[01/15] drm/vblank: Allow dynamic per-crtc max_vblank_count

Commit Message

Ville Syrjälä Nov. 12, 2018, 4:59 p.m. UTC

From: Ville Syrjälä <[e-mail]>

On i965gm we need to adjust max_vblank_count dynamically
depending on whether the TV encoder is used or not. To
that end add a per-crtc max_vblank_count that takes
precedence over its device wide counterpart. The driver
can now call drm_crtc_set_max_vblank_count() to configure
the per-crtc value before calling drm_vblank_on().

Also looks like there was some discussion about exynos needing
similar treatment.

Cc: [e-mail]
Cc: Inki Dae <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Signed-off-by: Ville Syrjälä <[e-mail]>
---
 drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
 include/drm/drm_vblank.h     |  8 ++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)

Comments

Daniel Vetter Nov. 21, 2018, 9:27 a.m. UTC | #1

On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <[e-mail]>
> 
> On i965gm we need to adjust max_vblank_count dynamically
> depending on whether the TV encoder is used or not. To
> that end add a per-crtc max_vblank_count that takes
> precedence over its device wide counterpart. The driver
> can now call drm_crtc_set_max_vblank_count() to configure
> the per-crtc value before calling drm_vblank_on().
> 
> Also looks like there was some discussion about exynos needing
> similar treatment.
> 
> Cc: [e-mail]
> Cc: Inki Dae <[e-mail]>
> Cc: Daniel Vetter <[e-mail]>
> Signed-off-by: Ville Syrjälä <[e-mail]>
> ---
>  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
>  include/drm/drm_vblank.h     |  8 ++++++++
>  2 files changed, 43 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> index 98e091175921..c3abbdca8aba 100644
> --- a/drivers/gpu/drm/drm_vblank.c
> +++ b/drivers/gpu/drm/drm_vblank.c
> @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
>  	write_sequnlock(&vblank->seqlock);
>  }
>  
> +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> +{
> +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> +
> +	return vblank->max_vblank_count ?: dev->max_vblank_count;
> +}
> +
>  /*
>   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
>   * if there is no useable hardware frame counter available.
>   */
>  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
>  {
> -	WARN_ON_ONCE(dev->max_vblank_count != 0);
> +	WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
>  	return 0;
>  }
>  
> @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
>  	ktime_t t_vblank;
>  	int count = DRM_TIMESTAMP_MAXRETRIES;
>  	int framedur_ns = vblank->framedur_ns;
> +	u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
>  
>  	/*
>  	 * Interrupts were disabled prior to this call, so deal with counter
> @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
>  		rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
>  	} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
>  
> -	if (dev->max_vblank_count != 0) {
> +	if (max_vblank_count) {
>  		/* trust the hw counter when it's around */
> -		diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> +		diff = (cur_vblank - vblank->last) & max_vblank_count;
>  	} else if (rc && framedur_ns) {
>  		u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
>  
> @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
>  		      pipe, vblank->count, diff, cur_vblank, vblank->last);
>  
>  	if (diff == 0) {
> -		WARN_ON_ONCE(cur_vblank != vblank->last);
> +		WARN_ON_ONCE(max_vblank_count &&
> +			     cur_vblank != vblank->last);

Unrelated bugfix for this warning? Should be a separate patch I think, or
I'm missing something.

>  		return;
>  	}
>  
> @@ -1204,6 +1213,28 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
>  }
>  EXPORT_SYMBOL(drm_crtc_vblank_reset);
>  
> +/**
> + * drm_crtc_set_max_vblank_count - configure the hw max vblank counter value
> + * @crtc: CRTC in question
> + * @max_vblank_count: max hardware vblank counter value
> + *
> + * Update the maximum hardware vblank counter value for @crtc. Useful
> + * for hardware where the operation of the hardware vblank counter
> + * depends on the active display configuration.
> + *
> + * If used, must be called before drm_vblank_on().

I think we should check this at runtime with a WARN_ON. Plus make the
comment here a bit clearer that this is indeed for runtime adjusting of
the max_vblank_count, in cases where that depends upon the connected
outputs.

> + */
> +void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
> +				   u32 max_vblank_count)
> +{
> +	struct drm_device *dev = crtc->dev;
> +	unsigned int pipe = drm_crtc_index(crtc);
> +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> +
> +	vblank->max_vblank_count = max_vblank_count;
> +}
> +EXPORT_SYMBOL(drm_crtc_set_max_vblank_count);
> +
>  /**
>   * drm_crtc_vblank_on - enable vblank events on a CRTC
>   * @crtc: CRTC in question
> diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> index 6ad9630d4f48..ecb2cf9913e2 100644
> --- a/include/drm/drm_vblank.h
> +++ b/include/drm/drm_vblank.h
> @@ -128,6 +128,12 @@ struct drm_vblank_crtc {
>  	 * @last: Protected by &drm_device.vbl_lock, used for wraparound handling.
>  	 */
>  	u32 last;
> +	/**
> +	 * @max_vblank_count: Maximum value of the hardware vblank counter.
> +	 * If non-zero this takes precedence over &drm_device.max_vblank_count
> +	 * for this crtc. Otherwise &drm_device.max_vblank_count is used.
> +	 */

I'd add "This should be set by calling drm_crtc_set_max_vblank_count()."

And please also add a note to the kerneldoc of drm_driver.max_vblank_count
pointing at &drm_vblank_crtc.max_vblank_count for per-crtc limits.

Aside from the nits lgtm. I think I'll skip looking at the TV out stuff
though ...

