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drm: Peek at the current counter/timestamp for vblank queries 

Bypass all the spinlocks and return the last timestamp and counter from
the last vblank if the driver delcares that it is accurate (and stable
across on/off), and the vblank is currently enabled.

This is dependent upon the both the hardware and driver to provide the
proper barriers to facilitate reading our bookkeeping outside of the
vblank interrupt and outside of the explicit vblank locks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Michel Dänzer <michel@daenzer.net>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Dave Airlie <airlied@redhat.com>,
Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170317202030.24410-4-chris@chris-wilson.co.uk
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
This commit is contained in:
Chris Wilson 2017-03-17 20:20:30 +00:00 committed by Ville Syrjälä
parent 9a4d9babce
commit b33b02707b
1 changed files with 26 additions and 0 deletions
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26
drivers/gpu/drm/drm_irq.c
View File

@ -1561,6 +1561,17 @@ err_put:
return ret;
}
static bool drm_wait_vblank_is_query(union drm_wait_vblank *vblwait)
{
if (vblwait->request.sequence)
return false;
return _DRM_VBLANK_RELATIVE ==
(vblwait->request.type & (_DRM_VBLANK_TYPES_MASK |
_DRM_VBLANK_EVENT |
_DRM_VBLANK_NEXTONMISS));
}
/*
* Wait for VBLANK.
*
@ -1610,6 +1621,21 @@ int drm_wait_vblank(struct drm_device *dev, void *data,
vblank = &dev->vblank[pipe];
/* If the counter is currently enabled and accurate, short-circuit
* queries to return the cached timestamp of the last vblank.
*/
if (dev->vblank_disable_immediate &&
drm_wait_vblank_is_query(vblwait) &&
READ_ONCE(vblank->enabled)) {
struct timeval now;
vblwait->reply.sequence =
drm_vblank_count_and_time(dev, pipe, &now);
vblwait->reply.tval_sec = now.tv_sec;
vblwait->reply.tval_usec = now.tv_usec;
return 0;
}
ret = drm_vblank_get(dev, pipe);
if (ret) {
DRM_DEBUG("crtc %d failed to acquire vblank counter, %d\n", pipe, ret);