drm: Always reject drm_vblank_get() after drm_vblank_off()

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Make sure drm_vblank_get() never succeeds when called between
drm_vblank_off() and drm_vblank_on(). Borrow a trick from the
old drm_vblank_{pre,post}_modeset() functions and just bump
the refcount in drm_vblank_off() and drop it in drm_vblank_on().

When drm_vblank_get() encounters a >0 refcount and the vblank
interrupt is already disabled it will simply return -EINVAL.

Hopefully the use of inmodeset won't conflict badly with
drm_vblank_{pre,post}_modeset().

For i915 there's a window between drm_vblank_off() and marking the
crtc as inactive where the current code still allows drm_vblank_get().

v2: Describe what drm_vblank_get() does to explain how
    a simple refcount bump manages to fix things (Daniel)

Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

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Ville Syrjälä 2014-08-06 14:49:44 +03:00 • committed by Daniel Vetter

parent 21d70354bb

commit 7ffd7a6851

1 changed files with 14 additions and 0 deletions

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drivers/gpu/drm/drm_irq.c

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