Re: [PATCH v18 5/6] drm/i915/dp: Enable Upfront link training on DDI platforms

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

On Wed, 21 Sep 2016, Manasi Navare <manasi.d.navare@intel.com> wrote:
> To support USB type C alternate DP mode, the display driver needs to
> know the number of lanes required by the DP panel as well as number
> of lanes that can be supported by the type-C cable. Sometimes, the
> type-C cable may limit the bandwidth even if Panel can support
> more lanes. To address these scenarios we need to train the link before
> modeset. This upfront link training caches the values of max link rate
> and max lane count that get used later during modeset. Upfront link
> training does not change any HW state, the link is disabled and PLL
> values are reset to previous values after upfront link tarining so
> that subsequent modeset is not aware of these changes.

I think we should call timeout on this patch, and focus on the DP
compliance parts first. Frankly, I think this patch is really scary. If
I got a bisect result for a regression on this, I would have absolutely
no clue what exactly caused it.

Please correct me if you think I'm wrong, but I don't think upfront link
training is strictly required for DP compliance. (Conversely, if you
think this is required for DP compliance, the rationale is absolutely
required in the commit message in more than just a few words.)

BR,
Jani.


>
> This patch is based on prior work done by
> R,Durgadoss <durgadoss.r@intel.com>
>
> Changes since v17:
> * Rebased on the latest nightly
> Changes since v16:
> * Use HAS_DDI macro for enabling this feature (Rodrigo Vivi)
> * Fix some unnecessary removals/changes due to rebase (Rodrigo Vivi)
>
> Changes since v15:
> * Split this patch into two patches - one with functional
> changes to enable upfront and other with moving the existing
> functions around so that they can be used for upfront (Jani Nikula)
> * Cleaned up the commit message
>
> Signed-off-by: Durgadoss R <durgadoss.r@intel.com>
> Signed-off-by: Jim Bride <jim.bride@linux.intel.com>
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c              |  21 ++-
>  drivers/gpu/drm/i915/intel_dp.c               | 190 +++++++++++++++++++++++++-
>  drivers/gpu/drm/i915/intel_dp_link_training.c |   1 -
>  drivers/gpu/drm/i915/intel_drv.h              |  14 +-
>  4 files changed, 218 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index 093038c..8e52507 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -1676,7 +1676,8 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
>  	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))
> +	if (!intel_ddi_link_train(intel_dp, link_rate, lane_count, link_mst,
> +				  false))
>  		drm_kms_helper_hotplug_event(encoder->base.dev);
>  	pll->config = tmp_pll_config;
>  }
> @@ -2464,7 +2465,7 @@ intel_ddi_get_link_dpll(struct intel_dp *intel_dp, int clock)
>  
>  bool
>  intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
> -		     uint8_t max_lane_count, bool link_mst)
> +		     uint8_t max_lane_count, bool link_mst, bool is_upfront)
>  {
>  	struct intel_connector *connector = intel_dp->attached_connector;
>  	struct intel_encoder *encoder = connector->encoder;
> @@ -2513,6 +2514,7 @@ intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
>  			pll->funcs.disable(dev_priv, pll);
>  			pll->config = tmp_pll_config;
>  		}
> +
>  		if (ret) {
>  			DRM_DEBUG_KMS("Link Training successful at link rate: %d lane: %d\n",
>  				      link_rate, lane_count);
> @@ -2522,6 +2524,21 @@ intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
