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

[Pandiyan, Dhinakaran]

On Tue, 2016-10-25 at 18:19 +0000, Pandiyan, Dhinakaran wrote:
> On Tue, 2016-10-25 at 12:14 +0300, Jani Nikula wrote:
> > On Tue, 25 Oct 2016, Jani Nikula <jani.nikula at intel.com> wrote:
> > > On Tue, 25 Oct 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan at intel.com> 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)
> > >
> > > Cc: stable at vger.kernel.org
> > >
> > >>
> > >> Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan at 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)
> > >> +{
> > >> +
> > >> +	if (intel_crtc_has_dp_encoder(crtc_state) &&
> > >> +	    crtc_state->has_audio &&
> > >> +	    crtc_state->port_clock >= 540000 &&
> > >> +	    crtc_state->lane_count == 4)
> > >> +		return 432000;
> > >
> > > Where does 432000 come from? 450000 or even (337500 + 1). See below.
> > >
> > >> +
> > >> +	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)432
> > >> -			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
> > >
> > > For me the spec says "Do not use DisplayPort with CDCLK 337.5 MHz", not
> > > "less than 432 MHz".
> > 
> > Right, so the spec for *Skylake* mentions 432 MHz. Now, we need this fix
> > for both Broadwell and Skylake, where's the Skylake part?
> > 
> > BR,
> > Jani.
> > 
> > 
> 
> I believe you are looking at CDCLK_CTL that refers to pre-production SKL
> SKU's. See the description for DP_TP_CTL instead. The information seems
> to be scattered a bit
> 
> 
> > >
> > >> +		 * HBR2 (5.4 GHz), or else there may be audio corruption or
> > >> +		 * screen corruption."
> > >> +		 */
> > >> +			pixel_rate = max(pixel_rate,
> > >> +					 bdw_dp_audio_cdclk(crtc_state));
> > >> +		}
> > >
> > > I'd add a new function
> > >
> > > static int bwd_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
> > > 					  int pixel_rate)
> > >
> > > and do both the IPS adjustment and the audio adjustment there, returning
> > > the original pixel_rate if adjustment is not needed. Move the comments
> > > there as well.
> > >
> > > It would be called as
> > >
> > > 	if (IS_BROADWELL(dev_priv))
> > >         	pixel_rate = bwd_adjust_min_pipe_pixel_rate(crtc_state, pixel_rate);
> > >
> > > here.
> > >
> > >
> > > BR,
> > > Jani.
> > >
> 
> Will do.
> 
> -DK
> > >>  
> > >>  		intel_state->min_pixclk[i] = pixel_rate;
> > >>  	}
> > 
> 
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