[Intel-gfx] [PATCH] drm/i915: Make mmio flip wait for seqno in the work function

[Ander Conselvan de Oliveira]

This simplifies the code quite a bit compared to iterating over all
rings during the ring interrupt.

Also, it allows us to drop the mmio_flip spinlock, since the mmio_flip
struct is only accessed in two places. The first is when the flip is
queued and the other when the mmio writes are done. Since a flip cannot
be queued while there is a pending flip, the two paths shouldn't ever
run in parallel. We might need to revisit that if support for replacing
flips is implemented though.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira at intel.com>
---

I'm not sure if locking dev->struct_mutex in the work function might
have any ill effects, so I'd appreciate if someone could enlighten me.

Thanks,
Ander

---
 drivers/gpu/drm/i915/i915_irq.c      |  3 --
 drivers/gpu/drm/i915/intel_display.c | 91 +++++-------------------------------
 drivers/gpu/drm/i915/intel_drv.h     |  9 +---
 3 files changed, 13 insertions(+), 90 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 318a6a0..5fff287 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -979,9 +979,6 @@ static void notify_ring(struct drm_device *dev,
 
 	trace_i915_gem_request_complete(ring);
 
-	if (drm_core_check_feature(dev, DRIVER_MODESET))
-		intel_notify_mmio_flip(ring);
-
 	wake_up_all(&ring->irq_queue);
 	i915_queue_hangcheck(dev);
 }
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index f3ff8e8..24cfe19 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9424,73 +9424,25 @@ static void intel_do_mmio_flip(struct intel_crtc *intel_crtc)
 
 	if (atomic_update)
 		intel_pipe_update_end(intel_crtc, start_vbl_count);
-
-	spin_lock_irq(&dev_priv->mmio_flip_lock);
-	intel_crtc->mmio_flip.status = INTEL_MMIO_FLIP_IDLE;
-	spin_unlock_irq(&dev_priv->mmio_flip_lock);
 }
 
 static void intel_mmio_flip_work_func(struct work_struct *work)
 {
 	struct intel_crtc *intel_crtc =
 		container_of(work, struct intel_crtc, mmio_flip.work);
-
-	intel_do_mmio_flip(intel_crtc);
-}
-
-static int intel_postpone_flip(struct drm_i915_gem_object *obj)
-{
 	struct intel_engine_cs *ring;
-	int ret;
-
-	lockdep_assert_held(&obj->base.dev->struct_mutex);
-
-	if (!obj->last_write_seqno)
-		return 0;
-
-	ring = obj->ring;
+	uint32_t seqno;
 
-	if (i915_seqno_passed(ring->get_seqno(ring, true),
-			      obj->last_write_seqno))
-		return 0;
-
-	ret = i915_gem_check_olr(ring, obj->last_write_seqno);
-	if (ret)
-		return ret;
-
-	if (WARN_ON(!ring->irq_get(ring)))
-		return 0;
+	seqno = intel_crtc->mmio_flip.seqno;
+	ring = intel_crtc->mmio_flip.ring;
 
-	return 1;
-}
-
-void intel_notify_mmio_flip(struct intel_engine_cs *ring)
-{
-	struct drm_i915_private *dev_priv = to_i915(ring->dev);
-	struct intel_crtc *intel_crtc;
-	unsigned long irq_flags;
-	u32 seqno;
-
-	seqno = ring->get_seqno(ring, false);
-
-	spin_lock_irqsave(&dev_priv->mmio_flip_lock, irq_flags);
-	for_each_intel_crtc(ring->dev, intel_crtc) {
-		struct intel_mmio_flip *mmio_flip;
-
-		mmio_flip = &intel_crtc->mmio_flip;
-		if (mmio_flip->status != INTEL_MMIO_FLIP_WAIT_RING)
-			continue;
-
-		if (ring->id != mmio_flip->ring_id)
-			continue;
-
-		if (i915_seqno_passed(seqno, mmio_flip->seqno)) {
-			schedule_work(&intel_crtc->mmio_flip.work);
-			mmio_flip->status = INTEL_MMIO_FLIP_WORK_SCHEDULED;
-			ring->irq_put(ring);
-		}
+	if (seqno) {
+		mutex_lock(&ring->dev->struct_mutex);
+		WARN_ON(i915_wait_seqno(ring, seqno) != 0);
+		mutex_unlock(&ring->dev->struct_mutex);
 	}
-	spin_unlock_irqrestore(&dev_priv->mmio_flip_lock, irq_flags);
+
+	intel_do_mmio_flip(intel_crtc);
 }
 
 static int intel_queue_mmio_flip(struct drm_device *dev,
@@ -9500,32 +9452,13 @@ static int intel_queue_mmio_flip(struct drm_device *dev,
 				 struct intel_engine_cs *ring,
 				 uint32_t flags)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
-	int ret;
-
-	if (WARN_ON(intel_crtc->mmio_flip.status != INTEL_MMIO_FLIP_IDLE))
-		return -EBUSY;
-
-	ret = intel_postpone_flip(obj);
-	if (ret < 0)
-		return ret;
-	if (ret == 0) {
-		intel_do_mmio_flip(intel_crtc);
-		return 0;
-	}
 
-	spin_lock_irq(&dev_priv->mmio_flip_lock);
-	intel_crtc->mmio_flip.status = INTEL_MMIO_FLIP_WAIT_RING;
 	intel_crtc->mmio_flip.seqno = obj->last_write_seqno;
-	intel_crtc->mmio_flip.ring_id = obj->ring->id;
-	spin_unlock_irq(&dev_priv->mmio_flip_lock);
+	intel_crtc->mmio_flip.ring = obj->ring;
+
+	schedule_work(&intel_crtc->mmio_flip.work);
 
-	/*
-	 * Double check to catch cases where irq fired before
-	 * mmio flip data was ready
-	 */
-	intel_notify_mmio_flip(obj->ring);
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index c8ddde6..492d346 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -399,16 +399,9 @@ struct intel_pipe_wm {
 	bool sprites_scaled;
 };
 
-enum intel_mmio_flip_status {
-	INTEL_MMIO_FLIP_IDLE = 0,
-	INTEL_MMIO_FLIP_WAIT_RING,
-	INTEL_MMIO_FLIP_WORK_SCHEDULED,
-};
-
 struct intel_mmio_flip {
 	u32 seqno;
-	u32 ring_id;
-	enum intel_mmio_flip_status status;
+	struct intel_engine_cs *ring;
 	struct work_struct work;
 };
 
-- 
1.8.3.2