Re: [PATCH 04/19] drm/i915: Add support for detecting vblanks when hw frame counter is unavailable.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Wed, Apr 27, 2016 at 04:06:16PM +0200, Patrik Jakobsson wrote:
> On Tue, Apr 19, 2016 at 09:52:24AM +0200, Maarten Lankhorst wrote:
> > This uses the newly created drm_accurate_vblank_count_and_time to accurately
> > get a vblank count when the hw counter is unavailable.
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 10 ++++++++++
> >  drivers/gpu/drm/i915/intel_drv.h     |  3 +++
> >  drivers/gpu/drm/i915/intel_sprite.c  |  8 ++------
> >  3 files changed, 15 insertions(+), 6 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index ccbc2a448258..2086e8bd10da 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -13530,6 +13530,16 @@ static int intel_atomic_prepare_commit(struct drm_device *dev,
> >  	return ret;
> >  }
> >  
> > +u32 intel_crtc_get_vblank_counter(struct intel_crtc *crtc)
> > +{
> > +	struct drm_device *dev = crtc->base.dev;
> > +
> > +	if (!dev->max_vblank_count)
> > +		return drm_accurate_vblank_count(&crtc->base);
> > +
> > +	return dev->driver->get_vblank_counter(dev, crtc->pipe);
> > +}
> > +
> >  static void intel_atomic_wait_for_vblanks(struct drm_device *dev,
> >  					  struct drm_i915_private *dev_priv,
> >  					  unsigned crtc_mask)
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index fecc89600667..8efeb90eac07 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -1146,6 +1146,9 @@ intel_wait_for_vblank_if_active(struct drm_device *dev, int pipe)
> >  	if (crtc->active)
> >  		intel_wait_for_vblank(dev, pipe);
> >  }
> > +
> > +u32 intel_crtc_get_vblank_counter(struct intel_crtc *crtc);
> > +
> >  int ironlake_get_lanes_required(int target_clock, int link_bw, int bpp);
> >  void vlv_wait_port_ready(struct drm_i915_private *dev_priv,
> >  			 struct intel_digital_port *dport,
> > diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
> > index 0f3e2303e0e9..e2de6b0df5a8 100644
> > --- a/drivers/gpu/drm/i915/intel_sprite.c
> > +++ b/drivers/gpu/drm/i915/intel_sprite.c
> > @@ -80,9 +80,7 @@ static int usecs_to_scanlines(const struct drm_display_mode *adjusted_mode,
> >   */
> >  void intel_pipe_update_start(struct intel_crtc *crtc)
> >  {
> > -	struct drm_device *dev = crtc->base.dev;
> >  	const struct drm_display_mode *adjusted_mode = &crtc->config->base.adjusted_mode;
> > -	enum pipe pipe = crtc->pipe;
> >  	long timeout = msecs_to_jiffies_timeout(1);
> >  	int scanline, min, max, vblank_start;
> >  	wait_queue_head_t *wq = drm_crtc_vblank_waitqueue(&crtc->base);
> > @@ -139,8 +137,7 @@ void intel_pipe_update_start(struct intel_crtc *crtc)
> >  
> >  	crtc->debug.scanline_start = scanline;
> >  	crtc->debug.start_vbl_time = ktime_get();
> > -	crtc->debug.start_vbl_count =
> > -		dev->driver->get_vblank_counter(dev, pipe);
> > +	crtc->debug.start_vbl_count = intel_crtc_get_vblank_counter(crtc);
> >  
> >  	trace_i915_pipe_update_vblank_evaded(crtc);
> >  }
> > @@ -156,10 +153,9 @@ void intel_pipe_update_start(struct intel_crtc *crtc)
> >   */
> >  void intel_pipe_update_end(struct intel_crtc *crtc)
> >  {
> > -	struct drm_device *dev = crtc->base.dev;
> >  	enum pipe pipe = crtc->pipe;
> >  	int scanline_end = intel_get_crtc_scanline(crtc);
> > -	u32 end_vbl_count = dev->driver->get_vblank_counter(dev, pipe);
> > +	u32 end_vbl_count = intel_crtc_get_vblank_counter(crtc);
> >  	ktime_t end_vbl_time = ktime_get();
> >  
> >  	trace_i915_pipe_update_end(crtc, end_vbl_count, scanline_end);
> 
> Do we need to use intel_crtc_get_vblank_counter() in
> display_pipe_crc_irq_handler() as well?

There was a bit of talk whether we should use hw or sw counter for the
crc frame numbers, but I can't remember if we reached any real
conclusion. In the meantime the crc frame counters are all still zero
on gen2, meaning the tests don't work all that well. See [1].

And we still have the %8d bug highlited in that same patch series. Not
sure we reached any conclusion about that on either.

In any case using drm_accurate_vblank_count() from the irq handler
would be somewhat silly since the irq handler should have just updated
the sw counter to be uptodate, assuming we had vblank irqs enabled.

[1] https://lists.freedesktop.org/archives/intel-gfx/2015-December/083035.html

-- 
Ville Syrjälä
Intel OTC
_______________________________________________
Intel-gfx mailing list
Intel-gfx@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/intel-gfx