Alpha formats in DRM are assumed to be premultiplied, so we should be
setting the PREMULT bit in the plane configuration for HVS.

Signed-off-by: Stefan Schake <stsch...@gmail.com>
---
 drivers/gpu/drm/vc4/vc4_plane.c | 3 ++-
 drivers/gpu/drm/vc4/vc4_regs.h  | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
index c4c7af1..3d0c8a2 100644
--- a/drivers/gpu/drm/vc4/vc4_plane.c
+++ b/drivers/gpu/drm/vc4/vc4_plane.c
@@ -618,13 +618,14 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
                                              SCALER_POS1_SCL_HEIGHT));
        }
 
-       /* Position Word 2: Source Image Size, Alpha Mode */
+       /* Position Word 2: Source Image Size, Alpha */
        vc4_state->pos2_offset = vc4_state->dlist_count;
        vc4_dlist_write(vc4_state,
                        VC4_SET_FIELD(fb->format->has_alpha ?
                                      SCALER_POS2_ALPHA_MODE_PIPELINE :
                                      SCALER_POS2_ALPHA_MODE_FIXED,
                                      SCALER_POS2_ALPHA_MODE) |
+                       (format->has_alpha ? SCALER_POS2_ALPHA_PREMULT : 0) |
                        VC4_SET_FIELD(vc4_state->src_w[0], SCALER_POS2_WIDTH) |
                        VC4_SET_FIELD(vc4_state->src_h[0], SCALER_POS2_HEIGHT));
 
diff --git a/drivers/gpu/drm/vc4/vc4_regs.h b/drivers/gpu/drm/vc4/vc4_regs.h
index b9749cb..a141496 100644
--- a/drivers/gpu/drm/vc4/vc4_regs.h
+++ b/drivers/gpu/drm/vc4/vc4_regs.h
@@ -848,6 +848,7 @@ enum hvs_pixel_format {
 #define SCALER_POS2_ALPHA_MODE_FIXED           1
 #define SCALER_POS2_ALPHA_MODE_FIXED_NONZERO   2
 #define SCALER_POS2_ALPHA_MODE_FIXED_OVER_0x07 3
+#define SCALER_POS2_ALPHA_PREMULT              BIT(29)
 
 #define SCALER_POS2_HEIGHT_MASK                        VC4_MASK(27, 16)
 #define SCALER_POS2_HEIGHT_SHIFT               16
-- 
2.7.4

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