Merge tag 'io_uring-5.11-2021-01-16' of git://git.kernel.dk/linux-block

[linux/fpc-iii.git] / drivers / gpu / drm / i915 / display / intel_dp_link_training.c

/*
 * 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 int intel_dp_lttpr_count(struct intel_dp *intel_dp)
{
        int count = drm_dp_lttpr_count(intel_dp->lttpr_common_caps);

        /*
         * Pretend no LTTPRs in case of LTTPR detection error, or
         * if too many (>8) LTTPRs are detected. This translates to link
         * training in transparent mode.
         */
        return count <= 0 ? 0 : count;
}

static void intel_dp_reset_lttpr_count(struct intel_dp *intel_dp)
{
        intel_dp->lttpr_common_caps[DP_PHY_REPEATER_CNT -
                                    DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV] = 0;
}

static const char *intel_dp_phy_name(enum drm_dp_phy dp_phy,
                                     char *buf, size_t buf_size)
{
        if (dp_phy == DP_PHY_DPRX)
                snprintf(buf, buf_size, "DPRX");
        else
                snprintf(buf, buf_size, "LTTPR %d", dp_phy - DP_PHY_LTTPR1 + 1);

        return buf;
}

static u8 *intel_dp_lttpr_phy_caps(struct intel_dp *intel_dp,
                                   enum drm_dp_phy dp_phy)
{
        return intel_dp->lttpr_phy_caps[dp_phy - DP_PHY_LTTPR1];
}

static void intel_dp_read_lttpr_phy_caps(struct intel_dp *intel_dp,
                                         enum drm_dp_phy dp_phy)
{
        u8 *phy_caps = intel_dp_lttpr_phy_caps(intel_dp, dp_phy);
        char phy_name[10];

        intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name));

        if (drm_dp_read_lttpr_phy_caps(&intel_dp->aux, dp_phy, phy_caps) < 0) {
                drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
                            "failed to read the PHY caps for %s\n",
                            phy_name);
                return;
        }

        drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
                    "%s PHY capabilities: %*ph\n",
                    phy_name,
                    (int)sizeof(intel_dp->lttpr_phy_caps[0]),
                    phy_caps);
}

static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
{
        if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
                                          intel_dp->lttpr_common_caps) < 0) {
                memset(intel_dp->lttpr_common_caps, 0,
                       sizeof(intel_dp->lttpr_common_caps));
                return false;
        }

        drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
                    "LTTPR common capabilities: %*ph\n",
                    (int)sizeof(intel_dp->lttpr_common_caps),
                    intel_dp->lttpr_common_caps);

        return true;
}

static bool
intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable)
{
        u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
                          DP_PHY_REPEATER_MODE_NON_TRANSPARENT;

        return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1;
}

/**
 * intel_dp_lttpr_init - detect LTTPRs and init the LTTPR link training mode
 * @intel_dp: Intel DP struct
 *
 * Read the LTTPR common capabilities, switch to non-transparent link training
 * mode if any is detected and read the PHY capabilities for all detected
 * LTTPRs. In case of an LTTPR detection error or if the number of
 * LTTPRs is more than is supported (8), fall back to the no-LTTPR,
 * transparent mode link training mode.
 *
 * Returns:
 *   >0  if LTTPRs were detected and the non-transparent LT mode was set
 *    0  if no LTTPRs or more than 8 LTTPRs were detected or in case of a
 *       detection failure and the transparent LT mode was set
 */
int intel_dp_lttpr_init(struct intel_dp *intel_dp)
{
        int lttpr_count;
        bool ret;
        int i;

        if (intel_dp_is_edp(intel_dp))
                return 0;

        ret = intel_dp_read_lttpr_common_caps(intel_dp);

        /*
         * See DP Standard v2.0 3.6.6.1. about the explicit disabling of
         * non-transparent mode and the disable->enable non-transparent mode
         * sequence.
         */
        intel_dp_set_lttpr_transparent_mode(intel_dp, true);

        if (!ret)
                return 0;

        lttpr_count = intel_dp_lttpr_count(intel_dp);

