drivers/gpu/drm/i915/display/intel_dp_link_training.c - linux - Git at Google

 /*
  * Copyright © 2008-2015 Intel Corporation
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
  * to deal in the Software without restriction, including without limitation
  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  * and/or sell copies of the Software, and to permit persons to whom the
  * Software is furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice (including the next
  * paragraph) shall be included in all copies or substantial portions of the
  * Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  */

 #include "intel_display_types.h"
 #include "intel_dp.h"
 #include "intel_dp_link_training.h"

 static void
 intel_dp_dump_link_status(const u8 link_status[DP_LINK_STATUS_SIZE])
 {

 	DRM_DEBUG_KMS("ln0_1:0x%x ln2_3:0x%x align:0x%x sink:0x%x adj_req0_1:0x%x adj_req2_3:0x%x",
 		      link_status[0], link_status[1], link_status[2],
 		      link_status[3], link_status[4], link_status[5]);
 }

 static u8 dp_voltage_max(u8 preemph)
 {
 	switch (preemph & DP_TRAIN_PRE_EMPHASIS_MASK) {
 	case DP_TRAIN_PRE_EMPH_LEVEL_0:
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
 	case DP_TRAIN_PRE_EMPH_LEVEL_1:
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_2;
 	case DP_TRAIN_PRE_EMPH_LEVEL_2:
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_1;
 	case DP_TRAIN_PRE_EMPH_LEVEL_3:
 	default:
 		return DP_TRAIN_VOLTAGE_SWING_LEVEL_0;
 	}
 }

 void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
 			       const u8 link_status[DP_LINK_STATUS_SIZE])
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	u8 v = 0;
 	u8 p = 0;
 	int lane;
 	u8 voltage_max;
 	u8 preemph_max;

 	for (lane = 0; lane < intel_dp->lane_count; lane++) {
 		v = max(v, drm_dp_get_adjust_request_voltage(link_status, lane));
 		p = max(p, drm_dp_get_adjust_request_pre_emphasis(link_status, lane));
 	}

 	preemph_max = intel_dp->preemph_max(intel_dp);
 	drm_WARN_ON_ONCE(&i915->drm,
 			 preemph_max != DP_TRAIN_PRE_EMPH_LEVEL_2 &&
 			 preemph_max != DP_TRAIN_PRE_EMPH_LEVEL_3);

 	if (p >= preemph_max)
 		p = preemph_max | DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;

 	v = min(v, dp_voltage_max(p));

 	voltage_max = intel_dp->voltage_max(intel_dp);
 	drm_WARN_ON_ONCE(&i915->drm,
 			 voltage_max != DP_TRAIN_VOLTAGE_SWING_LEVEL_2 &&
 			 voltage_max != DP_TRAIN_VOLTAGE_SWING_LEVEL_3);

 	if (v >= voltage_max)
 		v = voltage_max | DP_TRAIN_MAX_SWING_REACHED;

 	for (lane = 0; lane < 4; lane++)
 		intel_dp->train_set[lane] = v | p;
 }

 static bool
 intel_dp_set_link_train(struct intel_dp *intel_dp,
 			u8 dp_train_pat)
 {
 	u8 buf[sizeof(intel_dp->train_set) + 1];
 	int ret, len;

 	intel_dp_program_link_training_pattern(intel_dp, dp_train_pat);

 	buf[0] = dp_train_pat;
 	if ((dp_train_pat & DP_TRAINING_PATTERN_MASK) ==
 	    DP_TRAINING_PATTERN_DISABLE) {
 		/* don't write DP_TRAINING_LANEx_SET on disable */
 		len = 1;
 	} else {
 		/* DP_TRAINING_LANEx_SET follow DP_TRAINING_PATTERN_SET */
 		memcpy(buf + 1, intel_dp->train_set, intel_dp->lane_count);
 		len = intel_dp->lane_count + 1;
 	}

 	ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_PATTERN_SET,
 				buf, len);

 	return ret == len;
 }

 static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			u8 dp_train_pat)
 {
 	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
 	intel_dp_set_signal_levels(intel_dp);
 	return intel_dp_set_link_train(intel_dp, dp_train_pat);
 }

 static bool
 intel_dp_update_link_train(struct intel_dp *intel_dp)
 {
 	int ret;

 	intel_dp_set_signal_levels(intel_dp);

