1 files changed, 885 insertions, 0 deletions

diff --git a/drivers/gpu/drm/tegra/dp.c b/drivers/gpu/drm/tegra/dp.c
new file mode 100644
index 000000000..08fbd8f15
--- /dev/null
+++ b/drivers/gpu/drm/tegra/dp.c
@@ -0,0 +1,885 @@
+// SPDX-License-Identifier: MIT
+/*
+ * Copyright (C) 2013-2019 NVIDIA Corporation
+ * Copyright (C) 2015 Rob Clark
+ */
+
+#include <drm/display/drm_dp_helper.h>
+#include <drm/drm_crtc.h>
+#include <drm/drm_print.h>
+
+#include "dp.h"
+
+static const u8 drm_dp_edp_revisions[] = { 0x11, 0x12, 0x13, 0x14 };
+
+static void drm_dp_link_caps_reset(struct drm_dp_link_caps *caps)
+{
+	caps->enhanced_framing = false;
+	caps->tps3_supported = false;
+	caps->fast_training = false;
+	caps->channel_coding = false;
+	caps->alternate_scrambler_reset = false;
+}
+
+void drm_dp_link_caps_copy(struct drm_dp_link_caps *dest,
+			   const struct drm_dp_link_caps *src)
+{
+	dest->enhanced_framing = src->enhanced_framing;
+	dest->tps3_supported = src->tps3_supported;
+	dest->fast_training = src->fast_training;
+	dest->channel_coding = src->channel_coding;
+	dest->alternate_scrambler_reset = src->alternate_scrambler_reset;
+}
+
+static void drm_dp_link_reset(struct drm_dp_link *link)
+{
+	unsigned int i;
+
+	if (!link)
+		return;
+
+	link->revision = 0;
+	link->max_rate = 0;
+	link->max_lanes = 0;
+
+	drm_dp_link_caps_reset(&link->caps);
+	link->aux_rd_interval.cr = 0;
+	link->aux_rd_interval.ce = 0;
+	link->edp = 0;
+
+	link->rate = 0;
+	link->lanes = 0;
+
+	for (i = 0; i < DP_MAX_SUPPORTED_RATES; i++)
+		link->rates[i] = 0;
+
+	link->num_rates = 0;
+}
+
+/**
+ * drm_dp_link_add_rate() - add a rate to the list of supported rates
+ * @link: the link to add the rate to
+ * @rate: the rate to add
+ *
+ * Add a link rate to the list of supported link rates.
+ *
+ * Returns:
+ * 0 on success or one of the following negative error codes on failure:
+ * - ENOSPC if the maximum number of supported rates has been reached
+ * - EEXISTS if the link already supports this rate
+ *
+ * See also:
+ * drm_dp_link_remove_rate()
+ */
+int drm_dp_link_add_rate(struct drm_dp_link *link, unsigned long rate)
+{
+	unsigned int i, pivot;
+
+	if (link->num_rates == DP_MAX_SUPPORTED_RATES)
+		return -ENOSPC;
+
+	for (pivot = 0; pivot < link->num_rates; pivot++)
+		if (rate <= link->rates[pivot])
+			break;
+
+	if (pivot != link->num_rates && rate == link->rates[pivot])
+		return -EEXIST;
+
+	for (i = link->num_rates; i > pivot; i--)
+		link->rates[i] = link->rates[i - 1];
+
+	link->rates[pivot] = rate;
+	link->num_rates++;
+
+	return 0;
+}
+
+/**
+ * drm_dp_link_remove_rate() - remove a rate from the list of supported rates
+ * @link: the link from which to remove the rate
+ * @rate: the rate to remove
+ *
+ * Removes a link rate from the list of supported link rates.
