drm/i915: handle non-flip pending case when unpinning the scanout buffer

The first page flip queued will replace the current front buffer, which
should have a 0 pending flip count.  So at finish time we need to handle
that case (i.e. if the flip count is 0 *or* dec_and_test is 0 we need to
wake the waiters).

Also fix up an error path in the queue function and add some debug
output (only enabled with driver debugging).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

1 files changed, 18 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2cc489b6629e..5f14dfbf715c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3985,6 +3985,12 @@ void intel_finish_page_flip(struct drm_device *dev, int pipe)
         spin_lock_irqsave(&dev->event_lock, flags);
         work = intel_crtc->unpin_work;
         if (work == NULL || !work->pending) {
+                if (work && !work->pending) {
+                        obj_priv = work->obj->driver_private;
+                        DRM_DEBUG_DRIVER("flip finish: %p (%d) not pending?\n",
+                                         obj_priv,
+                                         atomic_read(&obj_priv->pending_flip));
+                }
                 spin_unlock_irqrestore(&dev->event_lock, flags);
                 return;
         }
@@ -4006,7 +4012,10 @@ void intel_finish_page_flip(struct drm_device *dev, int pipe)
         spin_unlock_irqrestore(&dev->event_lock, flags);
 
         obj_priv = work->obj->driver_private;
-        if (atomic_dec_and_test(&obj_priv->pending_flip))
+
+        /* Initial scanout buffer will have a 0 pending flip count */
+        if ((atomic_read(&obj_priv->pending_flip) == 0) ||
+            atomic_dec_and_test(&obj_priv->pending_flip))
                 DRM_WAKEUP(&dev_priv->pending_flip_queue);
         schedule_work(&work->work);
 }
@@ -4019,8 +4028,11 @@ void intel_prepare_page_flip(struct drm_device *dev, int plane)
         unsigned long flags;
 
         spin_lock_irqsave(&dev->event_lock, flags);
-        if (intel_crtc->unpin_work)
+        if (intel_crtc->unpin_work) {
                 intel_crtc->unpin_work->pending = 1;
+        } else {
+                DRM_DEBUG_DRIVER("preparing flip with no unpin work?\n");
+        }
         spin_unlock_irqrestore(&dev->event_lock, flags);
 }
 
@@ -4054,6 +4066,7 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
         /* We borrow the event spin lock for protecting unpin_work */
         spin_lock_irqsave(&dev->event_lock, flags);
         if (intel_crtc->unpin_work) {
+                DRM_DEBUG_DRIVER("flip queue: crtc already busy\n");
                 spin_unlock_irqrestore(&dev->event_lock, flags);
                 kfree(work);
                 mutex_unlock(&dev->struct_mutex);
@@ -4067,7 +4080,10 @@ static int intel_crtc_page_flip(struct drm_crtc *crtc,
 
         ret = intel_pin_and_fence_fb_obj(dev, obj);
         if (ret != 0) {
+                DRM_DEBUG_DRIVER("flip queue: %p pin & fence failed\n",
+                          obj->driver_private);
                 kfree(work);
+                intel_crtc->unpin_work = NULL;
                 mutex_unlock(&dev->struct_mutex);
                 return ret;
         }