 	ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_LANE0_SET,
 				intel_dp->train_set, intel_dp->lane_count);

 	return ret == intel_dp->lane_count;
 }

 static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
 {
 	int lane;

 	for (lane = 0; lane < intel_dp->lane_count; lane++)
 		if ((intel_dp->train_set[lane] &
 		     DP_TRAIN_MAX_SWING_REACHED) == 0)
 			return false;

 	return true;
 }

 /* Enable corresponding port and start training pattern 1 */
 static bool
 intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	u8 voltage;
 	int voltage_tries, cr_tries, max_cr_tries;
 	bool max_vswing_reached = false;
 	u8 link_config[2];
 	u8 link_bw, rate_select;

 	if (intel_dp->prepare_link_retrain)
 		intel_dp->prepare_link_retrain(intel_dp);

 	intel_dp_compute_rate(intel_dp, intel_dp->link_rate,
 			      &link_bw, &rate_select);

 	if (link_bw)
 		drm_dbg_kms(&i915->drm,
 			    "Using LINK_BW_SET value %02x\n", link_bw);
 	else
 		drm_dbg_kms(&i915->drm,
 			    "Using LINK_RATE_SET value %02x\n", rate_select);

 	/* Write the link configuration data */
 	link_config[0] = link_bw;
 	link_config[1] = intel_dp->lane_count;
 	if (drm_dp_enhanced_frame_cap(intel_dp->dpcd))
 		link_config[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
 	drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_BW_SET, link_config, 2);

 	/* eDP 1.4 rate select method. */
 	if (!link_bw)
 		drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_RATE_SET,
 				  &rate_select, 1);

 	link_config[0] = 0;
 	link_config[1] = DP_SET_ANSI_8B10B;
 	drm_dp_dpcd_write(&intel_dp->aux, DP_DOWNSPREAD_CTRL, link_config, 2);

 	intel_dp->DP |= DP_PORT_EN;

 	/* clock recovery */
 	if (!intel_dp_reset_link_train(intel_dp,
 				       DP_TRAINING_PATTERN_1 |
 				       DP_LINK_SCRAMBLING_DISABLE)) {
 		drm_err(&i915->drm, "failed to enable link training\n");
 		return false;
 	}

 	/*
 	 * The DP 1.4 spec defines the max clock recovery retries value
 	 * as 10 but for pre-DP 1.4 devices we set a very tolerant
 	 * retry limit of 80 (4 voltage levels x 4 preemphasis levels x
 	 * x 5 identical voltage retries). Since the previous specs didn't
 	 * define a limit and created the possibility of an infinite loop
 	 * we want to prevent any sync from triggering that corner case.
 	 */
 	if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
 		max_cr_tries = 10;
 	else
 		max_cr_tries = 80;

 	voltage_tries = 1;
 	for (cr_tries = 0; cr_tries < max_cr_tries; ++cr_tries) {
 		u8 link_status[DP_LINK_STATUS_SIZE];

 		drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd);

 		if (!intel_dp_get_link_status(intel_dp, link_status)) {
 			drm_err(&i915->drm, "failed to get link status\n");
 			return false;
 		}

 		if (drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count)) {
 			drm_dbg_kms(&i915->drm, "clock recovery OK\n");
 			return true;
 		}

 		if (voltage_tries == 5) {
 			drm_dbg_kms(&i915->drm,
 				    "Same voltage tried 5 times\n");
 			return false;
 		}

 		if (max_vswing_reached) {
 			drm_dbg_kms(&i915->drm, "Max Voltage Swing reached\n");
 			return false;
 		}

 		voltage = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;

 		/* Update training set as requested by target */
 		intel_dp_get_adjust_train(intel_dp, link_status);
 		if (!intel_dp_update_link_train(intel_dp)) {
 			drm_err(&i915->drm,
 				"failed to update link training\n");
 			return false;
 		}

 		if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) ==
 		    voltage)
 			++voltage_tries;
 		else
 			voltage_tries = 1;

 		if (intel_dp_link_max_vswing_reached(intel_dp))
 			max_vswing_reached = true;