+ *
+ * Returns:
+ * 0 on success or one of the following negative error codes on failure:
+ * - EINVAL if the specified rate is not among the supported rates
+ *
+ * See also:
+ * drm_dp_link_add_rate()
+ */
+int drm_dp_link_remove_rate(struct drm_dp_link *link, unsigned long rate)
+{
+	unsigned int i;
+
+	for (i = 0; i < link->num_rates; i++)
+		if (rate == link->rates[i])
+			break;
+
+	if (i == link->num_rates)
+		return -EINVAL;
+
+	link->num_rates--;
+
+	while (i < link->num_rates) {
+		link->rates[i] = link->rates[i + 1];
+		i++;
+	}
+
+	return 0;
+}
+
+/**
+ * drm_dp_link_update_rates() - normalize the supported link rates array
+ * @link: the link for which to normalize the supported link rates
+ *
+ * Users should call this function after they've manually modified the array
+ * of supported link rates. This function removes any stale entries, compacts
+ * the array and updates the supported link rate count. Note that calling the
+ * drm_dp_link_remove_rate() function already does this janitorial work.
+ *
+ * See also:
+ * drm_dp_link_add_rate(), drm_dp_link_remove_rate()
+ */
+void drm_dp_link_update_rates(struct drm_dp_link *link)
+{
+	unsigned int i, count = 0;
+
+	for (i = 0; i < link->num_rates; i++) {
+		if (link->rates[i] != 0)
+			link->rates[count++] = link->rates[i];
+	}
+
+	for (i = count; i < link->num_rates; i++)
+		link->rates[i] = 0;
+
+	link->num_rates = count;
+}
+
+/**
+ * drm_dp_link_probe() - probe a DisplayPort link for capabilities
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to structure in which to return link capabilities
+ *
+ * The structure filled in by this function can usually be passed directly
+ * into drm_dp_link_power_up() and drm_dp_link_configure() to power up and
+ * configure the link based on the link's capabilities.
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+	u8 dpcd[DP_RECEIVER_CAP_SIZE], value;
+	unsigned int rd_interval;
+	int err;
+
+	drm_dp_link_reset(link);
+
+	err = drm_dp_dpcd_read(aux, DP_DPCD_REV, dpcd, sizeof(dpcd));
+	if (err < 0)
+		return err;
+
+	link->revision = dpcd[DP_DPCD_REV];
+	link->max_rate = drm_dp_max_link_rate(dpcd);
+	link->max_lanes = drm_dp_max_lane_count(dpcd);
+
+	link->caps.enhanced_framing = drm_dp_enhanced_frame_cap(dpcd);
+	link->caps.tps3_supported = drm_dp_tps3_supported(dpcd);
+	link->caps.fast_training = drm_dp_fast_training_cap(dpcd);
+	link->caps.channel_coding = drm_dp_channel_coding_supported(dpcd);
+
+	if (drm_dp_alternate_scrambler_reset_cap(dpcd)) {
+		link->caps.alternate_scrambler_reset = true;
+
+		err = drm_dp_dpcd_readb(aux, DP_EDP_DPCD_REV, &value);
+		if (err < 0)
+			return err;
+
+		if (value >= ARRAY_SIZE(drm_dp_edp_revisions))
+			DRM_ERROR("unsupported eDP version: %02x\n", value);
+		else
+			link->edp = drm_dp_edp_revisions[value];
+	}
+
+	/*
+	 * The DPCD stores the AUX read interval in units of 4 ms. There are
+	 * two special cases:
+	 *
+	 *   1) if the TRAINING_AUX_RD_INTERVAL field is 0, the clock recovery
+	 *      and channel equalization should use 100 us or 400 us AUX read
+	 *      intervals, respectively
+	 *
+	 *   2) for DP v1.4 and above, clock recovery should always use 100 us
+	 *      AUX read intervals
+	 */
+	rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &
+			   DP_TRAINING_AUX_RD_MASK;
+
+	if (rd_interval > 4) {
+		DRM_DEBUG_KMS("AUX interval %u out of range (max. 4)\n",
+			      rd_interval);
+		rd_interval = 4;
+	}
+
+	rd_interval *= 4 * USEC_PER_MSEC;
+
+	if (rd_interval == 0 || link->revision >= DP_DPCD_REV_14)
+		link->aux_rd_interval.cr = 100;
+
+	if (rd_interval == 0)
+		link->aux_rd_interval.ce = 400;
+
+	link->rate = link->max_rate;
+	link->lanes = link->max_lanes;
+
+	/* Parse SUPPORTED_LINK_RATES from eDP 1.4 */
+	if (link->edp >= 0x14) {
+		u8 supported_rates[DP_MAX_SUPPORTED_RATES * 2];
+		unsigned int i;
+		u16 rate;
+
+		err = drm_dp_dpcd_read(aux, DP_SUPPORTED_LINK_RATES,
+				       supported_rates,
+				       sizeof(supported_rates));
+		if (err < 0)
+			return err;
+