Cheers, Daniel

> +	u32 max_vblank_count;
>  	/**
>  	 * @inmodeset: Tracks whether the vblank is disabled due to a modeset.
>  	 * For legacy driver bit 2 additionally tracks whether an additional
> @@ -206,4 +212,6 @@ bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
>  void drm_calc_timestamping_constants(struct drm_crtc *crtc,
>  				     const struct drm_display_mode *mode);
>  wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
> +void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
> +				   u32 max_vblank_count);
>  #endif
> -- 
> 2.18.1
>

Ville Syrjälä Nov. 21, 2018, 11:37 a.m. UTC | #2

On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <[e-mail]>
> > 
> > On i965gm we need to adjust max_vblank_count dynamically
> > depending on whether the TV encoder is used or not. To
> > that end add a per-crtc max_vblank_count that takes
> > precedence over its device wide counterpart. The driver
> > can now call drm_crtc_set_max_vblank_count() to configure
> > the per-crtc value before calling drm_vblank_on().
> > 
> > Also looks like there was some discussion about exynos needing
> > similar treatment.
> > 
> > Cc: [e-mail]
> > Cc: Inki Dae <[e-mail]>
> > Cc: Daniel Vetter <[e-mail]>
> > Signed-off-by: Ville Syrjälä <[e-mail]>
> > ---
> >  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> >  include/drm/drm_vblank.h     |  8 ++++++++
> >  2 files changed, 43 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > index 98e091175921..c3abbdca8aba 100644
> > --- a/drivers/gpu/drm/drm_vblank.c
> > +++ b/drivers/gpu/drm/drm_vblank.c
> > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> >  	write_sequnlock(&vblank->seqlock);
> >  }
> >  
> > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > +{
> > +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > +
> > +	return vblank->max_vblank_count ?: dev->max_vblank_count;
> > +}
> > +
> >  /*
> >   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> >   * if there is no useable hardware frame counter available.
> >   */
> >  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> >  {
> > -	WARN_ON_ONCE(dev->max_vblank_count != 0);
> > +	WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> >  	return 0;
> >  }
> >  
> > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> >  	ktime_t t_vblank;
> >  	int count = DRM_TIMESTAMP_MAXRETRIES;
> >  	int framedur_ns = vblank->framedur_ns;
> > +	u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> >  
> >  	/*
> >  	 * Interrupts were disabled prior to this call, so deal with counter
> > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> >  		rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> >  	} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> >  
> > -	if (dev->max_vblank_count != 0) {
> > +	if (max_vblank_count) {
> >  		/* trust the hw counter when it's around */
> > -		diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > +		diff = (cur_vblank - vblank->last) & max_vblank_count;
> >  	} else if (rc && framedur_ns) {
> >  		u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> >  
> > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> >  		      pipe, vblank->count, diff, cur_vblank, vblank->last);
> >  
> >  	if (diff == 0) {
> > -		WARN_ON_ONCE(cur_vblank != vblank->last);
> > +		WARN_ON_ONCE(max_vblank_count &&
> > +			     cur_vblank != vblank->last);
> 
> Unrelated bugfix for this warning? Should be a separate patch I think, or
> I'm missing something.

Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
does work until the exact point when we enable TV encoder. Thus we
will get non-zero values up to that point, and since the TV encoder
isn't yet throttling the pipe it presumably runs at the oversample
clock so our timestamp based estimates can give us a diff==0 even
though the pipe did indeed pass a vblank already. I forgot to
note this in the commit message.

I think we can handle this three ways:
1. do what I do here and just let the mismatch slip through
2. force i915_get_vblank_counter() to return 0 always when the
   TV encoder is going to be used
3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
   and instead delay it until just before we enable the TV encoder

I think option 3 is overly complicated to consider seriously. So
option 1 or option 2 is what I think we should do. For whatever
reason I went with option 1 here, but maybe option 2 is better
since it would be all contained within i915...

> 
> >  		return;
> >  	}
> >  
> > @@ -1204,6 +1213,28 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
> >  }
> >  EXPORT_SYMBOL(drm_crtc_vblank_reset);
> >  
> > +/**
> > + * drm_crtc_set_max_vblank_count - configure the hw max vblank counter value
> > + * @crtc: CRTC in question
> > + * @max_vblank_count: max hardware vblank counter value
> > + *
> > + * Update the maximum hardware vblank counter value for @crtc. Useful
> > + * for hardware where the operation of the hardware vblank counter
> > + * depends on the active display configuration.
> > + *
> > + * If used, must be called before drm_vblank_on().
> 
> I think we should check this at runtime with a WARN_ON. Plus make the
> comment here a bit clearer that this is indeed for runtime adjusting of
> the max_vblank_count, in cases where that depends upon the connected
> outputs.

Sure. I'll try to pimp up the docs a bit.

> 
> > + */
> > +void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
> > +				   u32 max_vblank_count)
> > +{
> > +	struct drm_device *dev = crtc->dev;
> > +	unsigned int pipe = drm_crtc_index(crtc);
> > +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > +
> > +	vblank->max_vblank_count = max_vblank_count;
> > +}
> > +EXPORT_SYMBOL(drm_crtc_set_max_vblank_count);
> > +
> >  /**
> >   * drm_crtc_vblank_on - enable vblank events on a CRTC
> >   * @crtc: CRTC in question
> > diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> > index 6ad9630d4f48..ecb2cf9913e2 100644
> > --- a/include/drm/drm_vblank.h
> > +++ b/include/drm/drm_vblank.h
> > @@ -128,6 +128,12 @@ struct drm_vblank_crtc {
> >  	 * @last: Protected by &drm_device.vbl_lock, used for wraparound handling.
> >  	 */
> >  	u32 last;
> > +	/**
> > +	 * @max_vblank_count: Maximum value of the hardware vblank counter.
> > +	 * If non-zero this takes precedence over &drm_device.max_vblank_count
> > +	 * for this crtc. Otherwise &drm_device.max_vblank_count is used.
> > +	 */
> 
> I'd add "This should be set by calling drm_crtc_set_max_vblank_count()."
> 
> And please also add a note to the kerneldoc of drm_driver.max_vblank_count
> pointing at &drm_vblank_crtc.max_vblank_count for per-crtc limits.

