redonkable/alistair23-linux
redonkable/alistair23-linux
1
0
Fork 0
Code Releases Activity

drm: Only update final vblank count when precise ts is available

Browse source 
Drivers without a hardware vblank counter simply can't account for the
vblanks that happened while the vblank interrupt was off. To check
this grab a vblank timestamp and if the result is dubious follow the
normal save-and-disable logic.

Drivers should prevent this by setting vblank_disable_allowed = false,
but since running vblank interrupts constantly is not good for power
consumption most drivers lie. Testing for precise vblank timestamps is
the next best thing we can check for.

Suggested-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
This commit is contained in:
Daniel Vetter 2014-09-10 17:36:09 +02:00
parent ab8905f1c6
commit 855d30b402
1 changed files with 8 additions and 1 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

9
drivers/gpu/drm/drm_irq.c
View file

@ -148,8 +148,15 @@ static void vblank_disable_and_save(struct drm_device *dev, int crtc)
* has been ticking all along until this time. This makes the
* count account for the entire time between drm_vblank_on() and
* drm_vblank_off().
*
* But only do this if precise vblank timestamps are available.
* Otherwise we might read a totally bogus timestamp since drivers
* lacking precise timestamp support rely upon sampling the system clock
* at vblank interrupt time. Which obviously won't work out well if the
* vblank interrupt is disabled.
*/
if (!vblank->enabled) {
if (!vblank->enabled &&
drm_get_last_vbltimestamp(dev, crtc, &tvblank, 0) > 0) {
drm_update_vblank_count(dev, crtc);
spin_unlock_irqrestore(&dev->vblank_time_lock, irqflags);
return;