 	}
 	drm_err(&i915->drm,
 		"Failed clock recovery %d times, giving up!\n", max_cr_tries);
 	return false;
 }

 /*
  * Pick training pattern for channel equalization. Training pattern 4 for HBR3
  * or for 1.4 devices that support it, training Pattern 3 for HBR2
  * or 1.2 devices that support it, Training Pattern 2 otherwise.
  */
 static u32 intel_dp_training_pattern(struct intel_dp *intel_dp)
 {
 	bool source_tps3, sink_tps3, source_tps4, sink_tps4;

 	/*
 	 * Intel platforms that support HBR3 also support TPS4. It is mandatory
 	 * for all downstream devices that support HBR3. There are no known eDP
 	 * panels that support TPS4 as of Feb 2018 as per VESA eDP_v1.4b_E1
 	 * specification.
 	 */
 	source_tps4 = intel_dp_source_supports_hbr3(intel_dp);
 	sink_tps4 = drm_dp_tps4_supported(intel_dp->dpcd);
 	if (source_tps4 && sink_tps4) {
 		return DP_TRAINING_PATTERN_4;
 	} else if (intel_dp->link_rate == 810000) {
 		if (!source_tps4)
 			drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 				    "8.1 Gbps link rate without source HBR3/TPS4 support\n");
 		if (!sink_tps4)
 			drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 				    "8.1 Gbps link rate without sink TPS4 support\n");
 	}
 	/*
 	 * Intel platforms that support HBR2 also support TPS3. TPS3 support is
 	 * also mandatory for downstream devices that support HBR2. However, not
 	 * all sinks follow the spec.
 	 */
 	source_tps3 = intel_dp_source_supports_hbr2(intel_dp);
 	sink_tps3 = drm_dp_tps3_supported(intel_dp->dpcd);
 	if (source_tps3 && sink_tps3) {
 		return  DP_TRAINING_PATTERN_3;
 	} else if (intel_dp->link_rate >= 540000) {
 		if (!source_tps3)
 			drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 				    ">=5.4/6.48 Gbps link rate without source HBR2/TPS3 support\n");
 		if (!sink_tps3)
 			drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 				    ">=5.4/6.48 Gbps link rate without sink TPS3 support\n");
 	}

 	return DP_TRAINING_PATTERN_2;
 }

 static bool
 intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
 {
 	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
 	int tries;
 	u32 training_pattern;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 	bool channel_eq = false;

 	training_pattern = intel_dp_training_pattern(intel_dp);
 	/* Scrambling is disabled for TPS2/3 and enabled for TPS4 */
 	if (training_pattern != DP_TRAINING_PATTERN_4)
 		training_pattern |= DP_LINK_SCRAMBLING_DISABLE;

 	/* channel equalization */
 	if (!intel_dp_set_link_train(intel_dp,
 				     training_pattern)) {
 		drm_err(&i915->drm, "failed to start channel equalization\n");
 		return false;
 	}

 	for (tries = 0; tries < 5; tries++) {

 		drm_dp_link_train_channel_eq_delay(intel_dp->dpcd);
 		if (!intel_dp_get_link_status(intel_dp, link_status)) {
 			drm_err(&i915->drm,
 				"failed to get link status\n");
 			break;
 		}

 		/* Make sure clock is still ok */
 		if (!drm_dp_clock_recovery_ok(link_status,
 					      intel_dp->lane_count)) {
 			intel_dp_dump_link_status(link_status);
 			drm_dbg_kms(&i915->drm,
 				    "Clock recovery check failed, cannot "
 				    "continue channel equalization\n");
 			break;
 		}

 		if (drm_dp_channel_eq_ok(link_status,
 					 intel_dp->lane_count)) {
 			channel_eq = true;
 			drm_dbg_kms(&i915->drm, "Channel EQ done. DP Training "
 				    "successful\n");
 			break;
 		}

 		/* Update training set as requested by target */
 		intel_dp_get_adjust_train(intel_dp, link_status);
 		if (!intel_dp_update_link_train(intel_dp)) {
 			drm_err(&i915->drm,
 				"failed to update link training\n");
 			break;
 		}
 	}