+		for (i = 0; i < DP_MAX_SUPPORTED_RATES; i++) {
+			rate = supported_rates[i * 2 + 1] << 8 |
+			       supported_rates[i * 2 + 0];
+
+			drm_dp_link_add_rate(link, rate * 200);
+		}
+	}
+
+	return 0;
+}
+
+/**
+ * drm_dp_link_power_up() - power up a DisplayPort link
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to a structure containing the link configuration
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+	u8 value;
+	int err;
+
+	/* DP_SET_POWER register is only available on DPCD v1.1 and later */
+	if (link->revision < 0x11)
+		return 0;
+
+	err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
+	if (err < 0)
+		return err;
+
+	value &= ~DP_SET_POWER_MASK;
+	value |= DP_SET_POWER_D0;
+
+	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+	if (err < 0)
+		return err;
+
+	/*
+	 * According to the DP 1.1 specification, a "Sink Device must exit the
+	 * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink
+	 * Control Field" (register 0x600).
+	 */
+	usleep_range(1000, 2000);
+
+	return 0;
+}
+
+/**
+ * drm_dp_link_power_down() - power down a DisplayPort link
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to a structure containing the link configuration
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_power_down(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+	u8 value;
+	int err;
+
+	/* DP_SET_POWER register is only available on DPCD v1.1 and later */
+	if (link->revision < 0x11)
+		return 0;
+
+	err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
+	if (err < 0)
+		return err;
+
+	value &= ~DP_SET_POWER_MASK;
+	value |= DP_SET_POWER_D3;
+
+	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+/**
+ * drm_dp_link_configure() - configure a DisplayPort link
+ * @aux: DisplayPort AUX channel
+ * @link: pointer to a structure containing the link configuration
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
+{
+	u8 values[2], value;
+	int err;
+
+	if (link->ops && link->ops->configure) {
+		err = link->ops->configure(link);
+		if (err < 0) {
+			DRM_ERROR("failed to configure DP link: %d\n", err);
+			return err;
+		}
+	}
+
+	values[0] = drm_dp_link_rate_to_bw_code(link->rate);
+	values[1] = link->lanes;
+
+	if (link->caps.enhanced_framing)
+		values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;
+
+	err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values));
+	if (err < 0)
+		return err;
+
+	if (link->caps.channel_coding)
+		value = DP_SET_ANSI_8B10B;
+	else
+		value = 0;
+
+	err = drm_dp_dpcd_writeb(aux, DP_MAIN_LINK_CHANNEL_CODING_SET, value);
+	if (err < 0)
+		return err;
+
+	if (link->caps.alternate_scrambler_reset) {
+		err = drm_dp_dpcd_writeb(aux, DP_EDP_CONFIGURATION_SET,
+					 DP_ALTERNATE_SCRAMBLER_RESET_ENABLE);
+		if (err < 0)
+			return err;
+	}
+
+	return 0;
+}
+
+/**
+ * drm_dp_link_choose() - choose the lowest possible configuration for a mode
+ * @link: DRM DP link object
+ * @mode: DRM display mode
+ * @info: DRM display information
+ *
+ * According to the eDP specification, a source should select a configuration
+ * with the lowest number of lanes and the lowest possible link rate that can
+ * match the bitrate requirements of a video mode. However it must ensure not
+ * to exceed the capabilities of the sink.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_choose(struct drm_dp_link *link,
+		       const struct drm_display_mode *mode,
+		       const struct drm_display_info *info)
+{
+	/* available link symbol clock rates */
+	static const unsigned int rates[3] = { 162000, 270000, 540000 };
+	/* available number of lanes */
+	static const unsigned int lanes[3] = { 1, 2, 4 };
+	unsigned long requirement, capacity;
+	unsigned int rate = link->max_rate;
+	unsigned int i, j;
+
+	/* bandwidth requirement */
+	requirement = mode->clock * info->bpc * 3;
+
+	for (i = 0; i < ARRAY_SIZE(lanes) && lanes[i] <= link->max_lanes; i++) {
+		for (j = 0; j < ARRAY_SIZE(rates) && rates[j] <= rate; j++) {
+			/*
+			 * Capacity for this combination of lanes and rate,
+			 * factoring in the ANSI 8B/10B encoding.