        /*
         * In case of unsupported number of LTTPRs or failing to switch to
         * non-transparent mode fall-back to transparent link training mode,
         * still taking into account any LTTPR common lane- rate/count limits.
         */
        if (lttpr_count == 0)
                return 0;

        if (!intel_dp_set_lttpr_transparent_mode(intel_dp, false)) {
                drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
                            "Switching to LTTPR non-transparent LT mode failed, fall-back to transparent mode\n");

                intel_dp_set_lttpr_transparent_mode(intel_dp, true);
                intel_dp_reset_lttpr_count(intel_dp);

                return 0;
        }

        for (i = 0; i < lttpr_count; i++)
                intel_dp_read_lttpr_phy_caps(intel_dp, DP_PHY_LTTPR(i));

        return lttpr_count;
}
EXPORT_SYMBOL(intel_dp_lttpr_init);

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;
        }
}

static u8 intel_dp_lttpr_voltage_max(struct intel_dp *intel_dp,
                                     enum drm_dp_phy dp_phy)
{
        const u8 *phy_caps = intel_dp_lttpr_phy_caps(intel_dp, dp_phy);

        if (drm_dp_lttpr_voltage_swing_level_3_supported(phy_caps))
                return DP_TRAIN_VOLTAGE_SWING_LEVEL_3;
        else
                return DP_TRAIN_VOLTAGE_SWING_LEVEL_2;
}

static u8 intel_dp_lttpr_preemph_max(struct intel_dp *intel_dp,
                                     enum drm_dp_phy dp_phy)
{
        const u8 *phy_caps = intel_dp_lttpr_phy_caps(intel_dp, dp_phy);

        if (drm_dp_lttpr_pre_emphasis_level_3_supported(phy_caps))
                return DP_TRAIN_PRE_EMPH_LEVEL_3;
        else
                return DP_TRAIN_PRE_EMPH_LEVEL_2;
}

static bool
intel_dp_phy_is_downstream_of_source(struct intel_dp *intel_dp,
                                     enum drm_dp_phy dp_phy)
{
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
        int lttpr_count = intel_dp_lttpr_count(intel_dp);

        drm_WARN_ON_ONCE(&i915->drm, lttpr_count == 0 && dp_phy != DP_PHY_DPRX);

        return lttpr_count == 0 || dp_phy == DP_PHY_LTTPR(lttpr_count - 1);
}

static u8 intel_dp_phy_voltage_max(struct intel_dp *intel_dp,
                                   const struct intel_crtc_state *crtc_state,
                                   enum drm_dp_phy dp_phy)
{
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
        u8 voltage_max;

        /*
         * Get voltage_max from the DPTX_PHY (source or LTTPR) upstream from
         * the DPRX_PHY we train.
         */
        if (intel_dp_phy_is_downstream_of_source(intel_dp, dp_phy))
                voltage_max = intel_dp->voltage_max(intel_dp, crtc_state);
        else
                voltage_max = intel_dp_lttpr_voltage_max(intel_dp, dp_phy + 1);

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

        return voltage_max;
}

static u8 intel_dp_phy_preemph_max(struct intel_dp *intel_dp,
                                   enum drm_dp_phy dp_phy)
{
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
        u8 preemph_max;

        /*
         * Get preemph_max from the DPTX_PHY (source or LTTPR) upstream from
         * the DPRX_PHY we train.
         */
        if (intel_dp_phy_is_downstream_of_source(intel_dp, dp_phy))
                preemph_max = intel_dp->preemph_max(intel_dp);
        else
                preemph_max = intel_dp_lttpr_preemph_max(intel_dp, dp_phy + 1);

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

        return preemph_max;
}

void
intel_dp_get_adjust_train(struct intel_dp *intel_dp,
                          const struct intel_crtc_state *crtc_state,
                          enum drm_dp_phy dp_phy,
                          const u8 link_status[DP_LINK_STATUS_SIZE])
{
        u8 v = 0;
        u8 p = 0;
        int lane;
        u8 voltage_max;
        u8 preemph_max;

        for (lane = 0; lane < crtc_state->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_phy_preemph_max(intel_dp, dp_phy);
        if (p >= preemph_max)
                p = preemph_max | DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;

