diff options
author | Mario Kleiner <mario.kleiner.de@gmail.com> | 2013-10-30 05:13:06 +0100 |
---|---|---|
committer | Dave Airlie <airlied@redhat.com> | 2013-11-06 11:53:41 +1000 |
commit | 8f6fce03ddaf10bfa40c7d6cd59b778d35d41800 (patch) | |
tree | cada34e1587b003af267a75877e30caf60292779 /drivers/gpu/drm/drm_irq.c | |
parent | 862cc8b4bba9381c1824a0b7ed6404ec2cfb21b1 (diff) | |
download | op-kernel-dev-8f6fce03ddaf10bfa40c7d6cd59b778d35d41800.zip op-kernel-dev-8f6fce03ddaf10bfa40c7d6cd59b778d35d41800.tar.gz |
drm: Push latency sensitive bits of vblank scanoutpos timestamping into kms drivers.
A change in locking of some kms drivers (currently intel-kms) make
the old approach too inaccurate and also incompatible with the
PREEMPT_RT realtime kernel patchset.
The driver->get_scanout_position() method of intel-kms now needs
to aquire a spinlock, which clashes badly with the former
preempt_disable() calls in the drm, and it also introduces larger
delays and timing uncertainty on a contended lock than acceptable.
This patch changes the prototype of driver->get_scanout_position()
to require/allow kms drivers to perform the ktime_get() system time
queries which go along with actual scanout position readout in a way
that provides maximum precision and to return those timestamps to
the drm. kms drivers implementations of get_scanout_position() are
asked to implement timestamping and scanoutpos readout in a way
that is as precise as possible and compatible with preempt_disable()
on a PREMPT_RT kernel. A driver should follow this pattern in
get_scanout_position() for precision and compatibility:
spin_lock...(...);
preempt_disable_rt(); // On a PREEMPT_RT kernel, otherwise omit.
if (stime) *stime = ktime_get();
... Minimum amount of MMIO register reads to get scanout position ...
... no taking of locks allowed here! ...
if (etime) *etime = ktime_get();
preempt_enable_rt(); // On PREEMPT_RT kernel, otherwise omit.
spin_unlock...(...);
v2: Fix formatting of new multi-line code comments.
Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Diffstat (limited to 'drivers/gpu/drm/drm_irq.c')
-rw-r--r-- | drivers/gpu/drm/drm_irq.c | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 33ee515..d80d952 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -219,7 +219,7 @@ int drm_vblank_init(struct drm_device *dev, int num_crtcs) for (i = 0; i < num_crtcs; i++) init_waitqueue_head(&dev->vblank[i].queue); - DRM_INFO("Supports vblank timestamp caching Rev 1 (10.10.2010).\n"); + DRM_INFO("Supports vblank timestamp caching Rev 2 (21.10.2013).\n"); /* Driver specific high-precision vblank timestamping supported? */ if (dev->driver->get_vblank_timestamp) @@ -586,14 +586,17 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, int crtc, * code gets preempted or delayed for some reason. */ for (i = 0; i < DRM_TIMESTAMP_MAXRETRIES; i++) { - /* Get system timestamp before query. */ - stime = ktime_get(); - - /* Get vertical and horizontal scanout pos. vpos, hpos. */ - vbl_status = dev->driver->get_scanout_position(dev, crtc, &vpos, &hpos); + /* + * Get vertical and horizontal scanout position vpos, hpos, + * and bounding timestamps stime, etime, pre/post query. + */ + vbl_status = dev->driver->get_scanout_position(dev, crtc, &vpos, + &hpos, &stime, &etime); - /* Get system timestamp after query. */ - etime = ktime_get(); + /* + * Get correction for CLOCK_MONOTONIC -> CLOCK_REALTIME if + * CLOCK_REALTIME is requested. + */ if (!drm_timestamp_monotonic) mono_time_offset = ktime_get_monotonic_offset(); @@ -604,6 +607,7 @@ int drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev, int crtc, return -EIO; } + /* Compute uncertainty in timestamp of scanout position query. */ duration_ns = ktime_to_ns(etime) - ktime_to_ns(stime); /* Accept result with < max_error nsecs timing uncertainty. */ |