drm: Limit the number of .get_vblank_counter() retries

Pontential infinite loops in the vblank code are a bad idea. Add some
limits.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 0353224..93fe582 100644 (file)
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -127,6 +127,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
        u32 cur_vblank, diff;
        bool rc;
        struct timeval t_vblank;
+       int count = DRM_TIMESTAMP_MAXRETRIES;
 
        /*
         * Interrupts were disabled prior to this call, so deal with counter
@@ -143,7 +144,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
        do {
                cur_vblank = dev->driver->get_vblank_counter(dev, pipe);
                rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, flags);
-       } while (cur_vblank != dev->driver->get_vblank_counter(dev, pipe));
+       } while (cur_vblank != dev->driver->get_vblank_counter(dev, pipe) && --count > 0);
 
        /* Deal with counter wrap */
        diff = cur_vblank - vblank->last;
@@ -914,6 +915,7 @@ u32 drm_vblank_count_and_time(struct drm_device *dev, unsigned int pipe,
                              struct timeval *vblanktime)
 {
        struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+       int count = DRM_TIMESTAMP_MAXRETRIES;
        u32 cur_vblank;
 
        if (WARN_ON(pipe >= dev->num_crtcs))
@@ -929,7 +931,7 @@ u32 drm_vblank_count_and_time(struct drm_device *dev, unsigned int pipe,
                smp_rmb();
                *vblanktime = vblanktimestamp(dev, pipe, cur_vblank);
                smp_rmb();
-       } while (cur_vblank != vblank->count);
+       } while (cur_vblank != vblank->count && --count > 0);
 
        return cur_vblank;
 }