Re: [PATCH v2 2/2] drm/i915/dp: BDW cdclk fix for DP audio

["Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com>]

On Tue, 2016-10-25 at 11:46 +0300, Ville Syrjälä wrote:
> On Mon, Oct 24, 2016 at 09:18:37PM -0700, Dhinakaran Pandiyan wrote:
> > According to BSpec, cdclk has to be not less than 432 MHz with DP audio
> > enabled, port width x4, and link rate HBR2 (5.4 GHz)
> > 
> > Having a lower cdclk triggers pipe underruns, which then lead to displays
> > continuously cycling off and on. This is essential for DP MST audio as the
> > link is trained at HBR2 and 4 lanes by default.
> > 
> > v2: Restrict fix to BDW
> >     Retain the set cdclk across modesets (Ville)
> > 
> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_display.c | 28 +++++++++++++++++++++++++---
> >  1 file changed, 25 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > index a94f7d1..8c59651 100644
> > --- a/drivers/gpu/drm/i915/intel_display.c
> > +++ b/drivers/gpu/drm/i915/intel_display.c
> > @@ -10260,6 +10260,18 @@ static void bxt_modeset_commit_cdclk(struct drm_atomic_state *old_state)
> >  	bxt_set_cdclk(to_i915(dev), req_cdclk);
> >  }
> >  
> > +static unsigned int bdw_dp_audio_cdclk(struct intel_crtc_state *crtc_state)
> > +{
> > +
> 
> Useless blank line.
> 
> > +	if (intel_crtc_has_dp_encoder(crtc_state) &&
> > +	    crtc_state->has_audio &&
> > +	    crtc_state->port_clock >= 540000 &&
> > +	    crtc_state->lane_count == 4)
> > +		return 432000;
> > +
> > +	return 0;
> > +}
> > +
> >  /* compute the max rate for new configuration */
> >  static int ilk_max_pixel_rate(struct drm_atomic_state *state)
> >  {
> > @@ -10275,7 +10287,7 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
> >  	       sizeof(intel_state->min_pixclk));
> >  
> >  	for_each_crtc_in_state(state, crtc, cstate, i) {
> > -		int pixel_rate;
> > +		unsigned int pixel_rate;
> >  
> >  		crtc_state = to_intel_crtc_state(cstate);
> >  		if (!crtc_state->base.enable) {
> > @@ -10285,9 +10297,19 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
> >  
> >  		pixel_rate = ilk_pipe_pixel_rate(crtc_state);
> >  
> > +		if (IS_BROADWELL(dev_priv)) {
> >  		/* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
> > -		if (IS_BROADWELL(dev_priv) && crtc_state->ips_enabled)
> > -			pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
> > +			if (crtc_state->ips_enabled)
> > +				pixel_rate = DIV_ROUND_UP(pixel_rate * 100, 95);
> > +
> > +		/* BSpec says "Do not use DisplayPort with CDCLK less than
> > +		 * 432 MHz, audio enabled, port width x4, and link rate
> > +		 * HBR2 (5.4 GHz), or else there may be audio corruption or
> > +		 * screen corruption."
> > +		 */
> 
> Indentation of the comments is wrong.
> 
> > +			pixel_rate = max(pixel_rate,
> > +					 bdw_dp_audio_cdclk(crtc_state));
> > +		}
> >  
> >  		intel_state->min_pixclk[i] = pixel_rate;
> 
> Otherwise I suppose this ought to work.
> 
> So with the formatting stuff fixed this is
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> The whole min_pixclk vs. pixel_rate vs. cdclk thing is a bit of a mess
> though. So it could use a thorough cleaning to make it less confusing.
> I'm tinking we might just want to start tracking a minimum acceptable
> cdclk per pipe. Probably the main thing would be to pull in the
> 5%/10% guardband handling here for all platforms.
> 

Yeah, definitely needs some work. As you wrote in the previous review,
we can get rid of tracking min_pixclk and track min_cdclk instead. I
could not find any other use for min_pixclk other than computing cdclk.
 
Thanks for the review.

-DK

> >  	}
> > -- 
> > 2.7.4
> 

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