On 02/09/2016 10:54 AM, Daniel Vetter wrote:
On Mon, Feb 08, 2016 at 02:13:24AM +0100, Mario Kleiner wrote: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. 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. Signed-off-by: Mario Kleiner <mario.kleiner.de@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> # 4.4+ Cc: michel@xxxxxxxxxxx Cc: vbabka@xxxxxxx Cc: ville.syrjala@xxxxxxxxxxxxxxx Cc: daniel.vetter@xxxxxxxx Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Cc: alexander.deucher@xxxxxxx Cc: christian.koenig@xxxxxxx --- drivers/gpu/drm/drm_irq.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index 607f493..bcb8528 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -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 (!vblank->inmodeset)Since atomic drivers shouldn't suck so badly at this, maybe if (DRIVER_ATOMIC || !vblank->inmodeset) instead? That way the flexibility would be constraint to old drivers that need it because legacy crtc helpers suck. With that change: Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
Ok, thanks, will change that. -mario
+ 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); -- 1.9.1
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