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>
> + 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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