Commit 57c08294 authored by Mario Kleiner's avatar Mario Kleiner Committed by Greg Kroah-Hartman

drm: No-Op redundant calls to drm_vblank_off() (v2)

commit e8235891 upstream.

Otherwise if a kms driver calls into drm_vblank_off() more than once
before calling drm_vblank_on() again, the redundant calls to
vblank_disable_and_save() will call drm_update_vblank_count()
while hw vblank counters and vblank timestamping are in a undefined
state during modesets, dpms off etc.

At least with the legacy drm helpers it is not unusual to
get multiple calls to drm_vblank_off and drm_vblank_on, e.g.,
half a dozen calls to drm_vblank_off and two calls to drm_vblank_on
were observed on radeon-kms during dpms-off -> dpms-on transition.

We don't no-op calls from atomic modesetting drivers, as they
should do a proper job of tracking hw state.

Fixes large jumps of the software maintained vblank counter due to
the hardware vblank counter resetting to zero during dpms off or
modeset, e.g., if radeon-kms is modified to use drm_vblank_off/on
instead of drm_vblank_pre/post_modeset().

This fixes a regression caused by the changes made to
drm_update_vblank_count() in Linux 4.4.

v2: Don't no-op on atomic modesetting drivers, per suggestion
    of Daniel Vetter.
Signed-off-by: default avatarMario Kleiner <mario.kleiner.de@gmail.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Cc: michel@daenzer.net
Cc: vbabka@suse.cz
Cc: ville.syrjala@linux.intel.com
Cc: alexander.deucher@amd.com
Cc: christian.koenig@amd.com
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 96e87f46
......@@ -1313,7 +1313,13 @@ void drm_vblank_off(struct drm_device *dev, unsigned int pipe)
spin_lock_irqsave(&dev->event_lock, irqflags);
spin_lock(&dev->vbl_lock);
vblank_disable_and_save(dev, pipe);
DRM_DEBUG_VBL("crtc %d, vblank enabled %d, inmodeset %d\n",
pipe, vblank->enabled, vblank->inmodeset);
/* Avoid redundant vblank disables without previous drm_vblank_on(). */
if (drm_core_check_feature(dev, DRIVER_ATOMIC) || !vblank->inmodeset)
vblank_disable_and_save(dev, pipe);
wake_up(&vblank->queue);
/*
......@@ -1415,6 +1421,9 @@ void drm_vblank_on(struct drm_device *dev, unsigned int pipe)
return;
spin_lock_irqsave(&dev->vbl_lock, irqflags);
DRM_DEBUG_VBL("crtc %d, vblank enabled %d, inmodeset %d\n",
pipe, vblank->enabled, vblank->inmodeset);
/* Drop our private "prevent drm_vblank_get" refcount */
if (vblank->inmodeset) {
atomic_dec(&vblank->refcount);
......
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