drm/msm: async commit support

Now that flush/wait/complete is decoupled from the "synchronous" part of
atomic commit_tail(), add support to defer flush to a timer that expires
shortly before vblank for async commits.  In this way, multiple atomic
commits (for example, cursor updates) can be coalesced into a single
flush at the end of the frame.

v2: don't hold lock over ->wait_flush(), to avoid locking interaction
    that was causing fps drop when combining page flips or non-async
    atomic commits and lots of legacy cursor updates
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Sean Paul <sean@poorly.run>

drivers/gpu/drm/msm/msm_atomic.c

@@ -26,6 +26,95 @@ int msm_atomic_prepare_fb(struct drm_plane *plane,
 	return msm_framebuffer_prepare(new_state->fb, kms->aspace);
 }
 
+static void msm_atomic_async_commit(struct msm_kms *kms, int crtc_idx)
+{
+	unsigned crtc_mask = BIT(crtc_idx);
+
+	mutex_lock(&kms->commit_lock);
+
+	if (!(kms->pending_crtc_mask & crtc_mask)) {
+		mutex_unlock(&kms->commit_lock);
+		return;
+	}
+
+	kms->pending_crtc_mask &= ~crtc_mask;
+
+	kms->funcs->enable_commit(kms);
+
+	/*
+	 * Flush hardware updates:
+	 */
+	DRM_DEBUG_ATOMIC("triggering async commit\n");
+	kms->funcs->flush_commit(kms, crtc_mask);
+	mutex_unlock(&kms->commit_lock);
+
+	/*
+	 * Wait for flush to complete:
+	 */
+	kms->funcs->wait_flush(kms, crtc_mask);
+
+	mutex_lock(&kms->commit_lock);
+	kms->funcs->complete_commit(kms, crtc_mask);
+	mutex_unlock(&kms->commit_lock);
+	kms->funcs->disable_commit(kms);
+}
+
+static enum hrtimer_restart msm_atomic_pending_timer(struct hrtimer *t)
+{
+	struct msm_pending_timer *timer = container_of(t,
+			struct msm_pending_timer, timer);
+	struct msm_drm_private *priv = timer->kms->dev->dev_private;
+
+	queue_work(priv->wq, &timer->work);
+
+	return HRTIMER_NORESTART;
+}
+
+static void msm_atomic_pending_work(struct work_struct *work)
+{
+	struct msm_pending_timer *timer = container_of(work,
+			struct msm_pending_timer, work);
+
+	msm_atomic_async_commit(timer->kms, timer->crtc_idx);
+}
+
+void msm_atomic_init_pending_timer(struct msm_pending_timer *timer,
+		struct msm_kms *kms, int crtc_idx)
+{
+	timer->kms = kms;
+	timer->crtc_idx = crtc_idx;
+	hrtimer_init(&timer->timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS);
+	timer->timer.function = msm_atomic_pending_timer;
+	INIT_WORK(&timer->work, msm_atomic_pending_work);
+}
+
+static bool can_do_async(struct drm_atomic_state *state,
+		struct drm_crtc **async_crtc)
+{
+	struct drm_connector_state *connector_state;
+	struct drm_connector *connector;
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *crtc;
+	int i, num_crtcs = 0;
+
+	if (!(state->legacy_cursor_update || state->async_update))
+		return false;
+
+	/* any connector change, means slow path: */
+	for_each_new_connector_in_state(state, connector, connector_state, i)
+		return false;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		if (drm_atomic_crtc_needs_modeset(crtc_state))
+			return false;
+		if (++num_crtcs > 1)
+			return false;
+		*async_crtc = crtc;
+	}
+
+	return true;
+}
+
 /* Get bitmask of crtcs that will need to be flushed.  The bitmask
  * can be used with for_each_crtc_mask() iterator, to iterate
  * effected crtcs without needing to preserve the atomic state.
@@ -47,9 +136,25 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
 	struct drm_device *dev = state->dev;
 	struct msm_drm_private *priv = dev->dev_private;
 	struct msm_kms *kms = priv->kms;
+	struct drm_crtc *async_crtc = NULL;
 	unsigned crtc_mask = get_crtc_mask(state);
+	bool async = kms->funcs->vsync_time &&
+			can_do_async(state, &async_crtc);
 
 	kms->funcs->enable_commit(kms);
+
+	/*
+	 * Ensure any previous (potentially async) commit has
+	 * completed:
+	 */
+	kms->funcs->wait_flush(kms, crtc_mask);
+
+	mutex_lock(&kms->commit_lock);
+
+	/*
+	 * Now that there is no in-progress flush, prepare the
+	 * current update:
+	 */
 	kms->funcs->prepare_commit(kms, state);
 
 	/*
@@ -59,6 +164,49 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
 	drm_atomic_helper_commit_planes(dev, state, 0);
 	drm_atomic_helper_commit_modeset_enables(dev, state);
 