Ack.

> 
> Aside from the nits lgtm. I think I'll skip looking at the TV out stuff
> though ...

:)

Daniel Vetter Nov. 21, 2018, 3:19 p.m. UTC | #3

On Wed, Nov 21, 2018 at 01:37:51PM +0200, Ville Syrjälä wrote:
> On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> > On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > > From: Ville Syrjälä <[e-mail]>
> > > 
> > > On i965gm we need to adjust max_vblank_count dynamically
> > > depending on whether the TV encoder is used or not. To
> > > that end add a per-crtc max_vblank_count that takes
> > > precedence over its device wide counterpart. The driver
> > > can now call drm_crtc_set_max_vblank_count() to configure
> > > the per-crtc value before calling drm_vblank_on().
> > > 
> > > Also looks like there was some discussion about exynos needing
> > > similar treatment.
> > > 
> > > Cc: [e-mail]
> > > Cc: Inki Dae <[e-mail]>
> > > Cc: Daniel Vetter <[e-mail]>
> > > Signed-off-by: Ville Syrjälä <[e-mail]>
> > > ---
> > >  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> > >  include/drm/drm_vblank.h     |  8 ++++++++
> > >  2 files changed, 43 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > index 98e091175921..c3abbdca8aba 100644
> > > --- a/drivers/gpu/drm/drm_vblank.c
> > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> > >  	write_sequnlock(&vblank->seqlock);
> > >  }
> > >  
> > > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > > +{
> > > +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > +
> > > +	return vblank->max_vblank_count ?: dev->max_vblank_count;
> > > +}
> > > +
> > >  /*
> > >   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> > >   * if there is no useable hardware frame counter available.
> > >   */
> > >  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> > >  {
> > > -	WARN_ON_ONCE(dev->max_vblank_count != 0);
> > > +	WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> > >  	return 0;
> > >  }
> > >  
> > > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > >  	ktime_t t_vblank;
> > >  	int count = DRM_TIMESTAMP_MAXRETRIES;
> > >  	int framedur_ns = vblank->framedur_ns;
> > > +	u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> > >  
> > >  	/*
> > >  	 * Interrupts were disabled prior to this call, so deal with counter
> > > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > >  		rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> > >  	} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> > >  
> > > -	if (dev->max_vblank_count != 0) {
> > > +	if (max_vblank_count) {
> > >  		/* trust the hw counter when it's around */
> > > -		diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > > +		diff = (cur_vblank - vblank->last) & max_vblank_count;
> > >  	} else if (rc && framedur_ns) {
> > >  		u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> > >  
> > > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > >  		      pipe, vblank->count, diff, cur_vblank, vblank->last);
> > >  
> > >  	if (diff == 0) {
> > > -		WARN_ON_ONCE(cur_vblank != vblank->last);
> > > +		WARN_ON_ONCE(max_vblank_count &&
> > > +			     cur_vblank != vblank->last);
> > 
> > Unrelated bugfix for this warning? Should be a separate patch I think, or
> > I'm missing something.
> 
> Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
> does work until the exact point when we enable TV encoder. Thus we
> will get non-zero values up to that point, and since the TV encoder
> isn't yet throttling the pipe it presumably runs at the oversample
> clock so our timestamp based estimates can give us a diff==0 even
> though the pipe did indeed pass a vblank already. I forgot to
> note this in the commit message.
> 
> I think we can handle this three ways:
> 1. do what I do here and just let the mismatch slip through
> 2. force i915_get_vblank_counter() to return 0 always when the
>    TV encoder is going to be used
> 3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
>    and instead delay it until just before we enable the TV encoder
> 
> I think option 3 is overly complicated to consider seriously. So
> option 1 or option 2 is what I think we should do. For whatever
> reason I went with option 1 here, but maybe option 2 is better
> since it would be all contained within i915...

Delay drm_crtc_vblank_on until the vblank is stable? That seems like the
semantically clean solution to me, instead of hacking around in core code
when drivers leak garbage out ...

-Daniel


> > 
> > >  		return;
> > >  	}
> > >  
> > > @@ -1204,6 +1213,28 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
> > >  }
> > >  EXPORT_SYMBOL(drm_crtc_vblank_reset);
> > >  
> > > +/**
> > > + * drm_crtc_set_max_vblank_count - configure the hw max vblank counter value
> > > + * @crtc: CRTC in question
> > > + * @max_vblank_count: max hardware vblank counter value
> > > + *
> > > + * Update the maximum hardware vblank counter value for @crtc. Useful
> > > + * for hardware where the operation of the hardware vblank counter
> > > + * depends on the active display configuration.
> > > + *
> > > + * If used, must be called before drm_vblank_on().
> > 
> > I think we should check this at runtime with a WARN_ON. Plus make the
> > comment here a bit clearer that this is indeed for runtime adjusting of
> > the max_vblank_count, in cases where that depends upon the connected
> > outputs.
> 
> Sure. I'll try to pimp up the docs a bit.
> 
> > 
> > > + */
> > > +void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
> > > +				   u32 max_vblank_count)
> > > +{
> > > +	struct drm_device *dev = crtc->dev;
> > > +	unsigned int pipe = drm_crtc_index(crtc);
> > > +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > +
> > > +	vblank->max_vblank_count = max_vblank_count;
> > > +}
> > > +EXPORT_SYMBOL(drm_crtc_set_max_vblank_count);
> > > +
> > >  /**
> > >   * drm_crtc_vblank_on - enable vblank events on a CRTC
> > >   * @crtc: CRTC in question
> > > diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
> > > index 6ad9630d4f48..ecb2cf9913e2 100644
> > > --- a/include/drm/drm_vblank.h
> > > +++ b/include/drm/drm_vblank.h
> > > @@ -128,6 +128,12 @@ struct drm_vblank_crtc {
> > >  	 * @last: Protected by &drm_device.vbl_lock, used for wraparound handling.
> > >  	 */
> > >  	u32 last;
> > > +	/**
> > > +	 * @max_vblank_count: Maximum value of the hardware vblank counter.
> > > +	 * If non-zero this takes precedence over &drm_device.max_vblank_count
> > > +	 * for this crtc. Otherwise &drm_device.max_vblank_count is used.
> > > +	 */
> > 
> > I'd add "This should be set by calling drm_crtc_set_max_vblank_count()."
> > 
> > And please also add a note to the kerneldoc of drm_driver.max_vblank_count
> > pointing at &drm_vblank_crtc.max_vblank_count for per-crtc limits.
> 
> Ack.
> 
> > 
> > Aside from the nits lgtm. I think I'll skip looking at the TV out stuff
> > though ...
> 
> :)
> 
> -- 
> Ville Syrjälä
> Intel

