Re: [PATCH v4 1/2] drm/i915/dp: BDW cdclk fix for DP audio

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

On Tue, 01 Nov 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com> wrote:
> According to BSpec, cdclk for BDW has to be not less than 432 MHz with DP
> audio enabled, port width x4, and link rate HBR2 (5.4 GHz). With cdclk less
> than 432 MHz, enabling audio leads to pipe FIFO underruns and displays
> cycling on/off.
>
> From BSpec:
> "Display» BDW-SKL» dpr» [Register] DP_TP_CTL [BDW+,EXCLUDE(CHV)]
> Workaround : 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."
>
> Since, some DP configurations (e.g., MST) use port width x4 and HBR2
> link rate, let's increase the cdclk to >= 432 MHz to enable audio for those
> cases.
>
> v4: Changed commit message
> 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>

Yup.

> ---
>  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 895b3dc..37483ee 100644
> --- a/drivers/gpu/drm/i915/intel_display.c
> +++ b/drivers/gpu/drm/i915/intel_display.c
> @@ -10261,6 +10261,27 @@ 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)
> +		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)
>  {
> @@ -10286,9 +10307,9 @@ 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))
> +			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
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