 	/* Try 5 times, else fail and try at lower BW */
 	if (tries == 5) {
 		intel_dp_dump_link_status(link_status);
 		drm_dbg_kms(&i915->drm,
 			    "Channel equalization failed 5 times\n");
 	}

 	intel_dp_set_idle_link_train(intel_dp);

 	return channel_eq;

 }

 void intel_dp_stop_link_train(struct intel_dp *intel_dp)
 {
 	intel_dp->link_trained = true;

 	intel_dp_set_link_train(intel_dp,
 				DP_TRAINING_PATTERN_DISABLE);
 }

 void
 intel_dp_start_link_train(struct intel_dp *intel_dp)
 {
 	struct intel_connector *intel_connector = intel_dp->attached_connector;

 	if (!intel_dp_link_training_clock_recovery(intel_dp))
 		goto failure_handling;
 	if (!intel_dp_link_training_channel_equalization(intel_dp))
 		goto failure_handling;

 	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 		    "[CONNECTOR:%d:%s] Link Training Passed at Link Rate = %d, Lane count = %d",
 		    intel_connector->base.base.id,
 		    intel_connector->base.name,
 		    intel_dp->link_rate, intel_dp->lane_count);
 	return;

  failure_handling:
 	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 		    "[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
 		    intel_connector->base.base.id,
 		    intel_connector->base.name,
 		    intel_dp->link_rate, intel_dp->lane_count);

 	if (intel_dp->hobl_active) {
 		drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
 			    "Link Training failed with HOBL active, not enabling it from now on");
 		intel_dp->hobl_failed = true;
 	} else if (intel_dp_get_link_train_fallback_values(intel_dp,
 							   intel_dp->link_rate,
 							   intel_dp->lane_count)) {
 		return;
 	}

 	/* Schedule a Hotplug Uevent to userspace to start modeset */
 	schedule_work(&intel_connector->modeset_retry_work);
 }
	/*
	* Copyright © 2008-2015 Intel Corporation
	*
	* Permission is hereby granted, free of charge, to any person obtaining a
	* copy of this software and associated documentation files (the "Software"),
	* to deal in the Software without restriction, including without limitation
	* the rights to use, copy, modify, merge, publish, distribute, sublicense,
	* and/or sell copies of the Software, and to permit persons to whom the
	* Software is furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice (including the next
	* paragraph) shall be included in all copies or substantial portions of the
	* Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
	* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
	* IN THE SOFTWARE.
	*/

	#include "intel_display_types.h"
	#include "intel_dp.h"
	#include "intel_dp_link_training.h"

	static void
	intel_dp_dump_link_status(const u8 link_status[DP_LINK_STATUS_SIZE])
	{

	DRM_DEBUG_KMS("ln0_1:0x%x ln2_3:0x%x align:0x%x sink:0x%x adj_req0_1:0x%x adj_req2_3:0x%x",
	link_status[0], link_status[1], link_status[2],
	link_status[3], link_status[4], link_status[5]);
	}

	static u8 dp_voltage_max(u8 preemph)
	{
	switch (preemph & DP_TRAIN_PRE_EMPHASIS_MASK) {
	case DP_TRAIN_PRE_EMPH_LEVEL_0:
	return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
	case DP_TRAIN_PRE_EMPH_LEVEL_1:
	return DP_TRAIN_VOLTAGE_SWING_LEVEL_2;
	case DP_TRAIN_PRE_EMPH_LEVEL_2:
	return DP_TRAIN_VOLTAGE_SWING_LEVEL_1;
	case DP_TRAIN_PRE_EMPH_LEVEL_3:
	default:
	return DP_TRAIN_VOLTAGE_SWING_LEVEL_0;
	}
	}

	void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
	const u8 link_status[DP_LINK_STATUS_SIZE])
	{
	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
	u8 v = 0;
	u8 p = 0;
	int lane;
	u8 voltage_max;
	u8 preemph_max;

