Re: [PATCH 11/14] drm/i915: Fallback to lower link rate and lane count during link training

[Jim Bride <jim.bride@linux.intel.com>]

On Fri, Sep 02, 2016 at 07:52:53PM +0000, Pandiyan, Dhinakaran wrote:
> On Thu, 2016-09-01 at 15:08 -0700, Manasi Navare wrote:
> > According to the DisplayPort Spec, in case of Clock Recovery failure
> > the link training sequence should fall back to the lower link rate
> > followed by lower lane count until CR succeeds.
> > On CR success, the sequence proceeds with Channel EQ.
> > In case of Channel EQ failures, it should fallback to
> > lower link rate and lane count and start the CR phase again.
> > 
> > Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_ddi.c              | 109 +++++++++++++++++++++++---
> >  drivers/gpu/drm/i915/intel_dp_link_training.c |  12 ++-
> >  drivers/gpu/drm/i915/intel_drv.h              |   4 +-
> >  3 files changed, 110 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> > index 67a6a0b..78d6687 100644
> > --- a/drivers/gpu/drm/i915/intel_ddi.c
> > +++ b/drivers/gpu/drm/i915/intel_ddi.c
> > @@ -1634,29 +1634,50 @@ void intel_ddi_clk_select(struct intel_encoder *encoder,
> >  	}
> >  }
> >  
> > -static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
> > +static void intel_ddi_pre_enable_edp(struct intel_encoder *encoder,
> >  				    int link_rate, uint32_t lane_count,
> > -				    struct intel_shared_dpll *pll,
> > -				    bool link_mst)
> > +				    struct intel_shared_dpll *pll)
> >  {
> >  	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
> >  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> >  	enum port port = intel_ddi_get_encoder_port(encoder);
> >  
> >  	intel_dp_set_link_params(intel_dp, link_rate, lane_count,
> > -				 link_mst);
> > -	if (encoder->type == INTEL_OUTPUT_EDP)
> > -		intel_edp_panel_on(intel_dp);
> > +				 false);
> > +
> > +	intel_edp_panel_on(intel_dp);
> >  
> >  	intel_ddi_clk_select(encoder, pll);
> >  	intel_prepare_dp_ddi_buffers(encoder);
> >  	intel_ddi_init_dp_buf_reg(encoder);
> >  	intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> >  	intel_dp_start_link_train(intel_dp);
> > -	if (port != PORT_A || INTEL_GEN(dev_priv) >= 9)
> > +	if (port != PORT_A || INTEL_INFO(dev_priv)->gen >= 9)
> >  		intel_dp_stop_link_train(intel_dp);
> >  }
> >  
> > +static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
> > +				    int link_rate, uint32_t lane_count,
> > +				    struct intel_shared_dpll *pll,
> > +				    bool link_mst)
> > +{
> > +	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
> > +	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> > +	struct intel_shared_dpll_config tmp_pll_config;
> > +
> > +	/* Disable the PLL and obtain the PLL for Link Training
> > +	 * that starts with highest link rate and lane count.
> > +	 */
> > +	tmp_pll_config = pll->config;
> > +	pll->funcs.disable(dev_priv, pll);
> > +	pll->config.crtc_mask = 0;
> > +
> > +	/* If Link Training fails, send a uevent to generate a hotplug */
> > +	if (!(intel_ddi_link_train(intel_dp, link_rate, lane_count, link_mst)))
> > +		drm_kms_helper_hotplug_event(encoder->base.dev);
> > +	pll->config = tmp_pll_config;
> > +}
> > +
> >  static void intel_ddi_pre_enable_hdmi(struct intel_encoder *encoder,
> >  				      bool has_hdmi_sink,
> >  				      struct drm_display_mode *adjusted_mode,
> > @@ -1690,20 +1711,26 @@ static void intel_ddi_pre_enable(struct intel_encoder *intel_encoder,
> >  	struct intel_crtc *crtc = to_intel_crtc(encoder->crtc);
> >  	int type = intel_encoder->type;
> >  
> > -	if (type == INTEL_OUTPUT_DP || type == INTEL_OUTPUT_EDP) {
> > +	if (type == INTEL_OUTPUT_EDP)
> > +		intel_ddi_pre_enable_edp(intel_encoder,
> > +					crtc->config->port_clock,
> > +					crtc->config->lane_count,
> > +					crtc->config->shared_dpll);
> > +
> > +	if (type == INTEL_OUTPUT_DP)
> >  		intel_ddi_pre_enable_dp(intel_encoder,
> >  					crtc->config->port_clock,
> >  					crtc->config->lane_count,
> >  					crtc->config->shared_dpll,
> >  					intel_crtc_has_type(crtc->config,
> >  							    INTEL_OUTPUT_DP_MST));
> > -	}
> > -	if (type == INTEL_OUTPUT_HDMI) {
> > +
> > +	if (type == INTEL_OUTPUT_HDMI)
> >  		intel_ddi_pre_enable_hdmi(intel_encoder,
> >  					  crtc->config->has_hdmi_sink,
> >  					  &crtc->config->base.adjusted_mode,
> >  					  crtc->config->shared_dpll);
> > -	}
> > +
> >  }
> >  
> >  static void intel_ddi_post_disable(struct intel_encoder *intel_encoder,
> > @@ -2431,6 +2458,66 @@ intel_ddi_get_link_dpll(struct intel_dp *intel_dp, int clock)
> >  	return pll;
> >  }
> >  
> > +bool
> > +intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
> > +		    uint8_t max_lane_count, bool link_mst)
> > +{
> > +	struct intel_connector *connector = intel_dp->attached_connector;
> > +	struct intel_encoder *encoder = connector->encoder;
> > +	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> > +	struct intel_shared_dpll *pll;
> > +	struct intel_shared_dpll_config tmp_pll_config;
> > +	int link_rate;
> > +	uint8_t lane_count;
> > +	bool link_rate_not_found = true;
> > +	bool ret = false;
> > +
> > +	for (lane_count = max_lane_count; lane_count > 0; lane_count >>= 1) {
> > +
> > +		link_rate = max_link_rate;
> > +		while (link_rate_not_found) {
> > +			pll = intel_ddi_get_link_dpll(intel_dp, link_rate);
> > +			if (pll == NULL) {
> > +				DRM_ERROR("Could not find DPLL for link "
> > +					  "training.\n");
> > +				return false;
> > +			}
> > +			tmp_pll_config = pll->config;
> > +			pll->funcs.enable(dev_priv, pll);
> > +
> > +			intel_dp_set_link_params(intel_dp, link_rate,
> > +						 lane_count, link_mst);
> > +
> > +			intel_ddi_clk_select(encoder, pll);
> > +			intel_prepare_dp_ddi_buffers(encoder);
> > +			intel_ddi_init_dp_buf_reg(encoder);
> > +			intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
> > +			ret = intel_dp_start_link_train(intel_dp);
> > +			if (ret)
> > +				break;
> > +
> > +			/* Disable port followed by PLL for next retry/clean up */
> > +			intel_ddi_post_disable(encoder, NULL, NULL);
> > +			pll->funcs.disable(dev_priv, pll);
> > +			if (link_rate == 540000)
> > +				link_rate = 270000;
> > +			else if (link_rate == 270000)
> > +				link_rate = 162000;
> > +			else
> > +				link_rate_not_found = false;
> 
> 1. Aren't the supported rates platform dependent? I see these
> definitions in intel_dp.c
> 
> static const int bxt_rates[] = { 162000, 216000, 243000, 270000,
>                                   324000, 432000, 540000 };
> static const int skl_rates[] = { 162000, 216000, 270000,
>                                   324000, 432000, 540000 };
> 
> 
> 2. Also, it is good to have the standard rates defined in a array within
> a header instead of having literals here.
> 
> Or even better, re-use what's available in intel_dp.c
> static const int default_rates[] = { 162000, 270000, 540000 };