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

        voltage_max = intel_dp_phy_voltage_max(intel_dp, crtc_state, dp_phy);
        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 int intel_dp_training_pattern_set_reg(struct intel_dp *intel_dp,
                                             enum drm_dp_phy dp_phy)
{
        return dp_phy == DP_PHY_DPRX ?
                DP_TRAINING_PATTERN_SET :
                DP_TRAINING_PATTERN_SET_PHY_REPEATER(dp_phy);
}

static bool
intel_dp_set_link_train(struct intel_dp *intel_dp,
                        const struct intel_crtc_state *crtc_state,
                        enum drm_dp_phy dp_phy,
                        u8 dp_train_pat)
{
        int reg = intel_dp_training_pattern_set_reg(intel_dp, dp_phy);
        u8 buf[sizeof(intel_dp->train_set) + 1];
        int len;

        intel_dp_program_link_training_pattern(intel_dp, crtc_state,
                                               dp_train_pat);

        buf[0] = dp_train_pat;
        /* DP_TRAINING_LANEx_SET follow DP_TRAINING_PATTERN_SET */
        memcpy(buf + 1, intel_dp->train_set, crtc_state->lane_count);
        len = crtc_state->lane_count + 1;

        return drm_dp_dpcd_write(&intel_dp->aux, reg, buf, len) == len;
}

static bool
intel_dp_reset_link_train(struct intel_dp *intel_dp,
                          const struct intel_crtc_state *crtc_state,
                          enum drm_dp_phy dp_phy,
                          u8 dp_train_pat)
{
        memset(intel_dp->train_set, 0, sizeof(intel_dp->train_set));
        intel_dp_set_signal_levels(intel_dp, crtc_state);
        return intel_dp_set_link_train(intel_dp, crtc_state, dp_phy, dp_train_pat);
}

static bool
intel_dp_update_link_train(struct intel_dp *intel_dp,
                           const struct intel_crtc_state *crtc_state,
                           enum drm_dp_phy dp_phy)
{
        int reg = dp_phy == DP_PHY_DPRX ?
                            DP_TRAINING_LANE0_SET :
                            DP_TRAINING_LANE0_SET_PHY_REPEATER(dp_phy);
        int ret;

        intel_dp_set_signal_levels(intel_dp, crtc_state);

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

        return ret == crtc_state->lane_count;
}

static bool intel_dp_link_max_vswing_reached(struct intel_dp *intel_dp,
                                             const struct intel_crtc_state *crtc_state)
{
        int lane;

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

        return true;
}

/*
 * Prepare link training by configuring the link parameters. On DDI platforms
 * also enable the port here.
 */
static bool
intel_dp_prepare_link_train(struct intel_dp *intel_dp,
                            const struct intel_crtc_state *crtc_state)
{
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
        u8 link_config[2];
        u8 link_bw, rate_select;

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

        intel_dp_compute_rate(intel_dp, crtc_state->port_clock,
                              &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] = crtc_state->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;

        return true;
}

static void intel_dp_link_training_clock_recovery_delay(struct intel_dp *intel_dp,
                                                        enum drm_dp_phy dp_phy)
{
        if (dp_phy == DP_PHY_DPRX)
                drm_dp_link_train_clock_recovery_delay(intel_dp->dpcd);
        else
                drm_dp_lttpr_link_train_clock_recovery_delay();
}

/*
 * Perform the link training clock recovery phase on the given DP PHY using
 * training pattern 1.
 */
static bool
intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp,
                                      const struct intel_crtc_state *crtc_state,
                                      enum drm_dp_phy dp_phy)
{
        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;

