Re: [PATCH v3 2/2] drm/i915/dp: BDW cdclk fix for DP audio

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 26 Oct 2016, "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com> wrote:
> On Wed, 2016-10-26 at 11:54 +0300, Jani Nikula wrote:
>> On Wed, 26 Oct 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan@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.
>> >
>> > v3: Combine BDW pixel rate adjustments into a function (Jani)
>> > v2: Restrict fix to BDW
>> >     Retain the set cdclk across modesets (Ville)
>> > Cc: stable@vger.kernel.org
>> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
>> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> 
>> Reviewed-by: Jani Nikula <jani.nikula@intel.com>
>> 
>> We'll need this fix for Skylake too, don't we? Maybe Kabylake? Please
>> send a follow-up patch for Skylake with the changes mentioned inline
>> below.
>> 
>> BR,
>> Jani.
>> 
>> 
>
> Patch 1/2 should take care of gen9 platforms when audio sampling rates
> are <= 96 kHz. I am still not sure how to increase increase cdclk when
> the sampling rates > 96kHZ , that is why I have added the TODO in Patch
> 1/2.

IIUC the two patches and fixes are related, but separate. This one
requires 4 lanes, the other one doesn't. For this one there's no mention
of audio sampling rate.

BR,
Jani.


>
>> > ---
>> >  drivers/gpu/drm/i915/intel_display.c | 27 ++++++++++++++++++++++++---
>> >  1 file changed, 24 insertions(+), 3 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> > index a94f7d1..efe46b4 100644
>> > --- a/drivers/gpu/drm/i915/intel_display.c
>> > +++ b/drivers/gpu/drm/i915/intel_display.c
>> > @@ -10260,6 +10260,27 @@ static void bxt_modeset_commit_cdclk(struct drm_atomic_state *old_state)
>> >  	bxt_set_cdclk(to_i915(dev), req_cdclk);
>> >  }
>> >  
>> > +static int bdw_adjust_min_pipe_pixel_rate(struct intel_crtc_state *crtc_state,
>> > +					  int pixel_rate)
>> > +{
>> > +	/* pixel rate mustn't exceed 95% of cdclk with IPS on BDW */
>> > +	if (crtc_state->ips_enabled)
>> 
>> if (IS_BROADWELL(dev_priv) && 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."
>> > +	 */
>> > +	if (intel_crtc_has_dp_encoder(crtc_state) &&
>> > +	    crtc_state->has_audio &&
>> > +	    crtc_state->port_clock >= 540000 &&
>> > +	    crtc_state->lane_count == 4)
>> > +		pixel_rate = max(432000, pixel_rate);
>> > +
>> > +	return pixel_rate;
>> > +}
>> > +
>> >  /* compute the max rate for new configuration */
>> >  static int ilk_max_pixel_rate(struct drm_atomic_state *state)
>> >  {
>> > @@ -10285,9 +10306,9 @@ static int ilk_max_pixel_rate(struct drm_atomic_state *state)
>> >  
>> >  		pixel_rate = ilk_pipe_pixel_rate(crtc_state);
>> >  
>> > -		/* 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 (IS_BROADWELL(dev_priv))
>> 
>> if (IS_BROADWELL(dev_priv) || IS_SKYLAKE(dev_priv))
>> 
>> > +			pixel_rate = bdw_adjust_min_pipe_pixel_rate(crtc_state,
>> > +								    pixel_rate);
>> >  
>> >  		intel_state->min_pixclk[i] = pixel_rate;
>> >  	}
>> 
>

-- 
Jani Nikula, Intel Open Source Technology Center