+			 *
+			 * Link rates in the DRM DP helpers are really link
+			 * symbol frequencies, so a tenth of the actual rate
+			 * of the link.
+			 */
+			capacity = lanes[i] * (rates[j] * 10) * 8 / 10;
+
+			if (capacity >= requirement) {
+				DRM_DEBUG_KMS("using %u lanes at %u kHz (%lu/%lu kbps)\n",
+					      lanes[i], rates[j], requirement,
+					      capacity);
+				link->lanes = lanes[i];
+				link->rate = rates[j];
+				return 0;
+			}
+		}
+	}
+
+	return -ERANGE;
+}
+
+/**
+ * DOC: Link training
+ *
+ * These functions contain common logic and helpers to implement DisplayPort
+ * link training.
+ */
+
+/**
+ * drm_dp_link_train_init() - initialize DisplayPort link training state
+ * @train: DisplayPort link training state
+ */
+void drm_dp_link_train_init(struct drm_dp_link_train *train)
+{
+	struct drm_dp_link_train_set *request = &train->request;
+	struct drm_dp_link_train_set *adjust = &train->adjust;
+	unsigned int i;
+
+	for (i = 0; i < 4; i++) {
+		request->voltage_swing[i] = 0;
+		adjust->voltage_swing[i] = 0;
+
+		request->pre_emphasis[i] = 0;
+		adjust->pre_emphasis[i] = 0;
+
+		request->post_cursor[i] = 0;
+		adjust->post_cursor[i] = 0;
+	}
+
+	train->pattern = DP_TRAINING_PATTERN_DISABLE;
+	train->clock_recovered = false;
+	train->channel_equalized = false;
+}
+
+static bool drm_dp_link_train_valid(const struct drm_dp_link_train *train)
+{
+	return train->clock_recovered && train->channel_equalized;
+}
+
+static int drm_dp_link_apply_training(struct drm_dp_link *link)
+{
+	struct drm_dp_link_train_set *request = &link->train.request;
+	unsigned int lanes = link->lanes, *vs, *pe, *pc, i;
+	struct drm_dp_aux *aux = link->aux;
+	u8 values[4], pattern = 0;
+	int err;
+
+	err = link->ops->apply_training(link);
+	if (err < 0) {
+		DRM_ERROR("failed to apply link training: %d\n", err);
+		return err;
+	}
+
+	vs = request->voltage_swing;
+	pe = request->pre_emphasis;
+	pc = request->post_cursor;
+
+	/* write currently selected voltage-swing and pre-emphasis levels */
+	for (i = 0; i < lanes; i++)
+		values[i] = DP_TRAIN_VOLTAGE_SWING_LEVEL(vs[i]) |
+			    DP_TRAIN_PRE_EMPHASIS_LEVEL(pe[i]);
+
+	err = drm_dp_dpcd_write(aux, DP_TRAINING_LANE0_SET, values, lanes);
+	if (err < 0) {
+		DRM_ERROR("failed to set training parameters: %d\n", err);
+		return err;
+	}
+
+	/* write currently selected post-cursor level (if supported) */
+	if (link->revision >= 0x12 && link->rate == 540000) {
+		values[0] = values[1] = 0;
+
+		for (i = 0; i < lanes; i++)
+			values[i / 2] |= DP_LANE_POST_CURSOR(i, pc[i]);
+
+		err = drm_dp_dpcd_write(aux, DP_TRAINING_LANE0_1_SET2, values,
+					DIV_ROUND_UP(lanes, 2));
+		if (err < 0) {
+			DRM_ERROR("failed to set post-cursor: %d\n", err);
+			return err;
+		}
+	}
+
+	/* write link pattern */
+	if (link->train.pattern != DP_TRAINING_PATTERN_DISABLE)
+		pattern |= DP_LINK_SCRAMBLING_DISABLE;
+
