2017-05-31 Eric Anholt eric@anholt.net:
Gustavo Padovan gustavo@padovan.org writes:
From: Gustavo Padovan gustavo.padovan@collabora.com
In some cases, like cursor updates, it is interesting to update the plane in an asynchronous fashion to avoid big delays. The current queued update could be still waiting for a fence to signal and thus block any subsequent update until its scan out. In cases like this if we update the cursor synchronously through the atomic API it will cause significant delays that would even be noticed by the final user.
This patch creates a fast path to jump ahead the current queued state and do single planes updates without going through all atomic steps in drm_atomic_helper_commit(). We take this path for legacy cursor updates.
For now only single plane updates are supported, but we plan to support multiple planes updates and async PageFlips through this interface as well in the near future.
Sorry for taking so long to do some review for this.
drivers/gpu/drm/drm_atomic.c | 65 ++++++++++++++++++++++++++++++++ drivers/gpu/drm/drm_atomic_helper.c | 35 +++++++++++++++++ include/drm/drm_atomic.h | 2 + include/drm/drm_atomic_helper.h | 2 + include/drm/drm_modeset_helper_vtables.h | 48 +++++++++++++++++++++++ 5 files changed, 152 insertions(+)
diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c index be62774..2a0c297 100644 --- a/drivers/gpu/drm/drm_atomic.c +++ b/drivers/gpu/drm/drm_atomic.c @@ -631,6 +631,68 @@ static int drm_atomic_crtc_check(struct drm_crtc *crtc, return 0; }
+static bool drm_atomic_async_check(struct drm_atomic_state *state) +{
- struct drm_crtc *crtc;
- struct drm_crtc_state *crtc_state;
- struct drm_crtc_commit *commit;
- struct drm_plane *__plane, *plane = NULL;
- struct drm_plane_state *__plane_state, *plane_state = NULL;
- const struct drm_plane_helper_funcs *funcs;
- int i, j, n_planes = 0;
- for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
if (drm_atomic_crtc_needs_modeset(crtc_state))return false;- }
- for_each_new_plane_in_state(state, __plane, __plane_state, i) {
n_planes++;plane = __plane;plane_state = __plane_state;- }
- /* FIXME: we support only single plane updates for now */
- if (!plane || n_planes != 1)
return false;- if (!plane_state->crtc)
return false;- funcs = plane->helper_private;
- if (!funcs->atomic_async_update)
return false;- if (plane_state->fence)
return false;Could you add a comment here like:
/* Don't do an async update if there is an outstanding commit modifying
- the plane. This prevents our async update's changes from getting
- overridden by a previous synchronous update's state.
*/
(assuming I understand its intent correctly)
I don't understand KMS locking enough to say if this loop is actually safely guaranteeing that. If you're convinced of that, then with my little cleanups this patch will be:
I'm going to check the locking again just to make sure.
Acked-by: Eric Anholt eric@anholt.net
- for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
if (plane->crtc != crtc)continue;spin_lock(&crtc->commit_lock);commit = list_first_entry_or_null(&crtc->commit_list,struct drm_crtc_commit,commit_entry);if (!commit) {spin_unlock(&crtc->commit_lock);continue;}spin_unlock(&crtc->commit_lock);if (!crtc->state->state)continue;for_each_plane_in_state(crtc->state->state, __plane,__plane_state, j) {if (__plane == plane)return false;}- }
- return !funcs->atomic_async_check(plane, plane_state);
+}
static void drm_atomic_crtc_print_state(struct drm_printer *p, const struct drm_crtc_state *state) { @@ -1591,6 +1653,9 @@ int drm_atomic_check_only(struct drm_atomic_state *state) } }
- if (state->legacy_cursor_update)
state->async_update = drm_atomic_async_check(state);- return ret;
} EXPORT_SYMBOL(drm_atomic_check_only); diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c index 5a3c9c0..a8efdfe 100644 --- a/drivers/gpu/drm/drm_atomic_helper.c +++ b/drivers/gpu/drm/drm_atomic_helper.c @@ -1235,6 +1235,30 @@ static void commit_work(struct work_struct *work) }
/**
- drm_atomic_helper_async_commit - commit state asynchronously
- This function commits a state asynchronously, i.e., not vblank
- synchronized. It should be used on a state only when
- drm_atomic_async_check() succeeds. Async commits are not supposed to swap
- the states like normal sync commits, but just do in-place changes on the
- current state.
