Re: [Intel-gfx] [PATCH 2/3] drm/i915: Do vblank evasion correctly if vrr push has already been sent

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

On Wed, Nov 17, 2021 at 01:10:13PM -0800, Navare, Manasi wrote:
> On Wed, Nov 17, 2021 at 08:31:02PM +0200, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > 
> > Let's adjust the vblank evasion to account for the case where
> > a push has already been sent. In that case the vblank exit will start
> > at vmin vblank start (as opposed to vmax vblank start when no push
> > has been sent).
> > 
> > This should minimize the effects of the tiny race between sampling
> > the frame counter vs. intel_vrr_send_push() during the previous frame.
> > This will also be required if we want to do mailbox style updates with
> > vrr since then we'd definitely do multiple commits per frame. Currently
> > mailbox updates are only used by the legacy cursor, but we don't do
> > vrr push for those.
> > 
> > Cc: Manasi Navare <manasi.d.navare@intel.com>
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_crtc.c | 10 +++++++---
> >  drivers/gpu/drm/i915/display/intel_vrr.c  | 12 ++++++++++++
> >  drivers/gpu/drm/i915/display/intel_vrr.h  |  1 +
> >  3 files changed, 20 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_crtc.c b/drivers/gpu/drm/i915/display/intel_crtc.c
> > index cf403be7736c..eb5444f90e77 100644
> > --- a/drivers/gpu/drm/i915/display/intel_crtc.c
> > +++ b/drivers/gpu/drm/i915/display/intel_crtc.c
> > @@ -470,10 +470,14 @@ void intel_pipe_update_start(struct intel_crtc_state *new_crtc_state)
> >  	if (intel_crtc_needs_vblank_work(new_crtc_state))
> >  		intel_crtc_vblank_work_init(new_crtc_state);
> >  
> > -	if (new_crtc_state->vrr.enable)
> > -		vblank_start = intel_vrr_vmax_vblank_start(new_crtc_state);
> > -	else
> > +	if (new_crtc_state->vrr.enable) {
> > +		if (intel_vrr_is_push_sent(new_crtc_state))
> > +			vblank_start = intel_vrr_vmin_vblank_start(new_crtc_state);
> 
> Actually if Push is sent then the vblank gets terminated at that point which falls between vmin and vmax so
> not necessarily at Vmin but at anytime between vmin and vmax. Is it correct to calculate it based on vmin?

If you do a push between vmin and vmax then the vblank terminates
immediately and the PUSH_SEND bit gets cleared. The only way the bit
stays set is you set it after vmax/before vmin.

> 
> > +		else
> > +			vblank_start = intel_vrr_vmax_vblank_start(new_crtc_state);
> > +	} else {
> >  		vblank_start = intel_mode_vblank_start(adjusted_mode);
> > +	}
> >  
> >  	/* FIXME needs to be calibrated sensibly */
> >  	min = vblank_start - intel_usecs_to_scanlines(adjusted_mode,
> > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> > index c335b1dbafcf..db1c3902fc2d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> > +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> > @@ -193,6 +193,18 @@ void intel_vrr_send_push(const struct intel_crtc_state *crtc_state)
> >  		       TRANS_PUSH_EN | TRANS_PUSH_SEND);
> >  }
> >  
> > +bool intel_vrr_is_push_sent(const struct intel_crtc_state *crtc_state)
> > +{
> > +	struct intel_crtc *crtc = to_intel_crtc(crtc_state->uapi.crtc);
> > +	struct drm_i915_private *dev_priv = to_i915(crtc->base.dev);
> > +	enum transcoder cpu_transcoder = crtc_state->cpu_transcoder;
> > +
> > +	if (!crtc_state->vrr.enable)
> > +		return false;
> > +
> > +	return intel_de_read(dev_priv, TRANS_PUSH(cpu_transcoder)) & TRANS_PUSH_SEND;
> 
> But HW clears this bit after double buffer update. Is this a good inidcation to check the PUSH_SEND bit?
> 
> Manasi
> 
> > +}
> > +
> >  void intel_vrr_disable(const struct intel_crtc_state *old_crtc_state)
> >  {
> >  	struct intel_crtc *crtc = to_intel_crtc(old_crtc_state->uapi.crtc);
> > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.h b/drivers/gpu/drm/i915/display/intel_vrr.h
> > index 96f9c9c27ab9..1c2da572693d 100644
> > --- a/drivers/gpu/drm/i915/display/intel_vrr.h
> > +++ b/drivers/gpu/drm/i915/display/intel_vrr.h
> > @@ -23,6 +23,7 @@ void intel_vrr_compute_config(struct intel_crtc_state *crtc_state,
> >  void intel_vrr_enable(struct intel_encoder *encoder,
> >  		      const struct intel_crtc_state *crtc_state);
> >  void intel_vrr_send_push(const struct intel_crtc_state *crtc_state);
> > +bool intel_vrr_is_push_sent(const struct intel_crtc_state *crtc_state);
> >  void intel_vrr_disable(const struct intel_crtc_state *old_crtc_state);
> >  void intel_vrr_get_config(struct intel_crtc *crtc,
> >  			  struct intel_crtc_state *crtc_state);
> > -- 
> > 2.32.0
> > 

-- 
Ville Syrjälä
Intel