Ville Syrjälä Nov. 21, 2018, 4:16 p.m. UTC | #4

On Wed, Nov 21, 2018 at 04:19:36PM +0100, Daniel Vetter wrote:
> On Wed, Nov 21, 2018 at 01:37:51PM +0200, Ville Syrjälä wrote:
> > On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> > > On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > > > From: Ville Syrjälä <[e-mail]>
> > > > 
> > > > On i965gm we need to adjust max_vblank_count dynamically
> > > > depending on whether the TV encoder is used or not. To
> > > > that end add a per-crtc max_vblank_count that takes
> > > > precedence over its device wide counterpart. The driver
> > > > can now call drm_crtc_set_max_vblank_count() to configure
> > > > the per-crtc value before calling drm_vblank_on().
> > > > 
> > > > Also looks like there was some discussion about exynos needing
> > > > similar treatment.
> > > > 
> > > > Cc: [e-mail]
> > > > Cc: Inki Dae <[e-mail]>
> > > > Cc: Daniel Vetter <[e-mail]>
> > > > Signed-off-by: Ville Syrjälä <[e-mail]>
> > > > ---
> > > >  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> > > >  include/drm/drm_vblank.h     |  8 ++++++++
> > > >  2 files changed, 43 insertions(+), 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > > index 98e091175921..c3abbdca8aba 100644
> > > > --- a/drivers/gpu/drm/drm_vblank.c
> > > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> > > >  	write_sequnlock(&vblank->seqlock);
> > > >  }
> > > >  
> > > > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > > > +{
> > > > +	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > > +
> > > > +	return vblank->max_vblank_count ?: dev->max_vblank_count;
> > > > +}
> > > > +
> > > >  /*
> > > >   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> > > >   * if there is no useable hardware frame counter available.
> > > >   */
> > > >  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> > > >  {
> > > > -	WARN_ON_ONCE(dev->max_vblank_count != 0);
> > > > +	WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> > > >  	return 0;
> > > >  }
> > > >  
> > > > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > >  	ktime_t t_vblank;
> > > >  	int count = DRM_TIMESTAMP_MAXRETRIES;
> > > >  	int framedur_ns = vblank->framedur_ns;
> > > > +	u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> > > >  
> > > >  	/*
> > > >  	 * Interrupts were disabled prior to this call, so deal with counter
> > > > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > >  		rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> > > >  	} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> > > >  
> > > > -	if (dev->max_vblank_count != 0) {
> > > > +	if (max_vblank_count) {
> > > >  		/* trust the hw counter when it's around */
> > > > -		diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > > > +		diff = (cur_vblank - vblank->last) & max_vblank_count;
> > > >  	} else if (rc && framedur_ns) {
> > > >  		u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> > > >  
> > > > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > >  		      pipe, vblank->count, diff, cur_vblank, vblank->last);
> > > >  
> > > >  	if (diff == 0) {
> > > > -		WARN_ON_ONCE(cur_vblank != vblank->last);
> > > > +		WARN_ON_ONCE(max_vblank_count &&
> > > > +			     cur_vblank != vblank->last);
> > > 
> > > Unrelated bugfix for this warning? Should be a separate patch I think, or
> > > I'm missing something.
> > 
> > Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
> > does work until the exact point when we enable TV encoder. Thus we
> > will get non-zero values up to that point, and since the TV encoder
> > isn't yet throttling the pipe it presumably runs at the oversample
> > clock so our timestamp based estimates can give us a diff==0 even
> > though the pipe did indeed pass a vblank already. I forgot to
> > note this in the commit message.
> > 
> > I think we can handle this three ways:
> > 1. do what I do here and just let the mismatch slip through
> > 2. force i915_get_vblank_counter() to return 0 always when the
> >    TV encoder is going to be used
> > 3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
> >    and instead delay it until just before we enable the TV encoder
> > 
> > I think option 3 is overly complicated to consider seriously. So
> > option 1 or option 2 is what I think we should do. For whatever
> > reason I went with option 1 here, but maybe option 2 is better
> > since it would be all contained within i915...
> 
> Delay drm_crtc_vblank_on until the vblank is stable? That seems like the
> semantically clean solution to me, instead of hacking around in core code
> when drivers leak garbage out ...

We need a vblank wait before turning on the TV encoder. Chicken vs. egg.