+	if (async) {
+		struct msm_pending_timer *timer =
+			&kms->pending_timers[drm_crtc_index(async_crtc)];
+
+		/* async updates are limited to single-crtc updates: */
+		WARN_ON(crtc_mask != drm_crtc_mask(async_crtc));
+
+		/*
+		 * Start timer if we don't already have an update pending
+		 * on this crtc:
+		 */
+		if (!(kms->pending_crtc_mask & crtc_mask)) {
+			ktime_t vsync_time, wakeup_time;
+
+			kms->pending_crtc_mask |= crtc_mask;
+
+			vsync_time = kms->funcs->vsync_time(kms, async_crtc);
+			wakeup_time = ktime_sub(vsync_time, ms_to_ktime(1));
+
+			hrtimer_start(&timer->timer, wakeup_time,
+					HRTIMER_MODE_ABS);
+		}
+
+		kms->funcs->disable_commit(kms);
+		mutex_unlock(&kms->commit_lock);
+
+		/*
+		 * At this point, from drm core's perspective, we
+		 * are done with the atomic update, so we can just
+		 * go ahead and signal that it is done:
+		 */
+		drm_atomic_helper_commit_hw_done(state);
+		drm_atomic_helper_cleanup_planes(dev, state);
+
+		return;
+	}
+
+	/*
+	 * If there is any async flush pending on updated crtcs, fold
+	 * them into the current flush.
+	 */
+	kms->pending_crtc_mask &= ~crtc_mask;
+
 	/*
 	 * Flush hardware updates:
 	 */
@@ -67,12 +215,18 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
 		kms->funcs->commit(kms, state);
 	}
 	kms->funcs->flush_commit(kms, crtc_mask);
+	mutex_unlock(&kms->commit_lock);
 
+	/*
+	 * Wait for flush to complete:
+	 */
 	kms->funcs->wait_flush(kms, crtc_mask);
+
+	mutex_lock(&kms->commit_lock);
 	kms->funcs->complete_commit(kms, crtc_mask);
+	mutex_unlock(&kms->commit_lock);
 	kms->funcs->disable_commit(kms);
 
 	drm_atomic_helper_commit_hw_done(state);
-
 	drm_atomic_helper_cleanup_planes(dev, state);
 }

drivers/gpu/drm/msm/msm_drv.c

@@ -473,6 +473,7 @@ static int msm_drm_init(struct device *dev, struct drm_driver *drv)
 	ddev->mode_config.normalize_zpos = true;
 
 	if (kms) {
+		kms->dev = ddev;
 		ret = kms->funcs->hw_init(kms);
 		if (ret) {
 			DRM_DEV_ERROR(dev, "kms hw init failed: %d\n", ret);

drivers/gpu/drm/msm/msm_drv.h

@@ -221,8 +221,12 @@ struct msm_format {
 	uint32_t pixel_format;
 };
 
+struct msm_pending_timer;
+
 int msm_atomic_prepare_fb(struct drm_plane *plane,
 			  struct drm_plane_state *new_state);
+void msm_atomic_init_pending_timer(struct msm_pending_timer *timer,
+		struct msm_kms *kms, int crtc_idx);
 void msm_atomic_commit_tail(struct drm_atomic_state *state);
 struct drm_atomic_state *msm_atomic_state_alloc(struct drm_device *dev);
 void msm_atomic_state_clear(struct drm_atomic_state *state);

drivers/gpu/drm/msm/msm_kms.h

@@ -33,6 +33,20 @@ struct msm_kms_funcs {
 
 	/*
 	 * Atomic commit handling:
+	 *
+	 * Note that in the case of async commits, the funcs which take
+	 * a crtc_mask (ie. ->flush_commit(), and ->complete_commit())
+	 * might not be evenly balanced with ->prepare_commit(), however
+	 * each crtc that effected by a ->prepare_commit() (potentially
+	 * multiple times) will eventually (at end of vsync period) be
+	 * flushed and completed.
+	 *
+	 * This has some implications about tracking of cleanup state,
+	 * for example SMP blocks to release after commit completes.  Ie.
+	 * cleanup state should be also duplicated in the various
+	 * duplicate_state() methods, as the current cleanup state at
+	 * ->complete_commit() time may have accumulated cleanup work
+	 * from multiple commits.
 	 */
 
 	/**
@@ -45,6 +59,14 @@ struct msm_kms_funcs {
 	void (*enable_commit)(struct msm_kms *kms);
 	void (*disable_commit)(struct msm_kms *kms);
 
+	/**
+	 * If the kms backend supports async commit, it should implement
+	 * this method to return the time of the next vsync.  This is
+	 * used to determine a time slightly before vsync, for the async
+	 * commit timer to run and complete an async commit.
+	 */
+	ktime_t (*vsync_time)(struct msm_kms *kms, struct drm_crtc *crtc);
+
 	/**
 	 * Prepare for atomic commit.  This is called after any previous
 	 * (async or otherwise) commit has completed.
@@ -109,20 +131,48 @@ struct msm_kms_funcs {
 #endif
 };
 
+struct msm_kms;
+
+/*
+ * A per-crtc timer for pending async atomic flushes.  Scheduled to expire
+ * shortly before vblank to flush pending async updates.
+ */
+struct msm_pending_timer {
+	struct hrtimer timer;
+	struct work_struct work;
+	struct msm_kms *kms;
+	unsigned crtc_idx;
+};
+
 struct msm_kms {
 	const struct msm_kms_funcs *funcs;
+	struct drm_device *dev;
 
 	/* irq number to be passed on to drm_irq_install */
 	int irq;
 
 	/* mapper-id used to request GEM buffer mapped for scanout: */
 	struct msm_gem_address_space *aspace;
+
+	/*
+	 * For async commit, where ->flush_commit() and later happens
+	 * from the crtc's pending_timer close to end of the frame:
+	 */
+	struct mutex commit_lock;
+	unsigned pending_crtc_mask;
+	struct msm_pending_timer pending_timers[MAX_CRTCS];
 };
 
 static inline void msm_kms_init(struct msm_kms *kms,
 		const struct msm_kms_funcs *funcs)
 {
+	unsigned i;
+
+	mutex_init(&kms->commit_lock);
 	kms->funcs = funcs;
+
+	for (i = 0; i < ARRAY_SIZE(kms->pending_timers); i++)
+		msm_atomic_init_pending_timer(&kms->pending_timers[i], kms, i);
 }
 
 struct msm_kms *mdp4_kms_init(struct drm_device *dev);