n) << 2))
 #define SUN8I_MIXER_BLEND_ROUTE_PIPE_SHIFT(n)	((n) << 2)
 
+#define SUN8I_MIXER_BLEND_OUTCTL_PREMULTIPLY	BIT(0)
 #define SUN8I_MIXER_BLEND_OUTCTL_INTERLACED	BIT(1)
 
 #define SUN50I_MIXER_BLEND_CSC_CTL_EN(ch)	BIT(ch)
-- 
2.30.2