	for (lane = 0; lane < intel_dp->lane_count; lane++) {
	v = max(v, drm_dp_get_adjust_request_voltage(link_status, lane));
	p = max(p, drm_dp_get_adjust_request_pre_emphasis(link_status, lane));
	}

	preemph_max = intel_dp->preemph_max(intel_dp);
	drm_WARN_ON_ONCE(&i915->drm,
	preemph_max != DP_TRAIN_PRE_EMPH_LEVEL_2 &&
	preemph_max != DP_TRAIN_PRE_EMPH_LEVEL_3);

	if (p >= preemph_max)
	p = preemph_max \| DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;

	v = min(v, dp_voltage_max(p));

	voltage_max = intel_dp->voltage_max(intel_dp);
	drm_WARN_ON_ONCE(&i915->drm,
	voltage_max != DP_TRAIN_VOLTAGE_SWING_LEVEL_2 &&
	voltage_max != DP_TRAIN_VOLTAGE_SWING_LEVEL_3);

	if (v >= voltage_max)
	v = voltage_max \| DP_TRAIN_MAX_SWING_REACHED;

	for (lane = 0; lane < 4; lane++)
	intel_dp->train_set[lane] = v \| p;
	}

	static bool
	intel_dp_set_link_train(struct intel_dp *intel_dp,
	u8 dp_train_pat)
	{
	u8 buf[sizeof(intel_dp->train_set) + 1];
	int ret, len;

	intel_dp_program_link_training_pattern(intel_dp, dp_train_pat);

	buf[0] = dp_train_pat;
	if ((dp_train_pat & DP_TRAINING_PATTERN_MASK) ==
	DP_TRAINING_PATTERN_DISABLE) {
	/* don't write DP_TRAINING_LANEx_SET on disable */
	len = 1;
	} else {
	/* DP_TRAINING_LANEx_SET follow DP_TRAINING_PATTERN_SET */
	memcpy(buf + 1, intel_dp->train_set, intel_dp->lane_count);
	len = intel_dp->lane_count + 1;
	}

	ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_PATTERN_SET,
	buf, len);

	return ret == len;
	}

	static bool
	intel_dp_reset_link_train(struct intel_dp *intel_dp,
	u8 dp_train_pat)
	{
	memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
	intel_dp_set_signal_levels(intel_dp);
	return intel_dp_set_link_train(intel_dp, dp_train_pat);
	}

	static bool
	intel_dp_update_link_train(struct intel_dp *intel_dp)
	{
	int ret;

	intel_dp_set_signal_levels(intel_dp);

	ret = drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_LANE0_SET,
	intel_dp->train_set, intel_dp->lane_count);

	return ret == intel_dp->lane_count;
	}

	static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp)
	{
	int lane;

	for (lane = 0; lane < intel_dp->lane_count; lane++)
	if ((intel_dp->train_set[lane] &
	DP_TRAIN_MAX_SWING_REACHED) == 0)
	return false;

	return true;
	}

	/* Enable corresponding port and start training pattern 1 */
	static bool
	intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp)
	{
	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
	u8 voltage;
	int voltage_tries, cr_tries, max_cr_tries;
	bool max_vswing_reached = false;
	u8 link_config[2];
	u8 link_bw, rate_select;

	if (intel_dp->prepare_link_retrain)
	intel_dp->prepare_link_retrain(intel_dp);

	intel_dp_compute_rate(intel_dp, intel_dp->link_rate,
	&link_bw, &rate_select);

	if (link_bw)
	drm_dbg_kms(&i915->drm,
	"Using LINK_BW_SET value %02x\n", link_bw);
	else
	drm_dbg_kms(&i915->drm,
	"Using LINK_RATE_SET value %02x\n", rate_select);

	/* Write the link configuration data */
	link_config[0] = link_bw;
	link_config[1] = intel_dp->lane_count;
	if (drm_dp_enhanced_frame_cap(intel_dp->dpcd))
	link_config[1] \|= DP_LANE_COUNT_ENHANCED_FRAME_EN;
	drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_BW_SET, link_config, 2);