Daniel Vetter Nov. 21, 2018, 4:22 p.m. UTC | #5

On Wed, Nov 21, 2018 at 5:16 PM Ville Syrjälä
<[e-mail]> wrote:
>
> On Wed, Nov 21, 2018 at 04:19:36PM +0100, Daniel Vetter wrote:
> > On Wed, Nov 21, 2018 at 01:37:51PM +0200, Ville Syrjälä wrote:
> > > On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> > > > On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > > > > From: Ville Syrjälä <[e-mail]>
> > > > >
> > > > > On i965gm we need to adjust max_vblank_count dynamically
> > > > > depending on whether the TV encoder is used or not. To
> > > > > that end add a per-crtc max_vblank_count that takes
> > > > > precedence over its device wide counterpart. The driver
> > > > > can now call drm_crtc_set_max_vblank_count() to configure
> > > > > the per-crtc value before calling drm_vblank_on().
> > > > >
> > > > > Also looks like there was some discussion about exynos needing
> > > > > similar treatment.
> > > > >
> > > > > Cc: [e-mail]
> > > > > Cc: Inki Dae <[e-mail]>
> > > > > Cc: Daniel Vetter <[e-mail]>
> > > > > Signed-off-by: Ville Syrjälä <[e-mail]>
> > > > > ---
> > > > >  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> > > > >  include/drm/drm_vblank.h     |  8 ++++++++
> > > > >  2 files changed, 43 insertions(+), 4 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > > > index 98e091175921..c3abbdca8aba 100644
> > > > > --- a/drivers/gpu/drm/drm_vblank.c
> > > > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > > > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> > > > >         write_sequnlock(&vblank->seqlock);
> > > > >  }
> > > > >
> > > > > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > > > > +{
> > > > > +       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > > > +
> > > > > +       return vblank->max_vblank_count ?: dev->max_vblank_count;
> > > > > +}
> > > > > +
> > > > >  /*
> > > > >   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> > > > >   * if there is no useable hardware frame counter available.
> > > > >   */
> > > > >  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> > > > >  {
> > > > > -       WARN_ON_ONCE(dev->max_vblank_count != 0);
> > > > > +       WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> > > > >         return 0;
> > > > >  }
> > > > >
> > > > > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > >         ktime_t t_vblank;
> > > > >         int count = DRM_TIMESTAMP_MAXRETRIES;
> > > > >         int framedur_ns = vblank->framedur_ns;
> > > > > +       u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> > > > >
> > > > >         /*
> > > > >          * Interrupts were disabled prior to this call, so deal with counter
> > > > > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > >                 rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> > > > >         } while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> > > > >
> > > > > -       if (dev->max_vblank_count != 0) {
> > > > > +       if (max_vblank_count) {
> > > > >                 /* trust the hw counter when it's around */
> > > > > -               diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > > > > +               diff = (cur_vblank - vblank->last) & max_vblank_count;
> > > > >         } else if (rc && framedur_ns) {
> > > > >                 u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> > > > >
> > > > > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > >                       pipe, vblank->count, diff, cur_vblank, vblank->last);
> > > > >
> > > > >         if (diff == 0) {
> > > > > -               WARN_ON_ONCE(cur_vblank != vblank->last);
> > > > > +               WARN_ON_ONCE(max_vblank_count &&
> > > > > +                            cur_vblank != vblank->last);
> > > >
> > > > Unrelated bugfix for this warning? Should be a separate patch I think, or
> > > > I'm missing something.
> > >
> > > Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
> > > does work until the exact point when we enable TV encoder. Thus we
> > > will get non-zero values up to that point, and since the TV encoder
> > > isn't yet throttling the pipe it presumably runs at the oversample
> > > clock so our timestamp based estimates can give us a diff==0 even
> > > though the pipe did indeed pass a vblank already. I forgot to
> > > note this in the commit message.
> > >
> > > I think we can handle this three ways:
> > > 1. do what I do here and just let the mismatch slip through
> > > 2. force i915_get_vblank_counter() to return 0 always when the
> > >    TV encoder is going to be used
> > > 3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
> > >    and instead delay it until just before we enable the TV encoder
> > >
> > > I think option 3 is overly complicated to consider seriously. So
> > > option 1 or option 2 is what I think we should do. For whatever
> > > reason I went with option 1 here, but maybe option 2 is better
> > > since it would be all contained within i915...
> >
> > Delay drm_crtc_vblank_on until the vblank is stable? That seems like the
> > semantically clean solution to me, instead of hacking around in core code
> > when drivers leak garbage out ...
>
> We need a vblank wait before turning on the TV encoder. Chicken vs. egg.

Gah.

Ok I think I think having the hack here makes sense then, but split
out as a separate patch with separate justification. It's a bit a
tricky thing that deserves to be higlighted (and easier way to found
the explanation with git blame in case it's ever needed).
-Daniel