+	pattern |= link->train.pattern;
+
+	err = drm_dp_dpcd_writeb(aux, DP_TRAINING_PATTERN_SET, pattern);
+	if (err < 0) {
+		DRM_ERROR("failed to set training pattern: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+static void drm_dp_link_train_wait(struct drm_dp_link *link)
+{
+	unsigned long min = 0;
+
+	switch (link->train.pattern) {
+	case DP_TRAINING_PATTERN_1:
+		min = link->aux_rd_interval.cr;
+		break;
+
+	case DP_TRAINING_PATTERN_2:
+	case DP_TRAINING_PATTERN_3:
+		min = link->aux_rd_interval.ce;
+		break;
+
+	default:
+		break;
+	}
+
+	if (min > 0)
+		usleep_range(min, 2 * min);
+}
+
+static void drm_dp_link_get_adjustments(struct drm_dp_link *link,
+					u8 status[DP_LINK_STATUS_SIZE])
+{
+	struct drm_dp_link_train_set *adjust = &link->train.adjust;
+	unsigned int i;
+	u8 post_cursor;
+	int err;
+
+	err = drm_dp_dpcd_read(link->aux, DP_ADJUST_REQUEST_POST_CURSOR2,
+			       &post_cursor, sizeof(post_cursor));
+	if (err < 0) {
+		DRM_ERROR("failed to read post_cursor2: %d\n", err);
+		post_cursor = 0;
+	}
+
+	for (i = 0; i < link->lanes; i++) {
+		adjust->voltage_swing[i] =
+			drm_dp_get_adjust_request_voltage(status, i) >>
+				DP_TRAIN_VOLTAGE_SWING_SHIFT;
+
+		adjust->pre_emphasis[i] =
+			drm_dp_get_adjust_request_pre_emphasis(status, i) >>
+				DP_TRAIN_PRE_EMPHASIS_SHIFT;
+
+		adjust->post_cursor[i] =
+			(post_cursor >> (i << 1)) & 0x3;
+	}
+}
+
+static void drm_dp_link_train_adjust(struct drm_dp_link_train *train)
+{
+	struct drm_dp_link_train_set *request = &train->request;
+	struct drm_dp_link_train_set *adjust = &train->adjust;
+	unsigned int i;
+
+	for (i = 0; i < 4; i++)
+		if (request->voltage_swing[i] != adjust->voltage_swing[i])
+			request->voltage_swing[i] = adjust->voltage_swing[i];
+
+	for (i = 0; i < 4; i++)
+		if (request->pre_emphasis[i] != adjust->pre_emphasis[i])
+			request->pre_emphasis[i] = adjust->pre_emphasis[i];
+
+	for (i = 0; i < 4; i++)
+		if (request->post_cursor[i] != adjust->post_cursor[i])
+			request->post_cursor[i] = adjust->post_cursor[i];
+}
+
+static int drm_dp_link_recover_clock(struct drm_dp_link *link)
+{
+	u8 status[DP_LINK_STATUS_SIZE];
+	int err;
+
+	err = drm_dp_link_apply_training(link);
+	if (err < 0)
+		return err;
+
+	drm_dp_link_train_wait(link);
+
+	err = drm_dp_dpcd_read_link_status(link->aux, status);
+	if (err < 0) {
+		DRM_ERROR("failed to read link status: %d\n", err);
+		return err;
+	}
+
+	if (!drm_dp_clock_recovery_ok(status, link->lanes))
+		drm_dp_link_get_adjustments(link, status);
+	else
+		link->train.clock_recovered = true;
+
+	return 0;
+}
+
+static int drm_dp_link_clock_recovery(struct drm_dp_link *link)
+{
+	unsigned int repeat;
+	int err;
+
+	/* start clock recovery using training pattern 1 */
+	link->train.pattern = DP_TRAINING_PATTERN_1;
+
+	for (repeat = 1; repeat < 5; repeat++) {
+		err = drm_dp_link_recover_clock(link);
+		if (err < 0) {
