Discussion:
[PATCH v2] drm/vc4: Add support for plane alpha
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Stefan Schake
2018-04-21 00:09:54 UTC
Permalink
The HVS supports mixing fixed alpha with per-pixel alpha or
setting a fixed plane alpha in case there is no per-pixel information.
This allows us to support the generic DRM plane alpha property.

Signed-off-by: Stefan Schake <***@gmail.com>
---
v2: Non-opaque plane alpha can trigger the background blending issue
and we need to hint the CRTC that background fill might be required.

drivers/gpu/drm/vc4/vc4_plane.c | 21 +++++++++++++++++----
drivers/gpu/drm/vc4/vc4_regs.h | 1 +
2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
index c3a37a99e601..3483c05cc3d6 100644
--- a/drivers/gpu/drm/vc4/vc4_plane.c
+++ b/drivers/gpu/drm/vc4/vc4_plane.c
@@ -201,6 +201,7 @@ static void vc4_plane_reset(struct drm_plane *plane)
return;

plane->state = &vc4_state->base;
+ plane->state->alpha = DRM_BLEND_ALPHA_OPAQUE;
vc4_state->base.plane = plane;
}

@@ -467,6 +468,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
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 mix_plane_alpha;
bool covers_screen;
u32 scl0, scl1, pitch0;
u32 lbm_size, tiling;
@@ -552,7 +554,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
/* Position Word 0: Image Positions and Alpha Value */
vc4_state->pos0_offset = vc4_state->dlist_count;
vc4_dlist_write(vc4_state,
- VC4_SET_FIELD(0xff, SCALER_POS0_FIXED_ALPHA) |
+ VC4_SET_FIELD(state->alpha >> 8, SCALER_POS0_FIXED_ALPHA) |
VC4_SET_FIELD(vc4_state->crtc_x, SCALER_POS0_START_X) |
VC4_SET_FIELD(vc4_state->crtc_y, SCALER_POS0_START_Y));

@@ -565,6 +567,13 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
SCALER_POS1_SCL_HEIGHT));
}

+ /* Don't waste cycles mixing with plane alpha if the set alpha
+ * is opaque or there is no per-pixel alpha information.
+ * In any case we use the alpha property value as the fixed alpha.
+ */
+ mix_plane_alpha = state->alpha != DRM_BLEND_ALPHA_OPAQUE &&
+ fb->format->has_alpha;
+
/* Position Word 2: Source Image Size, Alpha */
vc4_state->pos2_offset = vc4_state->dlist_count;
vc4_dlist_write(vc4_state,
@@ -572,6 +581,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
SCALER_POS2_ALPHA_MODE_PIPELINE :
SCALER_POS2_ALPHA_MODE_FIXED,
SCALER_POS2_ALPHA_MODE) |
+ (mix_plane_alpha ? SCALER_POS2_ALPHA_MIX : 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));
@@ -653,10 +663,11 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
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.
+ * alpha content or a non-opaque plane alpha and could blend from the
+ * background or does not cover the entire screen.
*/
- vc4_state->needs_bg_fill = fb->format->has_alpha || !covers_screen;
+ vc4_state->needs_bg_fill = fb->format->has_alpha || !covers_screen ||
+ state->alpha != DRM_BLEND_ALPHA_OPAQUE;

return 0;
}
@@ -916,5 +927,7 @@ struct drm_plane *vc4_plane_init(struct drm_device *dev,

drm_plane_helper_add(plane, &vc4_plane_helper_funcs);

+ drm_plane_create_alpha_property(plane);
+
return plane;
}
diff --git a/drivers/gpu/drm/vc4/vc4_regs.h b/drivers/gpu/drm/vc4/vc4_regs.h
index 4af3e29d076a..d1fb6fec46eb 100644
--- a/drivers/gpu/drm/vc4/vc4_regs.h
+++ b/drivers/gpu/drm/vc4/vc4_regs.h
@@ -945,6 +945,7 @@ enum hvs_pixel_format {
#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_ALPHA_MIX BIT(28)

#define SCALER_POS2_HEIGHT_MASK VC4_MASK(27, 16)
#define SCALER_POS2_HEIGHT_SHIFT 16
--
2.14.1
Eric Anholt
2018-04-23 18:27:57 UTC
Permalink
Post by Stefan Schake
The HVS supports mixing fixed alpha with per-pixel alpha or
setting a fixed plane alpha in case there is no per-pixel information.
This allows us to support the generic DRM plane alpha property.
Applied to drm-misc-next. Thanks!
Post by Stefan Schake
@@ -565,6 +567,13 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
SCALER_POS1_SCL_HEIGHT));
}
+ /* Don't waste cycles mixing with plane alpha if the set alpha
+ * is opaque or there is no per-pixel alpha information.
+ * In any case we use the alpha property value as the fixed alpha.
+ */
+ mix_plane_alpha = state->alpha != DRM_BLEND_ALPHA_OPAQUE &&
+ fb->format->has_alpha;
+
/* Position Word 2: Source Image Size, Alpha */
vc4_state->pos2_offset = vc4_state->dlist_count;
vc4_dlist_write(vc4_state,
@@ -572,6 +581,7 @@ static int vc4_plane_mode_set(struct drm_plane *plane,
SCALER_POS2_ALPHA_MODE_FIXED,
SCALER_POS2_ALPHA_MODE) |
+ (mix_plane_alpha ? SCALER_POS2_ALPHA_MIX : 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));
In an interesting note from the docs, if you'd set SCALER_POS2_ALPHA_MIX
with SCALER_POS2_ALPHA_MODE_FIXED, you'd get the fixed alpha squared!
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