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>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -31,6 +31,7 @@
 #include <linux/slab.h>
 #include "drmP.h"
 #include "drm.h"
+#include "intel_drv.h"
 #include "i915_drm.h"
 #include "i915_drv.h"
 
@@ -121,6 +122,54 @@ static int i915_gem_object_list_info(struct seq_file *m, void *data)
 	return 0;
 }
 
+static int i915_gem_pageflip_info(struct seq_file *m, void *data)
+{
+	struct drm_info_node *node = (struct drm_info_node *) m->private;
+	struct drm_device *dev = node->minor->dev;
+	unsigned long flags;
+	struct intel_crtc *crtc;
+
+	list_for_each_entry(crtc, &dev->mode_config.crtc_list, base.head) {
+		const char *pipe = crtc->pipe ? "B" : "A";
+		const char *plane = crtc->plane ? "B" : "A";
+		struct intel_unpin_work *work;
+
+		spin_lock_irqsave(&dev->event_lock, flags);
+		work = crtc->unpin_work;
+		if (work == NULL) {
+			seq_printf(m, "No flip due on pipe %s (plane %s)\n",
+				   pipe, plane);
+		} else {
+			if (!work->pending) {
+				seq_printf(m, "Flip queued on pipe %s (plane %s)\n",
+					   pipe, plane);
+			} else {
+				seq_printf(m, "Flip pending (waiting for vsync) on pipe %s (plane %s)\n",
+					   pipe, plane);
+			}
+			if (work->enable_stall_check)
+				seq_printf(m, "Stall check enabled, ");
+			else
+				seq_printf(m, "Stall check waiting for page flip ioctl, ");
+			seq_printf(m, "%d prepares\n", work->pending);
+
+			if (work->old_fb_obj) {
+				struct drm_i915_gem_object *obj_priv = to_intel_bo(work->old_fb_obj);
+				if(obj_priv)
+					seq_printf(m, "Old framebuffer gtt_offset 0x%08x\n", obj_priv->gtt_offset );
+			}
+			if (work->pending_flip_obj) {
+				struct drm_i915_gem_object *obj_priv = to_intel_bo(work->pending_flip_obj);
+				if(obj_priv)
+					seq_printf(m, "New framebuffer gtt_offset 0x%08x\n", obj_priv->gtt_offset );
+			}
+		}
+		spin_unlock_irqrestore(&dev->event_lock, flags);
+	}
+
+	return 0;
+}
+
 static int i915_gem_request_info(struct seq_file *m, void *data)
 {
 	struct drm_info_node *node = (struct drm_info_node *) m->private;
@@ -777,6 +826,7 @@ static struct drm_info_list i915_debugfs_list[] = {
 	{"i915_gem_active", i915_gem_object_list_info, 0, (void *) ACTIVE_LIST},
 	{"i915_gem_flushing", i915_gem_object_list_info, 0, (void *) FLUSHING_LIST},
 	{"i915_gem_inactive", i915_gem_object_list_info, 0, (void *) INACTIVE_LIST},
+	{"i915_gem_pageflip", i915_gem_pageflip_info, 0},
 	{"i915_gem_request", i915_gem_request_info, 0},
 	{"i915_gem_seqno", i915_gem_seqno_info, 0},
 	{"i915_gem_fence_regs", i915_gem_fence_regs_info, 0},

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) ||

drivers/gpu/drm/i915/intel_display.c

@@ -4864,15 +4864,6 @@ static void intel_crtc_destroy(struct drm_crtc *crtc)
 	kfree(intel_crtc);
 }
 
-struct intel_unpin_work {
-	struct work_struct work;
-	struct drm_device *dev;
-	struct drm_gem_object *old_fb_obj;
-	struct drm_gem_object *pending_flip_obj;
-	struct drm_pending_vblank_event *event;
-	int pending;
-};
-
 static void intel_unpin_work_fn(struct work_struct *__work)
 {
 	struct intel_unpin_work *work =
@@ -4960,7 +4951,8 @@ void intel_prepare_page_flip(struct drm_device *dev, int plane)
 
 	spin_lock_irqsave(&dev->event_lock, flags);
 	if (intel_crtc->unpin_work) {
-		intel_crtc->unpin_work->pending = 1;
+		if ((++intel_crtc->unpin_work->pending) > 1)
+			DRM_ERROR("Prepared flip multiple times\n");
 	} else {
 		DRM_DEBUG_DRIVER("preparing flip with no unpin work?\n");
 	}
@@ -5044,6 +5036,8 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 		ADVANCE_LP_RING();
 	}
 
+	work->enable_stall_check = true;
+
 	/* Offset into the new buffer for cases of shared fbs between CRTCs */
 	offset = crtc->y * fb->pitch + crtc->x * fb->bits_per_pixel/8;
 

drivers/gpu/drm/i915/intel_drv.h

@@ -176,6 +176,16 @@ struct intel_crtc {
 #define enc_to_intel_encoder(x) container_of(x, struct intel_encoder, enc)
 #define to_intel_framebuffer(x) container_of(x, struct intel_framebuffer, base)
 
+struct intel_unpin_work {
+	struct work_struct work;
+	struct drm_device *dev;
+	struct drm_gem_object *old_fb_obj;
+	struct drm_gem_object *pending_flip_obj;
+	struct drm_pending_vblank_event *event;
+	int pending;
+	bool enable_stall_check;
+};
+
 struct i2c_adapter *intel_i2c_create(struct drm_device *dev, const u32 reg,
 				     const char *name);
 void intel_i2c_destroy(struct i2c_adapter *adapter);