>  
>  	intel_dp_stop_link_train(intel_dp);
>  
> +	if (is_upfront) {
> +		DRM_DEBUG_KMS("Upfront link train %s: link_clock:%d lanes:%d\n",
> +			      ret ? "Passed" : "Failed",
> +			      link_rate, lane_count);
> +		/* Disable port followed by PLL for next retry/clean up */
> +		intel_ddi_post_disable(encoder, NULL, NULL);
> +		pll->funcs.disable(dev_priv, pll);
> +		pll->config = tmp_pll_config;
> +		if (ret) {
> +			/* Save the upfront values */
> +			intel_dp->max_lanes_upfront = lane_count;
> +			intel_dp->max_link_rate_upfront = link_rate;
> +		}
> +	}
> +
>  	if (!lane_count)
>  		DRM_ERROR("Link Training Failed\n");
>  
> diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> index 8d9a8ab..a058d5d 100644
> --- a/drivers/gpu/drm/i915/intel_dp.c
> +++ b/drivers/gpu/drm/i915/intel_dp.c
> @@ -153,12 +153,21 @@ intel_dp_max_link_bw(struct intel_dp  *intel_dp)
>  static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp)
>  {
>  	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> -	u8 source_max, sink_max;
> +	u8 temp, source_max, sink_max;
>  
>  	source_max = intel_dig_port->max_lanes;
>  	sink_max = drm_dp_max_lane_count(intel_dp->dpcd);
>  
> -	return min(source_max, sink_max);
> +	temp = min(source_max, sink_max);
> +
> +	/*
> +	 * Limit max lanes w.r.t to the max value found
> +	 * using Upfront link training also.
> +	 */
> +	if (intel_dp->max_lanes_upfront)
> +		return min(temp, intel_dp->max_lanes_upfront);
> +	else
> +		return temp;
>  }
>  
>  /*
> @@ -190,6 +199,42 @@ intel_dp_max_data_rate(int max_link_clock, int max_lanes)
>  	return (max_link_clock * max_lanes * 8) / 10;
>  }
>  
> +static int intel_dp_upfront_crtc_disable(struct intel_crtc *crtc,
> +					 struct drm_modeset_acquire_ctx *ctx,
> +					 bool enable)
> +{
> +	int ret;
> +	struct drm_atomic_state *state;
> +	struct intel_crtc_state *crtc_state;
> +	struct drm_device *dev = crtc->base.dev;
> +	enum pipe pipe = crtc->pipe;
> +
> +	state = drm_atomic_state_alloc(dev);
> +	if (!state)
> +		return -ENOMEM;
> +
> +	state->acquire_ctx = ctx;
> +
> +	crtc_state = intel_atomic_get_crtc_state(state, crtc);
> +	if (IS_ERR(crtc_state)) {
> +		ret = PTR_ERR(crtc_state);
> +		drm_atomic_state_free(state);
> +		return ret;
> +	}
> +
> +	DRM_DEBUG_KMS("%sabling crtc %c %s upfront link train\n",
> +			enable ? "En" : "Dis",
> +			pipe_name(pipe),
> +			enable ? "after" : "before");
> +
> +	crtc_state->base.active = enable;
> +	ret = drm_atomic_commit(state);
> +	if (ret)
> +		drm_atomic_state_free(state);
> +
> +	return ret;
> +}
> +
>  static int
>  intel_dp_downstream_max_dotclock(struct intel_dp *intel_dp)
>  {
> @@ -281,6 +326,17 @@ static int intel_dp_common_rates(struct intel_dp *intel_dp,
>  	int source_len, sink_len;
>  
>  	sink_len = intel_dp_sink_rates(intel_dp, &sink_rates);
> +
> +	/* Cap sink rates w.r.t upfront values */
> +	if (intel_dp->max_link_rate_upfront) {
> +		int len = sink_len - 1;
> +
> +		while (len > 0 && sink_rates[len] >
> +		       intel_dp->max_link_rate_upfront)
> +			len--;
> +		sink_len = len + 1;
> +	}
> +
>  	source_len = intel_dp_source_rates(intel_dp, &source_rates);
>  
>  	return intersect_rates(source_rates, source_len,
> @@ -288,6 +344,92 @@ static int intel_dp_common_rates(struct intel_dp *intel_dp,
>  			       common_rates);
>  }
>  
> +static bool intel_dp_upfront_link_train(struct intel_dp *intel_dp)
> +{
> +	struct intel_digital_port *intel_dig_port = dp_to_dig_port(intel_dp);
> +	struct intel_encoder *intel_encoder = &intel_dig_port->base;
> +	struct drm_device *dev = intel_encoder->base.dev;
