Commit bb6c19f7 authored by Daniel Stone's avatar Daniel Stone

compositor-drm: Add test-only mode to state application

The atomic API can allow us to test state before we apply it, to see if
it will be valid. Use this when we construct a plane configuration, to
see if it has a chance of ever working. If not, we can fail
assign_planes early.

This will be used in later patches to incrementally build state by
proposing and testing potential configurations one at a time.
Signed-off-by: Daniel Stone's avatarDaniel Stone <>
Reviewed-by: Pekka Paalanen's avatarPekka Paalanen <>
parent f829062e
......@@ -260,6 +260,7 @@ enum drm_output_state_duplicate_mode {
enum drm_state_apply_mode {
DRM_STATE_APPLY_SYNC, /**< state fully processed */
DRM_STATE_APPLY_ASYNC, /**< state pending event delivery */
DRM_STATE_TEST_ONLY, /**< test if the state can be applied */
struct drm_backend {
......@@ -1822,6 +1823,7 @@ drm_pending_state_get_output(struct drm_pending_state *pending_state,
static int drm_pending_state_apply_sync(struct drm_pending_state *state);
static int drm_pending_state_test(struct drm_pending_state *state);
* Mark a drm_output_state (the output's last state) as complete. This handles
......@@ -2610,9 +2612,20 @@ drm_pending_state_apply_atomic(struct drm_pending_state *pending_state,
ret = drmModeAtomicCommit(b->drm.fd, req, flags, b);
/* Test commits do not take ownership of the state; return
* without freeing here. */
if (mode == DRM_STATE_TEST_ONLY) {
return ret;
if (ret != 0) {
weston_log("atomic: couldn't commit new state: %m\n");
goto out;
......@@ -2633,6 +2646,40 @@ out:
* Tests a pending state, to see if the kernel will accept the update as
* constructed.
* Using atomic modesetting, the kernel performs the same checks as it would
* on a real commit, returning success or failure without actually modifying
* the running state. It does not return -EBUSY if there are pending updates
* in flight, so states may be tested at any point, however this means a
* state which passed testing may fail on a real commit if the timing is not
* respected (e.g. committing before the previous commit has completed).
* Without atomic modesetting, we have no way to check, so we optimistically
* claim it will work.
* Unlike drm_pending_state_apply() and drm_pending_state_apply_sync(), this
* function does _not_ take ownership of pending_state, nor does it clear
* state_invalid.
static int
drm_pending_state_test(struct drm_pending_state *pending_state)
struct drm_backend *b = pending_state->backend;
if (b->atomic_modeset)
return drm_pending_state_apply_atomic(pending_state,
/* We have no way to test state before application on the legacy
* modesetting API, so just claim it succeeded. */
return 0;
* Applies all of a pending_state asynchronously: the primary entry point for
* applying KMS state to a device. Updates the state for all outputs in the
......@@ -3271,6 +3318,7 @@ drm_output_propose_state(struct weston_output *output_base,
struct weston_view *ev;
pixman_region32_t surface_overlap, renderer_region, occluded_region;
bool planes_ok = (mode != DRM_OUTPUT_PROPOSE_STATE_RENDERER_ONLY);
int ret;
state = drm_output_state_duplicate(output->state_cur,
......@@ -3388,7 +3436,16 @@ drm_output_propose_state(struct weston_output *output_base,
/* Check to see if this state will actually work. */
ret = drm_pending_state_test(state->pending_state);
if (ret != 0)
goto err;
return state;
return NULL;
static void
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