Re: [PATCH 5/5] drm/i915/vrr: Move the TGL SCL manging of vmin/vmax/flipline deeper

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

On Thu, Sep 18, 2025 at 03:03:02PM +0530, Nautiyal, Ankit K wrote:
> 
> On 9/18/2025 2:04 AM, Ville Syrjala wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Currently our crtc_state->vrr.{vmin.vmax,flipline} are mangled on
> > TGL to account for the SCL delay (the hardware requires this mangling
> > or the actual vtotals will become incorrect).
> 
> Please correct me if I am wrong:
> 
> For display < 13  VRR hardware inserts one extra scanline just after 
> vactive. So we need to have flipline, vmax, vmin vtotal shifted by 1. 
> This is computed in intel_vrr_extra_vblank_delay()

vmin/vmax/flipline stay put, but we need to account for that extra
scanline when calculating the guadband/pipeline_full.

> 
> For display < 13 hardware expects flipline >= vmin (so we add flipline + 
> 1, not related to vblank delay.
> 
> For some platforms intel_psr_min_vblank_delay() of 1 is required so that 
> moves the vblank start with this amount. we can account for this delay 
> by intel_vrr_real_vblank_delay().

That 1 scaline is just the minimum size for SCL. And once we start
tracking the SCL explicitly then AFAICS pretty much all
intel_vrr_real_vblank_delay() calls can just be replaced with
crtc_state->set_context_latency.

> 
> So for the SCL delay mentioned here should'nt we 
> use intel_vrr_extra_vblank_delay() in the computation below?

I think we should be able to get rid of intel_vrr_extra_vblank_delay()
for the most part. As state we just need to account for it when
calculating the guardband/pipeline_full.