Ville Syrjälä Nov. 21, 2018, 4:46 p.m. UTC | #6

On Wed, Nov 21, 2018 at 05:22:49PM +0100, Daniel Vetter wrote:
> On Wed, Nov 21, 2018 at 5:16 PM Ville Syrjälä
> <[e-mail]> wrote:
> >
> > On Wed, Nov 21, 2018 at 04:19:36PM +0100, Daniel Vetter wrote:
> > > On Wed, Nov 21, 2018 at 01:37:51PM +0200, Ville Syrjälä wrote:
> > > > On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> > > > > On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > > > > > From: Ville Syrjälä <[e-mail]>
> > > > > >
> > > > > > On i965gm we need to adjust max_vblank_count dynamically
> > > > > > depending on whether the TV encoder is used or not. To
> > > > > > that end add a per-crtc max_vblank_count that takes
> > > > > > precedence over its device wide counterpart. The driver
> > > > > > can now call drm_crtc_set_max_vblank_count() to configure
> > > > > > the per-crtc value before calling drm_vblank_on().
> > > > > >
> > > > > > Also looks like there was some discussion about exynos needing
> > > > > > similar treatment.
> > > > > >
> > > > > > Cc: [e-mail]
> > > > > > Cc: Inki Dae <[e-mail]>
> > > > > > Cc: Daniel Vetter <[e-mail]>
> > > > > > Signed-off-by: Ville Syrjälä <[e-mail]>
> > > > > > ---
> > > > > >  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> > > > > >  include/drm/drm_vblank.h     |  8 ++++++++
> > > > > >  2 files changed, 43 insertions(+), 4 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > > > > index 98e091175921..c3abbdca8aba 100644
> > > > > > --- a/drivers/gpu/drm/drm_vblank.c
> > > > > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > > > > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> > > > > >         write_sequnlock(&vblank->seqlock);
> > > > > >  }
> > > > > >
> > > > > > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > > > > > +{
> > > > > > +       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > > > > +
> > > > > > +       return vblank->max_vblank_count ?: dev->max_vblank_count;
> > > > > > +}
> > > > > > +
> > > > > >  /*
> > > > > >   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> > > > > >   * if there is no useable hardware frame counter available.
> > > > > >   */
> > > > > >  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> > > > > >  {
> > > > > > -       WARN_ON_ONCE(dev->max_vblank_count != 0);
> > > > > > +       WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> > > > > >         return 0;
> > > > > >  }
> > > > > >
> > > > > > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > >         ktime_t t_vblank;
> > > > > >         int count = DRM_TIMESTAMP_MAXRETRIES;
> > > > > >         int framedur_ns = vblank->framedur_ns;
> > > > > > +       u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> > > > > >
> > > > > >         /*
> > > > > >          * Interrupts were disabled prior to this call, so deal with counter
> > > > > > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > >                 rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> > > > > >         } while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> > > > > >
> > > > > > -       if (dev->max_vblank_count != 0) {
> > > > > > +       if (max_vblank_count) {
> > > > > >                 /* trust the hw counter when it's around */
> > > > > > -               diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > > > > > +               diff = (cur_vblank - vblank->last) & max_vblank_count;
> > > > > >         } else if (rc && framedur_ns) {
> > > > > >                 u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> > > > > >
> > > > > > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > >                       pipe, vblank->count, diff, cur_vblank, vblank->last);
> > > > > >
> > > > > >         if (diff == 0) {
> > > > > > -               WARN_ON_ONCE(cur_vblank != vblank->last);
> > > > > > +               WARN_ON_ONCE(max_vblank_count &&
> > > > > > +                            cur_vblank != vblank->last);
> > > > >
> > > > > Unrelated bugfix for this warning? Should be a separate patch I think, or
> > > > > I'm missing something.
> > > >
> > > > Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
> > > > does work until the exact point when we enable TV encoder. Thus we
> > > > will get non-zero values up to that point, and since the TV encoder
> > > > isn't yet throttling the pipe it presumably runs at the oversample
> > > > clock so our timestamp based estimates can give us a diff==0 even
> > > > though the pipe did indeed pass a vblank already. I forgot to
> > > > note this in the commit message.
> > > >
> > > > I think we can handle this three ways:
> > > > 1. do what I do here and just let the mismatch slip through
> > > > 2. force i915_get_vblank_counter() to return 0 always when the
> > > >    TV encoder is going to be used
> > > > 3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
> > > >    and instead delay it until just before we enable the TV encoder
> > > >
> > > > I think option 3 is overly complicated to consider seriously. So
> > > > option 1 or option 2 is what I think we should do. For whatever
> > > > reason I went with option 1 here, but maybe option 2 is better
> > > > since it would be all contained within i915...
> > >
> > > Delay drm_crtc_vblank_on until the vblank is stable? That seems like the
> > > semantically clean solution to me, instead of hacking around in core code
> > > when drivers leak garbage out ...
> >
> > We need a vblank wait before turning on the TV encoder. Chicken vs. egg.
> 
> Gah.
> 
> Ok I think I think having the hack here makes sense then, but split
> out as a separate patch with separate justification. It's a bit a
> tricky thing that deserves to be higlighted (and easier way to found
> the explanation with git blame in case it's ever needed).

Or we go with option 2. It doesn't seem too bad actually.

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 019cb685986c..26d86aedc7ac 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -822,11 +822,26 @@ static void i915_enable_asle_pipestat(struct drm_i915_private *dev_priv)
 static u32 i915_get_vblank_counter(struct drm_device *dev, unsigned int pipe)
 {
        struct drm_i915_private *dev_priv = to_i915(dev);
+       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+       const struct drm_display_mode *mode = vblank->hwmode;
        i915_reg_t high_frame, low_frame;
        u32 high1, high2, low, pixel, vbl_start, hsync_start, htotal;
-       const struct drm_display_mode *mode = &dev->vblank[pipe].hwmode;
        unsigned long irqflags;
 
+       /*
+        * On i965gm TV output the frame counter works up to
+        * the point when we enable the TV encoder. After that the
+        * frame counter ceases to work and reads zero. We need a
+        * vblank wait before enabling the TV encoder and so we
+        * have to enable vblank interrupts while the frame counter
+        * is still in a working state. However the core vblank code
+        * does not like us returning non-zero frame counter values
+        * when we've told it that we don't have a working frame
+        * counter. Thus we must stop non-zero values leaking out.
+        */
+       if (!vblank->max_vblank_count)
+               return 0;
+
        htotal = mode->crtc_htotal;
        hsync_start = mode->crtc_hsync_start;
        vbl_start = mode->crtc_vblank_start;

