drm/i915: Check for a stalled page flip after each vblank

Long ago, back in the racy haydays of 915gm interrupt handling, page
flips would occasionally go astray and leave the hardware stuck, and the
display not updating. This annoyed people who relied on their systems
being able to display continuously updating information 24/7, and so
some code to detect when the driver missed the page flip completion
signal was added. Until recently, it was presumed that the interrupt
handling was now flawless, but once again Simon Farnsworth has found a
system whose display will stall. Reinstate the pageflip stall detection,
which works by checking to see if the hardware has been updated to the
new framebuffer address following each vblank. If the hardware is
scanning out from the new framebuffer, but we still think the flip is
pending, then we kick our driver into submision.

This is a continuation of the effort started with
commit 4e5359cd053bfb7d8dabe4a63624a5726848ffbc
Author: Simon Farnsworth <simon.farnsworth@onelan.co.uk>
Date:   Wed Sep 1 17:47:52 2010 +0100

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

This now includes a belt-and-braces approach to make sure the driver
(or the hardware) doesn't miss an interrupt and cause us to stop
updating the display should the unthinkable happen and the pageflip fail - i.e.
that the user is able to continue submitting flips.

v2: Cleanup, refactor, and rename
v3: Only start counting vblanks after the flip command has been seen by
    the hardware.
v4: Record the seqno after we touch the ring, or else there may be no
    seqno allocated yet.
v5: Rebase on mmio-flip.
v6: Rebase, rebase.

Reported-by: Simon Farnsworth <simon@farnz.org.uk>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75502
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com> [v4]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 24 insertions, 60 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 66b5cca8b880..9f097537bbc9 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2087,8 +2087,9 @@ static void valleyview_pipestat_irq_handler(struct drm_device *dev, u32 iir)
 	spin_unlock(&dev_priv->irq_lock);
 
 	for_each_pipe(dev_priv, pipe) {
-		if (pipe_stats[pipe] & PIPE_START_VBLANK_INTERRUPT_STATUS)
-			intel_pipe_handle_vblank(dev, pipe);
+		if (pipe_stats[pipe] & PIPE_START_VBLANK_INTERRUPT_STATUS &&
+		    intel_pipe_handle_vblank(dev, pipe))
+			intel_check_page_flip(dev, pipe);
 
 		if (pipe_stats[pipe] & PLANE_FLIP_DONE_INT_STATUS_VLV) {
 			intel_prepare_page_flip(dev, pipe);
@@ -2387,8 +2388,9 @@ static void ilk_display_irq_handler(struct drm_device *dev, u32 de_iir)
 		DRM_ERROR("Poison interrupt\n");
 
 	for_each_pipe(dev_priv, pipe) {
-		if (de_iir & DE_PIPE_VBLANK(pipe))
-			intel_pipe_handle_vblank(dev, pipe);
+		if (de_iir & DE_PIPE_VBLANK(pipe) &&
+		    intel_pipe_handle_vblank(dev, pipe))
+			intel_check_page_flip(dev, pipe);
 
 		if (de_iir & DE_PIPE_FIFO_UNDERRUN(pipe))
 			if (intel_set_cpu_fifo_underrun_reporting(dev, pipe, false))
@@ -2437,8 +2439,9 @@ static void ivb_display_irq_handler(struct drm_device *dev, u32 de_iir)
 		intel_opregion_asle_intr(dev);
 
 	for_each_pipe(dev_priv, pipe) {
-		if (de_iir & (DE_PIPE_VBLANK_IVB(pipe)))
-			intel_pipe_handle_vblank(dev, pipe);
+		if (de_iir & (DE_PIPE_VBLANK_IVB(pipe)) &&
+		    intel_pipe_handle_vblank(dev, pipe))
+			intel_check_page_flip(dev, pipe);
 
 		/* plane/pipes map 1:1 on ilk+ */
 		if (de_iir & DE_PLANE_FLIP_DONE_IVB(pipe)) {
@@ -2593,8 +2596,9 @@ static irqreturn_t gen8_irq_handler(int irq, void *arg)
 		if (pipe_iir) {
 			ret = IRQ_HANDLED;
 			I915_WRITE(GEN8_DE_PIPE_IIR(pipe), pipe_iir);
-			if (pipe_iir & GEN8_PIPE_VBLANK)
-				intel_pipe_handle_vblank(dev, pipe);
+			if (pipe_iir & GEN8_PIPE_VBLANK &&
+			    intel_pipe_handle_vblank(dev, pipe))
+				intel_check_page_flip(dev, pipe);
 
 			if (pipe_iir & GEN8_PIPE_PRIMARY_FLIP_DONE) {
 				intel_prepare_page_flip(dev, pipe);
@@ -2899,52 +2903,6 @@ void i915_handle_error(struct drm_device *dev, bool wedged,
 	schedule_work(&dev_priv->gpu_error.work);
 }
 
-static void __always_unused i915_pageflip_stall_check(struct drm_device *dev, int pipe)
-{
-	struct drm_i915_private *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;
-	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 ||
-	    atomic_read(&work->pending) >= INTEL_FLIP_COMPLETE ||
-	    !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 = work->pending_flip_obj;
-	if (INTEL_INFO(dev)->gen >= 4) {
-		int dspsurf = DSPSURF(intel_crtc->plane);
-		stall_detected = I915_HI_DISPBASE(I915_READ(dspsurf)) ==
-					i915_gem_obj_ggtt_offset(obj);
-	} else {
-		int dspaddr = DSPADDR(intel_crtc->plane);
-		stall_detected = I915_READ(dspaddr) == (i915_gem_obj_ggtt_offset(obj) +
-							crtc->y * crtc->primary->fb->pitches[0] +
-							crtc->x * crtc->primary->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);
-	}
-}
-
 /* Called from drm generic code, passed 'crtc' which
  * we use as a pipe index
  */
@@ -4082,7 +4040,7 @@ static bool i8xx_handle_vblank(struct drm_device *dev,
 		return false;
 
 	if ((iir & flip_pending) == 0)
-		return false;
+		goto check_page_flip;
 
 	intel_prepare_page_flip(dev, plane);
 
@@ -4093,11 +4051,14 @@ static bool i8xx_handle_vblank(struct drm_device *dev,
 	 * an interrupt per se, we watch for the change at vblank.
 	 */
 	if (I915_READ16(ISR) & flip_pending)
-		return false;
+		goto check_page_flip;
 
 	intel_finish_page_flip(dev, pipe);
-
 	return true;
+
+check_page_flip:
+	intel_check_page_flip(dev, pipe);
+	return false;
 }
 
 static irqreturn_t i8xx_irq_handler(int irq, void *arg)
@@ -4267,7 +4228,7 @@ static bool i915_handle_vblank(struct drm_device *dev,
 		return false;
 
 	if ((iir & flip_pending) == 0)
-		return false;
+		goto check_page_flip;
 
 	intel_prepare_page_flip(dev, plane);
 
@@ -4278,11 +4239,14 @@ static bool i915_handle_vblank(struct drm_device *dev,
 	 * an interrupt per se, we watch for the change at vblank.
 	 */
 	if (I915_READ(ISR) & flip_pending)
-		return false;
+		goto check_page_flip;
 
 	intel_finish_page_flip(dev, pipe);
-
 	return true;
+
+check_page_flip:
+	intel_check_page_flip(dev, pipe);
+	return false;
 }
 
 static irqreturn_t i915_irq_handler(int irq, void *arg)