> 
> 
> Regards,
> 
> Ankit
> 
> 
> 
> > Unfortunately this
> > means that one can't simply use these values directly in many places,
> > and instead we always have to go through functions that undo the
> > damage first. This is all rather fragile.
> >
> > Simplify our lives a bit by hiding this mangling deeper inside
> > the low level VRR code, leaving the number stored in the crtc
> > state actually something that humans can use.
> >
> > This does introduce a dependdency as intel_vrr_get_config()
> > will now need to know the SCL value, which is read out in
> > intel_get_transcoder_timings(). I suppose we could simply
> > duplicate the SCL readout in both places should this become
> > a real hinderance. For now just leave a note around the
> > intel_get_transcoder_timings() call to remind us.
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >   drivers/gpu/drm/i915/display/intel_display.c |  4 ++
> >   drivers/gpu/drm/i915/display/intel_vrr.c     | 76 +++++++++++---------
> >   2 files changed, 47 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> > index f4124c79bc83..18b9baa96241 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display.c
> > +++ b/drivers/gpu/drm/i915/display/intel_display.c
> > @@ -3901,6 +3901,10 @@ static bool hsw_get_pipe_config(struct intel_crtc *crtc,
> >   		pipe_config->framestart_delay = 1;
> >   	}
> >   
> > +	/*
> > +	 * intel_vrr_get_config() depends on TRANS_SET_CONTEXT_LATENCY
> > +	 * readout done by intel_get_transcoder_timings().
> > +	 */
> >   	if (!transcoder_is_dsi(pipe_config->cpu_transcoder) ||
> >   	    DISPLAY_VER(display) >= 11)
> >   		intel_get_transcoder_timings(crtc, pipe_config);
> > diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
> > index 71fb64c92165..71a985d00604 100644
> > --- a/drivers/gpu/drm/i915/display/intel_vrr.c
> > +++ b/drivers/gpu/drm/i915/display/intel_vrr.c
> > @@ -156,25 +156,13 @@ static int intel_vrr_vblank_exit_length(const struct intel_crtc_state *crtc_stat
> >   
> >   int intel_vrr_vmin_vtotal(const struct intel_crtc_state *crtc_state)
> >   {
> > -	struct intel_display *display = to_intel_display(crtc_state);
> > -
> >   	/* Min vblank actually determined by flipline */
> > -	if (DISPLAY_VER(display) >= 13)
> > -		return intel_vrr_vmin_flipline(crtc_state);
> > -	else
> > -		return intel_vrr_vmin_flipline(crtc_state) +
> > -			intel_vrr_real_vblank_delay(crtc_state);
> > +	return intel_vrr_vmin_flipline(crtc_state);
> >   }
> >   
> >   int intel_vrr_vmax_vtotal(const struct intel_crtc_state *crtc_state)
> >   {
> > -	struct intel_display *display = to_intel_display(crtc_state);
> > -
> > -	if (DISPLAY_VER(display) >= 13)
> > -		return crtc_state->vrr.vmax;
> > -	else
> > -		return crtc_state->vrr.vmax +
> > -			intel_vrr_real_vblank_delay(crtc_state);
> > +	return crtc_state->vrr.vmax;
> >   }
> >   
> >   int intel_vrr_vmin_vblank_start(const struct intel_crtc_state *crtc_state)
> > @@ -258,6 +246,21 @@ void intel_vrr_compute_vrr_timings(struct intel_crtc_state *crtc_state)
> >   	crtc_state->mode_flags |= I915_MODE_FLAG_VRR;
> >   }
> >   
> > +static int intel_vrr_hw_value(const struct intel_crtc_state *crtc_state,
> > +			      int value)
> > +{
> > +	struct intel_display *display = to_intel_display(crtc_state);
> > +
> > +	/*
> > +	 * On TGL vmin/vmax/flipline also need to be
> > +	 * adjusted by the SCL to maintain correct vtotals.
> > +	 */
> > +	if (DISPLAY_VER(display) >= 13)
> > +		return value;
> > +	else
> > +		return value - intel_vrr_real_vblank_delay(crtc_state);
> > +}
> > +
> >   /*
> >    * For fixed refresh rate mode Vmin, Vmax and Flipline all are set to
> >    * Vtotal value.
> > @@ -265,14 +268,7 @@ void intel_vrr_compute_vrr_timings(struct intel_crtc_state *crtc_state)
> >   static
> >   int intel_vrr_fixed_rr_hw_vtotal(const struct intel_crtc_state *crtc_state)
> >   {
> > -	struct intel_display *display = to_intel_display(crtc_state);
> > -	int crtc_vtotal = crtc_state->hw.adjusted_mode.crtc_vtotal;
> > -
> > -	if (DISPLAY_VER(display) >= 13)
> > -		return crtc_vtotal;
> > -	else
> > -		return crtc_vtotal -
> > -			intel_vrr_real_vblank_delay(crtc_state);
> > +	return intel_vrr_hw_value(crtc_state, crtc_state->hw.adjusted_mode.crtc_vtotal);
> >   }
> >   
> >   static
> > @@ -441,14 +437,6 @@ void intel_vrr_compute_config_late(struct intel_crtc_state *crtc_state)
> >   		crtc_state->vrr.pipeline_full =
> >   			intel_vrr_guardband_to_pipeline_full(crtc_state,
> >   							     crtc_state->vrr.guardband);
> > -
> > -		/*
> > -		 * vmin/vmax/flipline also need to be adjusted by
> > -		 * the vblank delay to maintain correct vtotals.
> > -		 */
> > -		crtc_state->vrr.vmin -= intel_vrr_real_vblank_delay(crtc_state);
> > -		crtc_state->vrr.vmax -= intel_vrr_real_vblank_delay(crtc_state);
> > -		crtc_state->vrr.flipline -= intel_vrr_real_vblank_delay(crtc_state);
> >   	}
> >   }
> >   
> > @@ -607,6 +595,21 @@ void intel_vrr_set_db_point_and_transmission_line(const struct intel_crtc_state
> >   			       EMP_AS_SDP_DB_TL(crtc_state->vrr.vsync_start));
> >   }
> >   
> > +static int intel_vrr_hw_vmin(const struct intel_crtc_state *crtc_state)
> > +{
> > +	return intel_vrr_hw_value(crtc_state, crtc_state->vrr.vmin);
> > +}
> > +
> > +static int intel_vrr_hw_vmax(const struct intel_crtc_state *crtc_state)
> > +{
> > +	return intel_vrr_hw_value(crtc_state, crtc_state->vrr.vmax);
> > +}
> > +
> > +static int intel_vrr_hw_flipline(const struct intel_crtc_state *crtc_state)
> > +{
> > +	return intel_vrr_hw_value(crtc_state, crtc_state->vrr.flipline);
> > +}
> > +
> >   void intel_vrr_enable(const struct intel_crtc_state *crtc_state)
> >   {
> >   	struct intel_display *display = to_intel_display(crtc_state);
> > @@ -616,11 +619,11 @@ void intel_vrr_enable(const struct intel_crtc_state *crtc_state)
> >   		return;
> >   
> >   	intel_de_write(display, TRANS_VRR_VMIN(display, cpu_transcoder),
> > -		       crtc_state->vrr.vmin - 1);
> > +		       intel_vrr_hw_vmin(crtc_state) - 1);
> >   	intel_de_write(display, TRANS_VRR_VMAX(display, cpu_transcoder),
> > -		       crtc_state->vrr.vmax - 1);
> > +		       intel_vrr_hw_vmax(crtc_state) - 1);
> >   	intel_de_write(display, TRANS_VRR_FLIPLINE(display, cpu_transcoder),
> > -		       crtc_state->vrr.flipline - 1);
> > +		       intel_vrr_hw_flipline(crtc_state) - 1);
> >   
> >   	intel_de_write(display, TRANS_PUSH(display, cpu_transcoder),
> >   		       TRANS_PUSH_EN);
> > @@ -754,6 +757,13 @@ void intel_vrr_get_config(struct intel_crtc_state *crtc_state)
> >   		crtc_state->vrr.vmin = intel_de_read(display,
> >   						     TRANS_VRR_VMIN(display, cpu_transcoder)) + 1;
> >   
> > +		if (DISPLAY_VER(display) < 13) {
> > +			/* undo what intel_vrr_hw_value() does when writing the values */
> > +			crtc_state->vrr.flipline += intel_vrr_real_vblank_delay(crtc_state);
> > +			crtc_state->vrr.vmax += intel_vrr_real_vblank_delay(crtc_state);
> > +			crtc_state->vrr.vmin += intel_vrr_real_vblank_delay(crtc_state);
> > +		}
> > +
> >   		/*
> >   		 * For platforms that always use VRR Timing Generator, the VTOTAL.Vtotal
> >   		 * bits are not filled. Since for these platforms TRAN_VMIN is always

-- 
Ville Syrjälä
Intel