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drm/tegra: Don't use vblank_disable_immediate on incapable driver.

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Tegra would not only need a hardware vblank counter that
increments at leading edge of vblank, but also support
for instantaneous high precision vblank timestamp queries, ie.
a proper implementation of dev->driver->get_vblank_timestamp().

Without these, there can be off-by-one errors during vblank
disable/enable if the scanout is inside vblank at en/disable
time, and additionally clients will never see any useable
vblank timestamps when querying via drmWaitVblank ioctl. This
would negatively affect swap scheduling under X11 and Wayland.

Signed-off-by: Mario Kleiner <mario.kleiner.de@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
This commit is contained in:
Mario Kleiner 2015-05-04 06:29:44 +02:00 committed by Dave Airlie
parent 94754c183a
commit 3790e395b8
1 changed files with 0 additions and 1 deletions
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drivers/gpu/drm/tegra/drm.c
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@ -173,7 +173,6 @@ static int tegra_drm_load(struct drm_device *drm, unsigned long flags)
drm->irq_enabled = true;
/* syncpoints are used for full 32-bit hardware VBLANK counters */
drm->vblank_disable_immediate = true;
drm->max_vblank_count = 0xffffffff;
err = drm_vblank_init(drm, drm->mode_config.num_crtc);