> +	struct drm_i915_private *dev_priv = to_i915(dev);
> +	struct drm_mode_config *config = &dev->mode_config;
> +	struct drm_modeset_acquire_ctx ctx;
> +	struct intel_crtc *intel_crtc;
> +	struct drm_crtc *crtc = NULL;
> +	struct intel_shared_dpll *pll;
> +	struct intel_shared_dpll_config tmp_pll_config;
> +	bool disable_dpll = false;
> +	int ret;
> +	bool done = false, has_mst = false;
> +	uint8_t max_lanes;
> +	int common_rates[DP_MAX_SUPPORTED_RATES] = {};
> +	int common_len;
> +	enum intel_display_power_domain power_domain;
> +
> +	power_domain = intel_display_port_power_domain(intel_encoder);
> +	intel_display_power_get(dev_priv, power_domain);
> +
> +	common_len = intel_dp_common_rates(intel_dp, common_rates);
> +	max_lanes = intel_dp_max_lane_count(intel_dp);
> +	if (WARN_ON(common_len <= 0))
> +		return true;
> +
> +	drm_modeset_acquire_init(&ctx, 0);
> +retry:
> +	ret = drm_modeset_lock(&config->connection_mutex, &ctx);
> +	if (ret)
> +		goto exit_fail;
> +
> +	if (intel_encoder->base.crtc) {
> +		crtc = intel_encoder->base.crtc;
> +
> +		ret = drm_modeset_lock(&crtc->mutex, &ctx);
> +		if (ret)
> +			goto exit_fail;
> +
> +		ret = drm_modeset_lock(&crtc->primary->mutex, &ctx);
> +		if (ret)
> +			goto exit_fail;
> +
> +		intel_crtc = to_intel_crtc(crtc);
> +		pll = intel_crtc->config->shared_dpll;
> +		disable_dpll = true;
> +		has_mst = intel_crtc_has_type(intel_crtc->config,
> +					      INTEL_OUTPUT_DP_MST);
> +		ret = intel_dp_upfront_crtc_disable(intel_crtc, &ctx, false);
> +		if (ret)
> +			goto exit_fail;
> +	}
> +
> +	mutex_lock(&dev_priv->dpll_lock);
> +	if (disable_dpll) {
> +		/* Clear the PLL config state */
> +		tmp_pll_config = pll->config;
> +		pll->config.crtc_mask = 0;
> +	}
> +
> +	done = intel_dp->upfront_link_train(intel_dp,
> +					    common_rates[common_len-1],
> +					    max_lanes,
> +					    has_mst,
> +					    true);
> +	if (disable_dpll)
> +		pll->config = tmp_pll_config;
> +
> +	mutex_unlock(&dev_priv->dpll_lock);
> +
> +	if (crtc)
> +		ret = intel_dp_upfront_crtc_disable(intel_crtc, &ctx, true);
> +
> +exit_fail:
> +	if (ret == -EDEADLK) {
> +		drm_modeset_backoff(&ctx);
> +		goto retry;
> +	}
> +	drm_modeset_drop_locks(&ctx);
> +	drm_modeset_acquire_fini(&ctx);
> +	intel_display_power_put(dev_priv, power_domain);
> +	return done;
> +}
> +
>  static enum drm_mode_status
>  intel_dp_mode_valid(struct drm_connector *connector,
>  		    struct drm_display_mode *mode)
> @@ -311,6 +453,19 @@ intel_dp_mode_valid(struct drm_connector *connector,
>  		target_clock = fixed_mode->clock;
>  	}
>  
> +	if (intel_dp->upfront_link_train && !intel_dp->upfront_done) {
> +		bool do_upfront_link_train;
> +		/* Do not do upfront link train, if it is a compliance
> +		 * request
> +		 */
> +		do_upfront_link_train = !intel_dp->upfront_done &&
> +			(intel_dp->compliance_test_type !=
> +			 DP_TEST_LINK_TRAINING);
> +
> +		if (do_upfront_link_train)
> +			intel_dp->upfront_done = intel_dp_upfront_link_train(intel_dp);
> +	}
> +
>  	max_link_clock = intel_dp_max_link_rate(intel_dp);
>  	max_lanes = intel_dp_max_lane_count(intel_dp);
>  
> @@ -1499,6 +1654,9 @@ intel_dp_max_link_rate(struct intel_dp *intel_dp)
>  	int rates[DP_MAX_SUPPORTED_RATES] = {};
>  	int len;
>  
> +	if (intel_dp->max_link_rate_upfront)
> +		return intel_dp->max_link_rate_upfront;
> +
>  	len = intel_dp_common_rates(intel_dp, rates);
>  	if (WARN_ON(len <= 0))
>  		return 162000;
> @@ -1644,6 +1802,21 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>  	for (; bpp >= 6*3; bpp -= 2*3) {
>  		mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
