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

[Jani Nikula]

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)
>> -			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.


>
>> +		 * 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.
>
>>  
>>  		intel_state->min_pixclk[i] = pixel_rate;
>>  	}

-- 
Jani Nikula, Intel Open Source Technology Center