drm/i915: Avoid pageflipping freeze when we miss the flip prepare interrupt

When we miss the flip prepare interrupt, we never get into the
software state needed to restart userspace, resulting in a freeze of a
full-screen OpenGL application (such as a compositor).

Work around this by checking DSPxSURF/DSPxBASE to see if the page flip
has actually happened. If it has, do the work we would have done when
the flip prepare interrupt comes in.

Also, add debugfs information to tell us what's going on (based on the
patch from Chris Wilson attached to bugs.fdo bug #29798).

Signed-off-by: Simon Farnsworth <simon.farnsworth@onelan.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 49 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 16861b800fee..59457e83b011 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -887,6 +887,49 @@ static void i915_handle_error(struct drm_device *dev, bool wedged)
 	queue_work(dev_priv->wq, &dev_priv->error_work);
 }
 
+static void i915_pageflip_stall_check(struct drm_device *dev, int pipe)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	struct drm_crtc *crtc = dev_priv->pipe_to_crtc_mapping[pipe];
+	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
+	struct drm_i915_gem_object *obj_priv;
+	struct intel_unpin_work *work;
+	unsigned long flags;
+	bool stall_detected;
+
+	/* Ignore early vblank irqs */
+	if (intel_crtc == NULL)
+		return;
+
+	spin_lock_irqsave(&dev->event_lock, flags);
+	work = intel_crtc->unpin_work;
+
+	if (work == NULL || work->pending || !work->enable_stall_check) {
+		/* Either the pending flip IRQ arrived, or we're too early. Don't check */
+		spin_unlock_irqrestore(&dev->event_lock, flags);
+		return;
+	}
+
+	/* Potential stall - if we see that the flip has happened, assume a missed interrupt */
+	obj_priv = to_intel_bo(work->pending_flip_obj);
+	if(IS_I965G(dev)) {
+		int dspsurf = intel_crtc->plane == 0 ? DSPASURF : DSPBSURF;
+		stall_detected = I915_READ(dspsurf) == obj_priv->gtt_offset;
+	} else {
+		int dspaddr = intel_crtc->plane == 0 ? DSPAADDR : DSPBADDR;
+		stall_detected = I915_READ(dspaddr) == (obj_priv->gtt_offset +
+							crtc->y * crtc->fb->pitch +
+							crtc->x * crtc->fb->bits_per_pixel/8);
+	}
+
+	spin_unlock_irqrestore(&dev->event_lock, flags);
+
+	if (stall_detected) {
+		DRM_DEBUG_DRIVER("Pageflip stall detected\n");
+		intel_prepare_page_flip(dev, intel_crtc->plane);
+	}
+}
+
 irqreturn_t i915_driver_irq_handler(DRM_IRQ_ARGS)
 {
 	struct drm_device *dev = (struct drm_device *) arg;
@@ -1004,15 +1047,19 @@ irqreturn_t i915_driver_irq_handler(DRM_IRQ_ARGS)
 		if (pipea_stats & vblank_status) {
 			vblank++;
 			drm_handle_vblank(dev, 0);
-			if (!dev_priv->flip_pending_is_done)
+			if (!dev_priv->flip_pending_is_done) {
+				i915_pageflip_stall_check(dev, 0);
 				intel_finish_page_flip(dev, 0);
+			}
 		}
 
 		if (pipeb_stats & vblank_status) {
 			vblank++;
 			drm_handle_vblank(dev, 1);
-			if (!dev_priv->flip_pending_is_done)
+			if (!dev_priv->flip_pending_is_done) {
+				i915_pageflip_stall_check(dev, 1);
 				intel_finish_page_flip(dev, 1);
+			}
 		}
 
 		if ((pipea_stats & PIPE_LEGACY_BLC_EVENT_STATUS) ||