Actually, we should be fetching and using the common rates here.  There's
already code to take the union of what the source and sink support.

Jim


> 
> > +		}
> > +		if (ret) {
> > +			DRM_DEBUG_KMS("Link Training successful\n");
> > +			intel_dp_stop_link_train(intel_dp);
> > +			break;
> > +		}
> > +	}
> > +	if (!lane_count)
> > +		DRM_ERROR("Link Training Failed\n");
> > +
> > +	return ret;
> > +}
> > +
> >  void intel_ddi_init(struct drm_device *dev, enum port port)
> >  {
> >  	struct drm_i915_private *dev_priv = to_i915(dev);
> > diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > index 07f0159..0df49e8 100644
> > --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> > +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> > @@ -309,9 +309,15 @@ void intel_dp_stop_link_train(struct intel_dp *intel_dp)
> >  				DP_TRAINING_PATTERN_DISABLE);
> >  }
> >  
> > -void
> > +bool
> >  intel_dp_start_link_train(struct intel_dp *intel_dp)
> >  {
> > -	intel_dp_link_training_clock_recovery(intel_dp);
> > -	intel_dp_link_training_channel_equalization(intel_dp);
> > +	bool ret;
> > +
> > +	if (intel_dp_link_training_clock_recovery(intel_dp)) {
> > +		ret = intel_dp_link_training_channel_equalization(intel_dp);
> > +		if (ret)
> > +			return true;
> > +	}
> > +	return false;
> >  }
> > diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> > index e5bc976..342a2d5 100644
> > --- a/drivers/gpu/drm/i915/intel_drv.h
> > +++ b/drivers/gpu/drm/i915/intel_drv.h
> > @@ -1160,6 +1160,8 @@ void intel_ddi_clock_get(struct intel_encoder *encoder,
> >  			 struct intel_crtc_state *pipe_config);
> >  void intel_ddi_set_vc_payload_alloc(struct drm_crtc *crtc, bool state);
> >  uint32_t ddi_signal_levels(struct intel_dp *intel_dp);
> > +bool intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
> > +			 uint8_t max_lane_count, bool link_mst);
> >  struct intel_shared_dpll *intel_ddi_get_link_dpll(struct intel_dp *intel_dp,
> >  						  int clock);
> >  unsigned int intel_fb_align_height(struct drm_device *dev,
> > @@ -1381,7 +1383,7 @@ bool intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
> >  void intel_dp_set_link_params(struct intel_dp *intel_dp,
> >  			      int link_rate, uint8_t lane_count,
> >  			      bool link_mst);
> > -void intel_dp_start_link_train(struct intel_dp *intel_dp);
> > +bool intel_dp_start_link_train(struct intel_dp *intel_dp);
> >  void intel_dp_stop_link_train(struct intel_dp *intel_dp);
> >  void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
> >  void intel_dp_encoder_reset(struct drm_encoder *encoder);
> 
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