+			DRM_ERROR("failed to recover clock: %d\n", err);
+			return err;
+		}
+
+		if (link->train.clock_recovered)
+			break;
+
+		drm_dp_link_train_adjust(&link->train);
+	}
+
+	return 0;
+}
+
+static int drm_dp_link_equalize_channel(struct drm_dp_link *link)
+{
+	struct drm_dp_aux *aux = link->aux;
+	u8 status[DP_LINK_STATUS_SIZE];
+	int err;
+
+	err = drm_dp_link_apply_training(link);
+	if (err < 0)
+		return err;
+
+	drm_dp_link_train_wait(link);
+
+	err = drm_dp_dpcd_read_link_status(aux, status);
+	if (err < 0) {
+		DRM_ERROR("failed to read link status: %d\n", err);
+		return err;
+	}
+
+	if (!drm_dp_clock_recovery_ok(status, link->lanes)) {
+		DRM_ERROR("clock recovery lost while equalizing channel\n");
+		link->train.clock_recovered = false;
+		return 0;
+	}
+
+	if (!drm_dp_channel_eq_ok(status, link->lanes))
+		drm_dp_link_get_adjustments(link, status);
+	else
+		link->train.channel_equalized = true;
+
+	return 0;
+}
+
+static int drm_dp_link_channel_equalization(struct drm_dp_link *link)
+{
+	unsigned int repeat;
+	int err;
+
+	/* start channel equalization using pattern 2 or 3 */
+	if (link->caps.tps3_supported)
+		link->train.pattern = DP_TRAINING_PATTERN_3;
+	else
+		link->train.pattern = DP_TRAINING_PATTERN_2;
+
+	for (repeat = 1; repeat < 5; repeat++) {
+		err = drm_dp_link_equalize_channel(link);
+		if (err < 0) {
+			DRM_ERROR("failed to equalize channel: %d\n", err);
+			return err;
+		}
+
+		if (link->train.channel_equalized)
+			break;
+
+		drm_dp_link_train_adjust(&link->train);
+	}
+
+	return 0;
+}
+
+static int drm_dp_link_downgrade(struct drm_dp_link *link)
+{
+	switch (link->rate) {
+	case 162000:
+		return -EINVAL;
+
+	case 270000:
+		link->rate = 162000;
+		break;
+
+	case 540000:
+		link->rate = 270000;
+		return 0;
+	}
+
+	return 0;
+}
+
+static void drm_dp_link_train_disable(struct drm_dp_link *link)
+{
+	int err;
+
+	link->train.pattern = DP_TRAINING_PATTERN_DISABLE;
+
+	err = drm_dp_link_apply_training(link);
+	if (err < 0)
+		DRM_ERROR("failed to disable link training: %d\n", err);
+}
+
+static int drm_dp_link_train_full(struct drm_dp_link *link)
+{
+	int err;
+
+retry:
+	DRM_DEBUG_KMS("full-training link: %u lane%s at %u MHz\n",
+		      link->lanes, (link->lanes > 1) ? "s" : "",
+		      link->rate / 100);
+
+	err = drm_dp_link_configure(link->aux, link);
+	if (err < 0) {
+		DRM_ERROR("failed to configure DP link: %d\n", err);
+		return err;
+	}
+
+	err = drm_dp_link_clock_recovery(link);
+	if (err < 0) {
+		DRM_ERROR("clock recovery failed: %d\n", err);
+		goto out;
+	}
+
+	if (!link->train.clock_recovered) {
+		DRM_ERROR("clock recovery failed, downgrading link\n");
+
+		err = drm_dp_link_downgrade(link);
+		if (err < 0)
+			goto out;
+
+		goto retry;
+	}
+
+	DRM_DEBUG_KMS("clock recovery succeeded\n");
+
+	err = drm_dp_link_channel_equalization(link);
+	if (err < 0) {
+		DRM_ERROR("channel equalization failed: %d\n", err);
