[PATCH] drm: Don't zero vblank timestamps from the irq handler

[PATCH] drm: Don't zero vblank timestamps from the irq handler

[ville.syrjala]

From: Ville Syrjälä <ville.syrjala@linux.intel.com>

If we couldn't get a high precisions vblank timestamp, we currently
store a zeroed timestamp instead and assume the next vblank irq to
get us something better. This makes sense when trying to update the
timestamp from eg. vblank enable. But if we do this from the vblank
irq we will never get a vblank timestamp unless we high precision
timestamps are available and succeeded. This break weston for instance
on drivers lacking high precision timestamps.

To fix this, zero the timestamp only when not called from vbl irq.
When called from the irq, we still want the timestamp, even if not
perfect.

This fixes a regression from
4dfd64862ff852df drm: Use vblank timestamps to guesstimate how many vblanks were missed

Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Reported-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/drm_irq.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index f24c57c..1b9faa0 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -232,10 +232,11 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
 
 	/*
 	 * Only reinitialize corresponding vblank timestamp if high-precision query
-	 * available and didn't fail. Otherwise reinitialize delayed at next vblank
-	 * interrupt and assign 0 for now, to mark the vblanktimestamp as invalid.
+	 * available and didn't fail, or we were called from the vblank interrupt.
+	 * Otherwise reinitialize delayed at next vblank interrupt and assign 0
+	 * for now, to mark the vblanktimestamp as invalid.
 	 */
-	if (!rc)
+	if (!rc && (flags & DRM_CALLED_FROM_VBLIRQ) == 0)
 		t_vblank = (struct timeval) {0, 0};
 
 	store_vblank(dev, pipe, diff, &t_vblank, cur_vblank);
-- 
2.4.6

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Re: [PATCH] drm: Don't zero vblank timestamps from the irq handler

[Thierry Reding]

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On Wed, Sep 30, 2015 at 07:21:34PM +0300, ville.syrjala@linux.intel.com wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> If we couldn't get a high precisions vblank timestamp, we currently
> store a zeroed timestamp instead and assume the next vblank irq to
> get us something better. This makes sense when trying to update the
> timestamp from eg. vblank enable. But if we do this from the vblank
> irq we will never get a vblank timestamp unless we high precision
> timestamps are available and succeeded. This break weston for instance
> on drivers lacking high precision timestamps.
> 
> To fix this, zero the timestamp only when not called from vbl irq.
> When called from the irq, we still want the timestamp, even if not
> perfect.
> 
> This fixes a regression from
> 4dfd64862ff852df drm: Use vblank timestamps to guesstimate how many vblanks were missed
> 
> Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
> Cc: Thierry Reding <thierry.reding@gmail.com>
> Reported-by: Thierry Reding <thierry.reding@gmail.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/drm_irq.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Applied on top of next-20151001 and the weston problem I was seeing is
gone, so:

Tested-by: Thierry Reding <treding@nvidia.com>

I think it might be worth considering squashing this into the offending
commit to avoid breaking bisectibility.

Thierry

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Re: [PATCH] drm: Don't zero vblank timestamps from the irq handler

[Daniel Vetter]

On Thu, Oct 01, 2015 at 09:27:20AM +0200, Thierry Reding wrote:
> On Wed, Sep 30, 2015 at 07:21:34PM +0300, ville.syrjala@linux.intel.com wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > If we couldn't get a high precisions vblank timestamp, we currently
> > store a zeroed timestamp instead and assume the next vblank irq to
> > get us something better. This makes sense when trying to update the
> > timestamp from eg. vblank enable. But if we do this from the vblank
> > irq we will never get a vblank timestamp unless we high precision
> > timestamps are available and succeeded. This break weston for instance
> > on drivers lacking high precision timestamps.
> > 
> > To fix this, zero the timestamp only when not called from vbl irq.
> > When called from the irq, we still want the timestamp, even if not
> > perfect.
> > 
> > This fixes a regression from
> > 4dfd64862ff852df drm: Use vblank timestamps to guesstimate how many vblanks were missed
> > 
> > Cc: Mario Kleiner <mario.kleiner.de@gmail.com>
> > Cc: Thierry Reding <thierry.reding@gmail.com>
> > Reported-by: Thierry Reding <thierry.reding@gmail.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/drm_irq.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> Applied on top of next-20151001 and the weston problem I was seeing is
> gone, so:
> 
> Tested-by: Thierry Reding <treding@nvidia.com>
> 
> I think it might be worth considering squashing this into the offending
> commit to avoid breaking bisectibility.

Can't squash any more since history is frozen in drm-next. Applied to
drm-misc, thanks.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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