	/* eDP 1.4 rate select method. */
	if (!link_bw)
	drm_dp_dpcd_write(&intel_dp->aux, DP_LINK_RATE_SET,
	&rate_select, 1);

	link_config[0] = 0;
	link_config[1] = DP_SET_ANSI_8B10B;
	drm_dp_dpcd_write(&intel_dp->aux, DP_DOWNSPREAD_CTRL, link_config, 2);

	intel_dp->DP \|= DP_PORT_EN;

	/* clock recovery */
	if (!intel_dp_reset_link_train(intel_dp,
	DP_TRAINING_PATTERN_1 \|
	DP_LINK_SCRAMBLING_DISABLE)) {
	drm_err(&i915->drm, "failed to enable link training\n");
	return false;
	}

	/*
	* The DP 1.4 spec defines the max clock recovery retries value
	* as 10 but for pre-DP 1.4 devices we set a very tolerant
	* retry limit of 80 (4 voltage levels x 4 preemphasis levels x
	* x 5 identical voltage retries). Since the previous specs didn't
	* define a limit and created the possibility of an infinite loop
	* we want to prevent any sync from triggering that corner case.
	*/
	if (intel_dp->dpcd[DP_DPCD_REV] >= DP_DPCD_REV_14)
	max_cr_tries = 10;
	else
	max_cr_tries = 80;

	voltage_tries = 1;
	for (cr_tries = 0; cr_tries < max_cr_tries; ++cr_tries) {
	u8 link_status[DP_LINK_STATUS_SIZE];

	drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd);

	if (!intel_dp_get_link_status(intel_dp, link_status)) {
	drm_err(&i915->drm, "failed to get link status\n");
	return false;
	}

	if (drm_dp_clock_recovery_ok(link_status, intel_dp->lane_count)) {
	drm_dbg_kms(&i915->drm, "clock recovery OK\n");
	return true;
	}

	if (voltage_tries == 5) {
	drm_dbg_kms(&i915->drm,
	"Same voltage tried 5 times\n");
	return false;
	}

	if (max_vswing_reached) {
	drm_dbg_kms(&i915->drm, "Max Voltage Swing reached\n");
	return false;
	}

	voltage = intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK;

	/* Update training set as requested by target */
	intel_dp_get_adjust_train(intel_dp, link_status);
	if (!intel_dp_update_link_train(intel_dp)) {
	drm_err(&i915->drm,
	"failed to update link training\n");
	return false;
	}

	if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) ==
	voltage)
	++voltage_tries;
	else
	voltage_tries = 1;

	if (intel_dp_link_max_vswing_reached(intel_dp))
	max_vswing_reached = true;

	}
	drm_err(&i915->drm,
	"Failed clock recovery %d times, giving up!\n", max_cr_tries);
	return false;
	}

	/*
	* Pick training pattern for channel equalization. Training pattern 4 for HBR3
	* or for 1.4 devices that support it, training Pattern 3 for HBR2
	* or 1.2 devices that support it, Training Pattern 2 otherwise.
	*/
	static u32 intel_dp_training_pattern(struct intel_dp *intel_dp)
	{
	bool source_tps3, sink_tps3, source_tps4, sink_tps4;

	/*
	* Intel platforms that support HBR3 also support TPS4. It is mandatory
	* for all downstream devices that support HBR3. There are no known eDP
	* panels that support TPS4 as of Feb 2018 as per VESA eDP_v1.4b_E1
	* specification.
	*/
	source_tps4 = intel_dp_source_supports_hbr3(intel_dp);
	sink_tps4 = drm_dp_tps4_supported(intel_dp->dpcd);
	if (source_tps4 && sink_tps4) {
	return DP_TRAINING_PATTERN_4;
	} else if (intel_dp->link_rate == 810000) {
	if (!source_tps4)
	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	"8.1 Gbps link rate without source HBR3/TPS4 support\n");
	if (!sink_tps4)
	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	"8.1 Gbps link rate without sink TPS4 support\n");
	}
	/*
	* Intel platforms that support HBR2 also support TPS3. TPS3 support is
	* also mandatory for downstream devices that support HBR2. However, not
	* all sinks follow the spec.
	*/
	source_tps3 = intel_dp_source_supports_hbr2(intel_dp);
	sink_tps3 = drm_dp_tps3_supported(intel_dp->dpcd);
	if (source_tps3 && sink_tps3) {
	return DP_TRAINING_PATTERN_3;
	} else if (intel_dp->link_rate >= 540000) {
	if (!source_tps3)
	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	">=5.4/6.48 Gbps link rate without source HBR2/TPS3 support\n");
	if (!sink_tps3)
	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	">=5.4/6.48 Gbps link rate without sink TPS3 support\n");
	}