+		goto out;
+	}
+
+	if (!link->train.channel_equalized) {
+		DRM_ERROR("channel equalization failed, downgrading link\n");
+
+		err = drm_dp_link_downgrade(link);
+		if (err < 0)
+			goto out;
+
+		goto retry;
+	}
+
+	DRM_DEBUG_KMS("channel equalization succeeded\n");
+
+out:
+	drm_dp_link_train_disable(link);
+	return err;
+}
+
+static int drm_dp_link_train_fast(struct drm_dp_link *link)
+{
+	u8 status[DP_LINK_STATUS_SIZE];
+	int err;
+
+	DRM_DEBUG_KMS("fast-training link: %u lane%s at %u MHz\n",
+		      link->lanes, (link->lanes > 1) ? "s" : "",
+		      link->rate / 100);
+
+	err = drm_dp_link_configure(link->aux, link);
+	if (err < 0) {
+		DRM_ERROR("failed to configure DP link: %d\n", err);
+		return err;
+	}
+
+	/* transmit training pattern 1 for 500 microseconds */
+	link->train.pattern = DP_TRAINING_PATTERN_1;
+
+	err = drm_dp_link_apply_training(link);
+	if (err < 0)
+		goto out;
+
+	usleep_range(500, 1000);
+
+	/* transmit training pattern 2 or 3 for 500 microseconds */
+	if (link->caps.tps3_supported)
+		link->train.pattern = DP_TRAINING_PATTERN_3;
+	else
+		link->train.pattern = DP_TRAINING_PATTERN_2;
+
+	err = drm_dp_link_apply_training(link);
+	if (err < 0)
+		goto out;
+
+	usleep_range(500, 1000);
+
+	err = drm_dp_dpcd_read_link_status(link->aux, status);
+	if (err < 0) {
+		DRM_ERROR("failed to read link status: %d\n", err);
+		goto out;
+	}
+
+	if (!drm_dp_clock_recovery_ok(status, link->lanes)) {
+		DRM_ERROR("clock recovery failed\n");
+		err = -EIO;
+	}
+
+	if (!drm_dp_channel_eq_ok(status, link->lanes)) {
+		DRM_ERROR("channel equalization failed\n");
+		err = -EIO;
+	}
+
+out:
+	drm_dp_link_train_disable(link);
+	return err;
+}
+
+/**
+ * drm_dp_link_train() - perform DisplayPort link training
+ * @link: a DP link object
+ *
+ * Uses the context stored in the DP link object to perform link training. It
+ * is expected that drivers will call drm_dp_link_probe() to obtain the link
+ * capabilities before performing link training.
+ *
+ * If the sink supports fast link training (no AUX CH handshake) and valid
+ * training settings are available, this function will try to perform fast
+ * link training and fall back to full link training on failure.
+ *
+ * Returns: 0 on success or a negative error code on failure.
+ */
+int drm_dp_link_train(struct drm_dp_link *link)
+{
+	int err;
+
+	drm_dp_link_train_init(&link->train);
+
+	if (link->caps.fast_training) {
+		if (drm_dp_link_train_valid(&link->train)) {
+			err = drm_dp_link_train_fast(link);
+			if (err < 0)
+				DRM_ERROR("fast link training failed: %d\n",
+					  err);
+			else
+				return 0;
+		} else {
+			DRM_DEBUG_KMS("training parameters not available\n");
+		}
+	} else {
+		DRM_DEBUG_KMS("fast link training not supported\n");
+	}
+
+	err = drm_dp_link_train_full(link);
+	if (err < 0)
+		DRM_ERROR("full link training failed: %d\n", err);
+
+	return err;
+}