>  						   bpp);
> +
> +		if (!is_edp(intel_dp) && intel_dp->upfront_done) {
> +			clock = max_clock;
> +			lane_count = intel_dp->max_lanes_upfront;
> +			link_clock = intel_dp->max_link_rate_upfront;
> +			link_avail = intel_dp_max_data_rate(link_clock,
> +							    lane_count);
> +			mode_rate = intel_dp_link_required(adjusted_mode->crtc_clock,
> +							   bpp);
> +			if (mode_rate <= link_avail)
> +				goto found;
> +			else
> +				continue;
> +		}
> +
>  		clock = max_clock;
>  		lane_count = max_lane_count;
>  		link_clock = common_rates[clock];
> @@ -1672,7 +1845,6 @@ found:
>  	}
>  
>  	pipe_config->lane_count = lane_count;
> -
>  	pipe_config->pipe_bpp = bpp;
>  	pipe_config->port_clock = common_rates[clock];
>  
> @@ -4453,8 +4625,12 @@ intel_dp_long_pulse(struct intel_connector *intel_connector)
>  
>  out:
>  	if ((status != connector_status_connected) &&
> -	    (intel_dp->is_mst == false))
> +	    (intel_dp->is_mst == false)) {
>  		intel_dp_unset_edid(intel_dp);
> +		intel_dp->upfront_done = false;
> +		intel_dp->max_lanes_upfront = 0;
> +		intel_dp->max_link_rate_upfront = 0;
> +	}
>  
>  	intel_display_power_put(to_i915(dev), power_domain);
>  	return;
> @@ -5698,6 +5874,12 @@ intel_dp_init_connector(struct intel_digital_port *intel_dig_port,
>  	if (type == DRM_MODE_CONNECTOR_eDP)
>  		intel_encoder->type = INTEL_OUTPUT_EDP;
>  
> +	/* Initialize upfront link training vfunc for DP */
> +	if (intel_encoder->type != INTEL_OUTPUT_EDP) {
> +		if (HAS_DDI(dev_priv))
> +			intel_dp->upfront_link_train = intel_ddi_link_train;
> +	}
> +
>  	/* eDP only on port B and/or C on vlv/chv */
>  	if (WARN_ON((IS_VALLEYVIEW(dev) || IS_CHERRYVIEW(dev)) &&
>  		    is_edp(intel_dp) && port != PORT_B && port != PORT_C))
> diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
> index 6eb5eb6..782a919 100644
> --- a/drivers/gpu/drm/i915/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
> @@ -304,7 +304,6 @@ intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
>  	intel_dp_set_idle_link_train(intel_dp);
>  
>  	return intel_dp->channel_eq_status;
> -
>  }
>  
>  void intel_dp_stop_link_train(struct intel_dp *intel_dp)
> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> index 0aeb317..fdfc0b6 100644
> --- a/drivers/gpu/drm/i915/intel_drv.h
> +++ b/drivers/gpu/drm/i915/intel_drv.h
> @@ -887,6 +887,12 @@ struct intel_dp {
>  	enum hdmi_force_audio force_audio;
>  	bool limited_color_range;
>  	bool color_range_auto;
> +
> +	/* Upfront link train parameters */
> +	int max_link_rate_upfront;
> +	uint8_t max_lanes_upfront;
> +	bool upfront_done;
> +
>  	uint8_t dpcd[DP_RECEIVER_CAP_SIZE];
>  	uint8_t psr_dpcd[EDP_PSR_RECEIVER_CAP_SIZE];
>  	uint8_t downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
> @@ -944,6 +950,11 @@ struct intel_dp {
>  	/* This is called before a link training is starterd */
>  	void (*prepare_link_retrain)(struct intel_dp *intel_dp);
>  
> +	/* For Upfront link training */
> +	bool (*upfront_link_train)(struct intel_dp *intel_dp, int clock,
> +				   uint8_t lane_count, bool link_mst,
> +				   bool is_upfront);
> +
>  	/* Displayport compliance testing */
>  	unsigned long compliance_test_type;
>  	unsigned long compliance_test_data;
> @@ -1166,7 +1177,8 @@ void intel_ddi_clock_get(struct intel_encoder *encoder,
>  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);
> +			  uint8_t max_lane_count, bool link_mst,
> +			  bool is_upfront);
>  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,

-- 
Jani Nikula, Intel Open Source Technology Center
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