Daniel Vetter Nov. 22, 2018, 8:53 a.m. UTC | #7

On Wed, Nov 21, 2018 at 06:46:57PM +0200, Ville Syrjälä wrote:
> On Wed, Nov 21, 2018 at 05:22:49PM +0100, Daniel Vetter wrote:
> > On Wed, Nov 21, 2018 at 5:16 PM Ville Syrjälä
> > <[e-mail]> wrote:
> > >
> > > On Wed, Nov 21, 2018 at 04:19:36PM +0100, Daniel Vetter wrote:
> > > > On Wed, Nov 21, 2018 at 01:37:51PM +0200, Ville Syrjälä wrote:
> > > > > On Wed, Nov 21, 2018 at 10:27:27AM +0100, Daniel Vetter wrote:
> > > > > > On Mon, Nov 12, 2018 at 06:59:45PM +0200, Ville Syrjala wrote:
> > > > > > > From: Ville Syrjälä <[e-mail]>
> > > > > > >
> > > > > > > On i965gm we need to adjust max_vblank_count dynamically
> > > > > > > depending on whether the TV encoder is used or not. To
> > > > > > > that end add a per-crtc max_vblank_count that takes
> > > > > > > precedence over its device wide counterpart. The driver
> > > > > > > can now call drm_crtc_set_max_vblank_count() to configure
> > > > > > > the per-crtc value before calling drm_vblank_on().
> > > > > > >
> > > > > > > Also looks like there was some discussion about exynos needing
> > > > > > > similar treatment.
> > > > > > >
> > > > > > > Cc: [e-mail]
> > > > > > > Cc: Inki Dae <[e-mail]>
> > > > > > > Cc: Daniel Vetter <[e-mail]>
> > > > > > > Signed-off-by: Ville Syrjälä <[e-mail]>
> > > > > > > ---
> > > > > > >  drivers/gpu/drm/drm_vblank.c | 39 ++++++++++++++++++++++++++++++++----
> > > > > > >  include/drm/drm_vblank.h     |  8 ++++++++
> > > > > > >  2 files changed, 43 insertions(+), 4 deletions(-)
> > > > > > >
> > > > > > > diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
> > > > > > > index 98e091175921..c3abbdca8aba 100644
> > > > > > > --- a/drivers/gpu/drm/drm_vblank.c
> > > > > > > +++ b/drivers/gpu/drm/drm_vblank.c
> > > > > > > @@ -105,13 +105,20 @@ static void store_vblank(struct drm_device *dev, unsigned int pipe,
> > > > > > >         write_sequnlock(&vblank->seqlock);
> > > > > > >  }
> > > > > > >
> > > > > > > +static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
> > > > > > > +{
> > > > > > > +       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> > > > > > > +
> > > > > > > +       return vblank->max_vblank_count ?: dev->max_vblank_count;
> > > > > > > +}
> > > > > > > +
> > > > > > >  /*
> > > > > > >   * "No hw counter" fallback implementation of .get_vblank_counter() hook,
> > > > > > >   * if there is no useable hardware frame counter available.
> > > > > > >   */
> > > > > > >  static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
> > > > > > >  {
> > > > > > > -       WARN_ON_ONCE(dev->max_vblank_count != 0);
> > > > > > > +       WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
> > > > > > >         return 0;
> > > > > > >  }
> > > > > > >
> > > > > > > @@ -198,6 +205,7 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > > >         ktime_t t_vblank;
> > > > > > >         int count = DRM_TIMESTAMP_MAXRETRIES;
> > > > > > >         int framedur_ns = vblank->framedur_ns;
> > > > > > > +       u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
> > > > > > >
> > > > > > >         /*
> > > > > > >          * Interrupts were disabled prior to this call, so deal with counter
> > > > > > > @@ -216,9 +224,9 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > > >                 rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
> > > > > > >         } while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
> > > > > > >
> > > > > > > -       if (dev->max_vblank_count != 0) {
> > > > > > > +       if (max_vblank_count) {
> > > > > > >                 /* trust the hw counter when it's around */
> > > > > > > -               diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
> > > > > > > +               diff = (cur_vblank - vblank->last) & max_vblank_count;
> > > > > > >         } else if (rc && framedur_ns) {
> > > > > > >                 u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
> > > > > > >
> > > > > > > @@ -258,7 +266,8 @@ static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
> > > > > > >                       pipe, vblank->count, diff, cur_vblank, vblank->last);
> > > > > > >
> > > > > > >         if (diff == 0) {
> > > > > > > -               WARN_ON_ONCE(cur_vblank != vblank->last);
> > > > > > > +               WARN_ON_ONCE(max_vblank_count &&
> > > > > > > +                            cur_vblank != vblank->last);
> > > > > >
> > > > > > Unrelated bugfix for this warning? Should be a separate patch I think, or
> > > > > > I'm missing something.
> > > > >
> > > > > Ah, yeah this was due to a quirk of i965gm hardware. The hw counter
> > > > > does work until the exact point when we enable TV encoder. Thus we
> > > > > will get non-zero values up to that point, and since the TV encoder
> > > > > isn't yet throttling the pipe it presumably runs at the oversample
> > > > > clock so our timestamp based estimates can give us a diff==0 even
> > > > > though the pipe did indeed pass a vblank already. I forgot to
> > > > > note this in the commit message.
> > > > >
> > > > > I think we can handle this three ways:
> > > > > 1. do what I do here and just let the mismatch slip through
> > > > > 2. force i915_get_vblank_counter() to return 0 always when the
> > > > >    TV encoder is going to be used
> > > > > 3. don't call drm_crtc_set_max_vblank_count() before drm_vblank_on()
> > > > >    and instead delay it until just before we enable the TV encoder
> > > > >
> > > > > I think option 3 is overly complicated to consider seriously. So
> > > > > option 1 or option 2 is what I think we should do. For whatever
> > > > > reason I went with option 1 here, but maybe option 2 is better
> > > > > since it would be all contained within i915...
> > > >
> > > > Delay drm_crtc_vblank_on until the vblank is stable? That seems like the
> > > > semantically clean solution to me, instead of hacking around in core code
> > > > when drivers leak garbage out ...
> > >
> > > We need a vblank wait before turning on the TV encoder. Chicken vs. egg.
> > 
> > Gah.
> > 
> > Ok I think I think having the hack here makes sense then, but split
> > out as a separate patch with separate justification. It's a bit a
> > tricky thing that deserves to be higlighted (and easier way to found
> > the explanation with git blame in case it's ever needed).
> 
> Or we go with option 2. It doesn't seem too bad actually.
> 
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 019cb685986c..26d86aedc7ac 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -822,11 +822,26 @@ static void i915_enable_asle_pipestat(struct drm_i915_private *dev_priv)
>  static u32 i915_get_vblank_counter(struct drm_device *dev, unsigned int pipe)
>  {
>         struct drm_i915_private *dev_priv = to_i915(dev);
> +       struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
> +       const struct drm_display_mode *mode = vblank->hwmode;
>         i915_reg_t high_frame, low_frame;
>         u32 high1, high2, low, pixel, vbl_start, hsync_start, htotal;
> -       const struct drm_display_mode *mode = &dev->vblank[pipe].hwmode;
>         unsigned long irqflags;
>  
> +       /*
> +        * On i965gm TV output the frame counter works up to
> +        * the point when we enable the TV encoder. After that the
> +        * frame counter ceases to work and reads zero. We need a
> +        * vblank wait before enabling the TV encoder and so we
> +        * have to enable vblank interrupts while the frame counter
> +        * is still in a working state. However the core vblank code
> +        * does not like us returning non-zero frame counter values
> +        * when we've told it that we don't have a working frame
> +        * counter. Thus we must stop non-zero values leaking out.
> +        */
> +       if (!vblank->max_vblank_count)
> +               return 0;