	return DP_TRAINING_PATTERN_2;
	}

	static bool
	intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp)
	{
	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
	int tries;
	u32 training_pattern;
	u8 link_status[DP_LINK_STATUS_SIZE];
	bool channel_eq = false;

	training_pattern = intel_dp_training_pattern(intel_dp);
	/* Scrambling is disabled for TPS2/3 and enabled for TPS4 */
	if (training_pattern != DP_TRAINING_PATTERN_4)
	training_pattern \|= DP_LINK_SCRAMBLING_DISABLE;

	/* channel equalization */
	if (!intel_dp_set_link_train(intel_dp,
	training_pattern)) {
	drm_err(&i915->drm, "failed to start channel equalization\n");
	return false;
	}

	for (tries = 0; tries < 5; tries++) {

	drm_dp_link_train_channel_eq_delay(intel_dp->dpcd);
	if (!intel_dp_get_link_status(intel_dp, link_status)) {
	drm_err(&i915->drm,
	"failed to get link status\n");
	break;
	}

	/* Make sure clock is still ok */
	if (!drm_dp_clock_recovery_ok(link_status,
	intel_dp->lane_count)) {
	intel_dp_dump_link_status(link_status);
	drm_dbg_kms(&i915->drm,
	"Clock recovery check failed, cannot "
	"continue channel equalization\n");
	break;
	}

	if (drm_dp_channel_eq_ok(link_status,
	intel_dp->lane_count)) {
	channel_eq = true;
	drm_dbg_kms(&i915->drm, "Channel EQ done. DP Training "
	"successful\n");
	break;
	}

	/* Update training set as requested by target */
	intel_dp_get_adjust_train(intel_dp, link_status);
	if (!intel_dp_update_link_train(intel_dp)) {
	drm_err(&i915->drm,
	"failed to update link training\n");
	break;
	}
	}

	/* Try 5 times, else fail and try at lower BW */
	if (tries == 5) {
	intel_dp_dump_link_status(link_status);
	drm_dbg_kms(&i915->drm,
	"Channel equalization failed 5 times\n");
	}

	intel_dp_set_idle_link_train(intel_dp);

	return channel_eq;

	}

	void intel_dp_stop_link_train(struct intel_dp *intel_dp)
	{
	intel_dp->link_trained = true;

	intel_dp_set_link_train(intel_dp,
	DP_TRAINING_PATTERN_DISABLE);
	}

	void
	intel_dp_start_link_train(struct intel_dp *intel_dp)
	{
	struct intel_connector *intel_connector = intel_dp->attached_connector;

	if (!intel_dp_link_training_clock_recovery(intel_dp))
	goto failure_handling;
	if (!intel_dp_link_training_channel_equalization(intel_dp))
	goto failure_handling;

	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	"[CONNECTOR:%d:%s] Link Training Passed at Link Rate = %d, Lane count = %d",
	intel_connector->base.base.id,
	intel_connector->base.name,
	intel_dp->link_rate, intel_dp->lane_count);
	return;

	failure_handling:
	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	"[CONNECTOR:%d:%s] Link Training failed at link rate = %d, lane count = %d",
	intel_connector->base.base.id,
	intel_connector->base.name,
	intel_dp->link_rate, intel_dp->lane_count);

	if (intel_dp->hobl_active) {
	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
	"Link Training failed with HOBL active, not enabling it from now on");
	intel_dp->hobl_failed = true;
	} else if (intel_dp_get_link_train_fallback_values(intel_dp,
	intel_dp->link_rate,
	intel_dp->lane_count)) {
	return;
	}

	/* Schedule a Hotplug Uevent to userspace to start modeset */
	schedule_work(&intel_connector->modeset_retry_work);
	}