- */
+void drm_atomic_helper_async_commit(struct drm_device *dev,
struct drm_atomic_state *state)+{
- struct drm_plane *plane;
- struct drm_plane_state *plane_state;
- const struct drm_plane_helper_funcs *funcs;
- int i;
- for_each_new_plane_in_state(state, plane, plane_state, i) {
funcs = plane->helper_private;funcs->atomic_async_update(plane, plane_state);- }
+} +EXPORT_SYMBOL(drm_atomic_helper_async_commit);
+/**
- drm_atomic_helper_commit - commit validated state object
- @dev: DRM device
- @state: the driver state object
@@ -1258,6 +1282,17 @@ int drm_atomic_helper_commit(struct drm_device *dev, { int ret;
- if (state->async_update) {
ret = drm_atomic_helper_prepare_planes(dev, state);if (ret)return ret;drm_atomic_helper_async_commit(dev, state);drm_atomic_helper_cleanup_planes(dev, state);return 0;- }
- ret = drm_atomic_helper_setup_commit(state, nonblock); if (ret) return ret;
diff --git a/include/drm/drm_atomic.h b/include/drm/drm_atomic.h index 788daf7..70ca279 100644 --- a/include/drm/drm_atomic.h +++ b/include/drm/drm_atomic.h @@ -160,6 +160,7 @@ struct __drm_connnectors_state {
- @dev: parent DRM device
- @allow_modeset: allow full modeset
- @legacy_cursor_update: hint to enforce legacy cursor IOCTL semantics
- @async_update: hint for asynchronous plane update
- @planes: pointer to array of structures with per-plane data
- @crtcs: pointer to array of CRTC pointers
- @num_connector: size of the @connectors and @connector_states arrays
@@ -172,6 +173,7 @@ struct drm_atomic_state { struct drm_device *dev; bool allow_modeset : 1; bool legacy_cursor_update : 1;
- bool async_update : 1; struct __drm_planes_state *planes; struct __drm_crtcs_state *crtcs; int num_connector;
diff --git a/include/drm/drm_atomic_helper.h b/include/drm/drm_atomic_helper.h index f0a8678..8571b51 100644 --- a/include/drm/drm_atomic_helper.h +++ b/include/drm/drm_atomic_helper.h @@ -44,6 +44,8 @@ void drm_atomic_helper_commit_tail(struct drm_atomic_state *state); int drm_atomic_helper_commit(struct drm_device *dev, struct drm_atomic_state *state, bool nonblock); +void drm_atomic_helper_async_commit(struct drm_device *dev,
struct drm_atomic_state *state);int drm_atomic_helper_wait_for_fences(struct drm_device *dev, struct drm_atomic_state *state, diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h index c01c328..7964a78 100644 --- a/include/drm/drm_modeset_helper_vtables.h +++ b/include/drm/drm_modeset_helper_vtables.h @@ -1048,6 +1048,54 @@ struct drm_plane_helper_funcs { */ void (*atomic_disable)(struct drm_plane *plane, struct drm_plane_state *old_state);
- /**
* @atomic_async_check:** Drivers should set this function pointer to check if the plane state* can be updated in a async fashion. Here async means "not vblank* synchronized".** This hook is called by drm_atomic_async_check() to establish if a* given update can be committed asynchronously, that is, if it can* jump ahead the state currently queued for update.** RETURNS:** Return 0 on success and any error returned indicates that the update* can not be applied in asynchronous manner.*/- int (*atomic_async_check)(struct drm_plane *plane,
struct drm_plane_state *state);- /**
* @atomic_async_update:** Drivers should set this function pointer to perform asynchronous* updates of planes, that is, jump ahead the currently queued"jump ahead of the"
* state for and update the plane. Here async means "not vblanks/for //
* synchronized".** This hook is called by drm_atomic_helper_async_commit().** An async update will happen on legacy cursor updates.** Note that unlike &drm_plane_helper_funcs.atomic_update this hook* takes the new &drm_plane_state as parameter. When doing async_update* drivers shouldn't replace the &drm_plane_state but update the* current one with the new plane configurations in the new* plane_state.Also maybe document that this won't be called if there is an outstanding commit modifying the plane?
** FIXME:* - It only works for single plane updates* - Async Pageflips are not supported yet* - Some hm might still scan out the old buffer until the next"Some hw"?
* vblank, however we let go of the fb references as soon as* we run this hook. For now drivers must implement their own workers* for defering if needed, until a common solution is created.*/"deferring"
- void (*atomic_async_update)(struct drm_plane *plane,
struct drm_plane_state *new_state);Is there a simple list of what parts of drm_plane_state may change in this hook? I noticed that vc4 wasn't checking that the format doesn't change, for example. I'm also not sure if we're guaranteed that the plane-is-enabled state isn't changing, either.
I can look into building such a list. I'll do that and send a proposed one here.
If it's "everything", we'll need to improve the vc4 async check before we expose this under anything but the cursor ioctl.
Gustavo