[PATCH 2/3] drm/vc4: Check if plane requires background fill

[Stefan Schake]

Considering a single plane only, we have to enable background color
when the plane has an alpha format and could be blending from the
background or when it doesn't cover the entire screen.

Signed-off-by: Stefan Schake <stschake at gmail.com>
---
 drivers/gpu/drm/vc4/vc4_drv.h   |  6 ++++++
 drivers/gpu/drm/vc4/vc4_plane.c | 15 ++++++++++++++-
 2 files changed, 20 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
index fefa166..7cc6390 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -302,6 +302,12 @@ struct vc4_hvs {
 
 struct vc4_plane {
 	struct drm_plane base;
+
+	/* Set when the plane has per-pixel alpha content or does not cover
+	 * the entire screen. This is a hint to the CRTC that it might need
+	 * to enable background color fill.
+	 */
+	bool needs_bg_fill;
 };
 
 static inline struct vc4_plane *
diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
index 3d0c8a2..c299e29 100644
--- a/drivers/gpu/drm/vc4/vc4_plane.c
+++ b/drivers/gpu/drm/vc4/vc4_plane.c
@@ -517,10 +517,12 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
 {
 	struct vc4_dev *vc4 = to_vc4_dev(plane->dev);
 	struct vc4_plane_state *vc4_state = to_vc4_plane_state(state);
+	struct vc4_plane *vc4_plane = to_vc4_plane(plane);
 	struct drm_framebuffer *fb = state->fb;
 	u32 ctl0_offset = vc4_state->dlist_count;
 	const struct hvs_format *format = vc4_get_hvs_format(fb->format->format);
 	int num_planes = drm_format_num_planes(format->drm);
+	bool covers_screen;
 	u32 scl0, scl1, pitch0;
 	u32 lbm_size, tiling;
 	unsigned long irqflags;
@@ -625,7 +627,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
 				      SCALER_POS2_ALPHA_MODE_PIPELINE :
 				      SCALER_POS2_ALPHA_MODE_FIXED,
 				      SCALER_POS2_ALPHA_MODE) |
-			(format->has_alpha ? SCALER_POS2_ALPHA_PREMULT : 0) |
+			(fb->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));
 
@@ -701,6 +703,17 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
 	vc4_state->dlist[ctl0_offset] |=
 		VC4_SET_FIELD(vc4_state->dlist_count, SCALER_CTL0_SIZE);
 
+	/* crtc_* are already clipped coordinates. */
+	covers_screen = vc4_state->crtc_x == 0 && vc4_state->crtc_y == 0 &&
+			vc4_state->crtc_w == state->crtc->mode.hdisplay &&
+			vc4_state->crtc_h == state->crtc->mode.vdisplay;
+	/* Background fill might be necessary when the plane has per-pixel
+	 * alpha content and blends from the background or does not cover
+	 * the entire screen.
+	 */
+	vc4_plane->needs_bg_fill = fb->format->has_alpha || !covers_screen;
+
+
 	return 0;
 }
 
-- 
2.7.4