On Wed, Apr 15, 2015 at 11:25:00AM +0200, Daniel Vetter wrote:
On Wed, Apr 15, 2015 at 09:17:03AM +0100, Chris Wilson wrote:
On Wed, Apr 15, 2015 at 09:17:02AM +0200, Daniel Vetter wrote:
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index c8a34476570a..23bfbc61a494 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -74,6 +74,33 @@ module_param_named(vblankoffdelay, drm_vblank_offdelay, int, 0600); module_param_named(timestamp_precision_usec, drm_timestamp_precision, int, 0600); module_param_named(timestamp_monotonic, drm_timestamp_monotonic, int, 0600);
+static void store_vblank(struct drm_device *dev, int crtc,
unsigned vblank_count_inc,struct timeval *t_vblank)+{
- struct drm_vblank_crtc *vblank = &dev->vblank[crtc];
- u32 tslot;
- assert_spin_locked(&dev->vblank_time_lock);
- if (t_vblank) {
tslot = vblank->count + vblank_count_inc;vblanktimestamp(dev, crtc, tslot) = *t_vblank;- }
It is not obvious this updates the right tslot in all circumstances. Care to explain?
Writers are synchronized with vblank_time_lock, so there shouldn't be any races. Mario also has a patch to clear the ts slot if we don't have anything to set it too (that one will conflict ofc).
Or what exactly do you mean?
I was staring at vblank->count and reading backwards from the smp_wmb().
Just something like: if (t_vblank) { /* All writers hold the spinlock, but readers are serialized by * the latching of vblank->count below. */ u32 tslot = vblank->count + vblank_count_inc; ...
would help me understand the relationship better. -Chris