On 18.03.2015 11:53, Michel Dänzer wrote:
On 18.03.2015 00:44, Chris Wilson wrote:
When userspace queries the current vblank for the CRTC, we can reply with the cached value (using atomic reads to serialise with the vblank interrupt as necessary) without having to touch registers. In the instant disable case, this saves us from enabling/disabling the vblank around every query, greatly reducing the number of registers read and written.
Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Imre Deak imre.deak@intel.com Cc: Daniel Vetter daniel.vetter@intel.com Cc: Ville Syrjälä ville.syrjala@linux.intel.com Cc: Laurent Pinchart laurent.pinchart@ideasonboard.com Cc: Dave Airlie airlied@redhat.com
drivers/gpu/drm/drm_irq.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index c8a34476570a..6c4570082b65 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -1585,7 +1585,18 @@ int drm_wait_vblank(struct drm_device *dev, void *data, if (crtc >= dev->num_crtcs) return -EINVAL;
- vblank = &dev->vblank[crtc];
- /* Fast-path the query for the current value (without an event)
* to avoid having to enable/disable the vblank interrupts.*/- if ((vblwait->request.type & (_DRM_VBLANK_TYPES_MASK | _DRM_VBLANK_FLAGS_MASK)) == _DRM_VBLANK_RELATIVE &&
vblwait->request.sequence == 0) {struct timeval now;vblwait->reply.sequence = drm_vblank_count_and_time(dev, crtc, &now);vblwait->reply.tval_sec = now.tv_sec;vblwait->reply.tval_usec = now.tv_usec;return 0;- }
drm_vblank_count_and_time() doesn't return the correct sequence number while the vblank interrupt is disabled, does it? It returns the sequence number from the last time vblank_disable_and_save() was called (when the vblank interrupt was disabled). That's why drm_vblank_get() is needed here.
It might be possible to avoid drm_vblank_get() and use drm_update_vblank_count() before (or in) drm_vblank_count_and_time() instead when the vblank interrupt is disabled, but then you'd first need to make it safe to call drm_update_vblank_count() several times while the vblank interrupt is disabled, by making it update vblank->last at least.