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drm/sun4i: backend: Check for the number of alpha planes

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Due to the way the composition is done in hardware, we can only have a
single alpha-enabled plane active at a time, placed in the second (highest
priority) pipe.

Make sure of that in our atomic_check to not end up in an impossible
scenario.

Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Link: https://patchwork.freedesktop.org/patch/msgid/7371f62a1385f2cbe3ed75dfca2e746338eb2286.1516617243.git-series.maxime.ripard@free-electrons.com
This commit is contained in:
Maxime Ripard 2017-06-26 22:51:15 +02:00
parent 47a05f4a68
commit 65f7fa3a3f
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GPG Key ID: D2B4C094214DAF74
3 changed files with 55 additions and 22 deletions
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51
drivers/gpu/drm/sun4i/sun4i_backend.c
View File

@ -328,6 +328,8 @@ static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
struct drm_atomic_state *state = crtc_state->state;
struct drm_device *drm = state->dev;
struct drm_plane *plane;
unsigned int num_planes = 0;
unsigned int num_alpha_planes = 0;
unsigned int num_frontend_planes = 0;
DRM_DEBUG_DRIVER("Starting checking our planes\n");
@ -340,6 +342,8 @@ static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
drm_atomic_get_plane_state(state, plane);
struct sun4i_layer_state *layer_state =
state_to_sun4i_layer_state(plane_state);
struct drm_framebuffer *fb = plane_state->fb;
struct drm_format_name_buf format_name;
if (sun4i_backend_plane_uses_frontend(plane_state)) {
DRM_DEBUG_DRIVER("Using the frontend for plane %d\n",
@ -350,6 +354,50 @@ static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
} else {
layer_state->uses_frontend = false;
}
DRM_DEBUG_DRIVER("Plane FB format is %s\n",
drm_get_format_name(fb->format->format,
&format_name));
if (fb->format->has_alpha)
num_alpha_planes++;
num_planes++;
}
/*
* The hardware is a bit unusual here.
*
* Even though it supports 4 layers, it does the composition
* in two separate steps.
*
* The first one is assigning a layer to one of its two
* pipes. If more that 1 layer is assigned to the same pipe,
* and if pixels overlaps, the pipe will take the pixel from
* the layer with the highest priority.
*
* The second step is the actual alpha blending, that takes
* the two pipes as input, and uses the eventual alpha
* component to do the transparency between the two.
*
* This two steps scenario makes us unable to guarantee a
* robust alpha blending between the 4 layers in all
* situations, since this means that we need to have one layer
* with alpha at the lowest position of our two pipes.
*
* However, we cannot even do that, since the hardware has a
* bug where the lowest plane of the lowest pipe (pipe 0,
* priority 0), if it has any alpha, will discard the pixel
* entirely and just display the pixels in the background
* color (black by default).
*
* This means that we effectively have only three valid
* configurations with alpha, all of them with the alpha being
* on pipe1 with the lowest position, which can be 1, 2 or 3
* depending on the number of planes and their zpos.
*/
if (num_alpha_planes > SUN4I_BACKEND_NUM_ALPHA_LAYERS) {
DRM_DEBUG_DRIVER("Too many planes with alpha, rejecting...\n");
return -EINVAL;
}
if (num_frontend_planes > SUN4I_BACKEND_NUM_FRONTEND_LAYERS) {
@ -357,6 +405,9 @@ static int sun4i_backend_atomic_check(struct sunxi_engine *engine,
return -EINVAL;
}
DRM_DEBUG_DRIVER("State valid with %u planes, %u alpha, %u video\n",
num_planes, num_alpha_planes, num_frontend_planes);
return 0;
}

2
drivers/gpu/drm/sun4i/sun4i_backend.h
View File

@ -146,6 +146,8 @@
#define SUN4I_BACKEND_HWCCOLORTAB_OFF 0x4c00
#define SUN4I_BACKEND_PIPE_OFF(p) (0x5000 + (0x400 * (p)))
#define SUN4I_BACKEND_NUM_LAYERS 4
#define SUN4I_BACKEND_NUM_ALPHA_LAYERS 1
#define SUN4I_BACKEND_NUM_FRONTEND_LAYERS 1
struct sun4i_backend {

24
drivers/gpu/drm/sun4i/sun4i_layer.c
View File

@ -201,32 +201,12 @@ struct drm_plane **sun4i_layers_init(struct drm_device *drm,
struct sun4i_backend *backend = engine_to_sun4i_backend(engine);
int i;
planes = devm_kcalloc(drm->dev, ARRAY_SIZE(sun4i_backend_planes) + 1,
/* We need to have a sentinel at the need, hence the overallocation */
planes = devm_kcalloc(drm->dev, SUN4I_BACKEND_NUM_LAYERS + 1,
sizeof(*planes), GFP_KERNEL);
if (!planes)
return ERR_PTR(-ENOMEM);
/*
* The hardware is a bit unusual here.
*
* Even though it supports 4 layers, it does the composition
* in two separate steps.
*
* The first one is assigning a layer to one of its two
* pipes. If more that 1 layer is assigned to the same pipe,
* and if pixels overlaps, the pipe will take the pixel from
* the layer with the highest priority.
*
* The second step is the actual alpha blending, that takes
* the two pipes as input, and uses the eventual alpha
* component to do the transparency between the two.
*
* This two steps scenario makes us unable to guarantee a
* robust alpha blending between the 4 layers in all
* situations. So we just expose two layers, one per pipe. On
* SoCs that support it, sprites could fill the need for more
* layers.
*/
for (i = 0; i < ARRAY_SIZE(sun4i_backend_planes); i++) {
const struct sun4i_plane_desc *plane = &sun4i_backend_planes[i];
struct sun4i_layer *layer;