Hm yeah, looks reasonable actually. And less hacks in the shared code.
-Daniel

> +
>         htotal = mode->crtc_htotal;
>         hsync_start = mode->crtc_hsync_start;
>         vbl_start = mode->crtc_vblank_start;
> 
> -- 
> Ville Syrjälä
> Intel

Patch

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 98e091175921..c3abbdca8aba 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -105,13 +105,20 @@  static void store_vblank(struct drm_device *dev, unsigned int pipe,
 	write_sequnlock(&vblank->seqlock);
 }
 
+static u32 drm_max_vblank_count(struct drm_device *dev, unsigned int pipe)
+{
+	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+	return vblank->max_vblank_count ?: dev->max_vblank_count;
+}
+
 /*
  * "No hw counter" fallback implementation of .get_vblank_counter() hook,
  * if there is no useable hardware frame counter available.
  */
 static u32 drm_vblank_no_hw_counter(struct drm_device *dev, unsigned int pipe)
 {
-	WARN_ON_ONCE(dev->max_vblank_count != 0);
+	WARN_ON_ONCE(drm_max_vblank_count(dev, pipe) != 0);
 	return 0;
 }
 
@@ -198,6 +205,7 @@  static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
 	ktime_t t_vblank;
 	int count = DRM_TIMESTAMP_MAXRETRIES;
 	int framedur_ns = vblank->framedur_ns;
+	u32 max_vblank_count = drm_max_vblank_count(dev, pipe);
 
 	/*
 	 * Interrupts were disabled prior to this call, so deal with counter
@@ -216,9 +224,9 @@  static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
 		rc = drm_get_last_vbltimestamp(dev, pipe, &t_vblank, in_vblank_irq);
 	} while (cur_vblank != __get_vblank_counter(dev, pipe) && --count > 0);
 
-	if (dev->max_vblank_count != 0) {
+	if (max_vblank_count) {
 		/* trust the hw counter when it's around */
-		diff = (cur_vblank - vblank->last) & dev->max_vblank_count;
+		diff = (cur_vblank - vblank->last) & max_vblank_count;
 	} else if (rc && framedur_ns) {
 		u64 diff_ns = ktime_to_ns(ktime_sub(t_vblank, vblank->time));
 
@@ -258,7 +266,8 @@  static void drm_update_vblank_count(struct drm_device *dev, unsigned int pipe,
 		      pipe, vblank->count, diff, cur_vblank, vblank->last);
 
 	if (diff == 0) {
-		WARN_ON_ONCE(cur_vblank != vblank->last);
+		WARN_ON_ONCE(max_vblank_count &&
+			     cur_vblank != vblank->last);
 		return;
 	}
 
@@ -1204,6 +1213,28 @@  void drm_crtc_vblank_reset(struct drm_crtc *crtc)
 }
 EXPORT_SYMBOL(drm_crtc_vblank_reset);
 
+/**
+ * drm_crtc_set_max_vblank_count - configure the hw max vblank counter value
+ * @crtc: CRTC in question
+ * @max_vblank_count: max hardware vblank counter value
+ *
+ * Update the maximum hardware vblank counter value for @crtc. Useful
+ * for hardware where the operation of the hardware vblank counter
+ * depends on the active display configuration.
+ *
+ * If used, must be called before drm_vblank_on().
+ */
+void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
+				   u32 max_vblank_count)
+{
+	struct drm_device *dev = crtc->dev;
+	unsigned int pipe = drm_crtc_index(crtc);
+	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+
+	vblank->max_vblank_count = max_vblank_count;
+}
+EXPORT_SYMBOL(drm_crtc_set_max_vblank_count);
+
 /**
  * drm_crtc_vblank_on - enable vblank events on a CRTC
  * @crtc: CRTC in question
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 6ad9630d4f48..ecb2cf9913e2 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -128,6 +128,12 @@  struct drm_vblank_crtc {
 	 * @last: Protected by &drm_device.vbl_lock, used for wraparound handling.
 	 */
 	u32 last;
+	/**
+	 * @max_vblank_count: Maximum value of the hardware vblank counter.
+	 * If non-zero this takes precedence over &drm_device.max_vblank_count
+	 * for this crtc. Otherwise &drm_device.max_vblank_count is used.
+	 */
+	u32 max_vblank_count;
 	/**
 	 * @inmodeset: Tracks whether the vblank is disabled due to a modeset.
 	 * For legacy driver bit 2 additionally tracks whether an additional
@@ -206,4 +212,6 @@  bool drm_calc_vbltimestamp_from_scanoutpos(struct drm_device *dev,
 void drm_calc_timestamping_constants(struct drm_crtc *crtc,
 				     const struct drm_display_mode *mode);
 wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
+void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
+				   u32 max_vblank_count);
 #endif