On Wed, Sep 10, 2014 at 05:36:09PM +0200, Daniel Vetter wrote:
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 Signed-off-by: Daniel Vetter daniel.vetter@intel.com
Reviewed-by: Matt Roper matthew.d.roper@intel.com
drivers/gpu/drm/drm_irq.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 6eb015020af2..922721ead29a 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -163,8 +163,15 @@ 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) {-- 1.9.3