        /* clock recovery */
        if (!intel_dp_reset_link_train(intel_dp, crtc_state, dp_phy,
                                       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];

                intel_dp_link_training_clock_recovery_delay(intel_dp, dp_phy);

                if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, dp_phy,
                                                     link_status) < 0) {
                        drm_err(&i915->drm, "failed to get link status\n");
                        return false;
                }

                if (drm_dp_clock_recovery_ok(link_status, crtc_state->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, crtc_state, dp_phy,
                                          link_status);
                if (!intel_dp_update_link_train(intel_dp, crtc_state, dp_phy)) {
                        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, crtc_state))
                        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,
                                     const struct intel_crtc_state *crtc_state,
                                     enum drm_dp_phy dp_phy)
{
        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.
         * LTTPRs must support TPS4.
         */
        source_tps4 = intel_dp_source_supports_hbr3(intel_dp);
        sink_tps4 = dp_phy != DP_PHY_DPRX ||
                    drm_dp_tps4_supported(intel_dp->dpcd);
        if (source_tps4 && sink_tps4) {
                return DP_TRAINING_PATTERN_4;
        } else if (crtc_state->port_clock == 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 = dp_phy != DP_PHY_DPRX ||
                    drm_dp_tps3_supported(intel_dp->dpcd);
        if (source_tps3 && sink_tps3) {
                return  DP_TRAINING_PATTERN_3;
        } else if (crtc_state->port_clock >= 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 void
intel_dp_link_training_channel_equalization_delay(struct intel_dp *intel_dp,
                                                  enum drm_dp_phy dp_phy)
{
        if (dp_phy == DP_PHY_DPRX) {
                drm_dp_link_train_channel_eq_delay(intel_dp->dpcd);
        } else {
                const u8 *phy_caps = intel_dp_lttpr_phy_caps(intel_dp, dp_phy);

                drm_dp_lttpr_link_train_channel_eq_delay(phy_caps);
        }
}

/*
 * Perform the link training channel equalization phase on the given DP PHY
 * using one of training pattern 2, 3 or 4 depending on the source and
 * sink capabilities.
 */
static bool
intel_dp_link_training_channel_equalization(struct intel_dp *intel_dp,
                                            const struct intel_crtc_state *crtc_state,
                                            enum drm_dp_phy dp_phy)
{
        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, crtc_state, dp_phy);
        /* 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, crtc_state, dp_phy,
                                     training_pattern)) {
                drm_err(&i915->drm, "failed to start channel equalization\n");
                return false;
        }

        for (tries = 0; tries < 5; tries++) {
                intel_dp_link_training_channel_equalization_delay(intel_dp,
                                                                  dp_phy);
                if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, dp_phy,
                                                     link_status) < 0) {
                        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,
                                              crtc_state->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,
                                         crtc_state->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, crtc_state, dp_phy,
                                          link_status);
                if (!intel_dp_update_link_train(intel_dp, crtc_state, dp_phy)) {
                        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");
        }

        return channel_eq;
}

static bool intel_dp_disable_dpcd_training_pattern(struct intel_dp *intel_dp,
                                                   enum drm_dp_phy dp_phy)
{
        int reg = intel_dp_training_pattern_set_reg(intel_dp, dp_phy);
        u8 val = DP_TRAINING_PATTERN_DISABLE;

        return drm_dp_dpcd_write(&intel_dp->aux, reg, &val, 1) == 1;
}

/**
 * intel_dp_stop_link_train - stop link training
 * @intel_dp: DP struct
 * @crtc_state: state for CRTC attached to the encoder
 *
 * Stop the link training of the @intel_dp port, disabling the test pattern
 * symbol generation on the port and disabling the training pattern in
 * the sink's DPCD.
 *
 * What symbols are output on the port after this point is
 * platform specific: On DDI/VLV/CHV platforms it will be the idle pattern
 * with the pipe being disabled, on older platforms it's HW specific if/how an
 * idle pattern is generated, as the pipe is already enabled here for those.
 *
 * This function must be called after intel_dp_start_link_train().
 */
void intel_dp_stop_link_train(struct intel_dp *intel_dp,
                              const struct intel_crtc_state *crtc_state)
{
        intel_dp->link_trained = true;

        intel_dp_program_link_training_pattern(intel_dp,
                                               crtc_state,
                                               DP_TRAINING_PATTERN_DISABLE);
        intel_dp_disable_dpcd_training_pattern(intel_dp, DP_PHY_DPRX);
}

static bool
intel_dp_link_train_phy(struct intel_dp *intel_dp,
                        const struct intel_crtc_state *crtc_state,
                        enum drm_dp_phy dp_phy)
{
        struct intel_connector *intel_connector = intel_dp->attached_connector;
        char phy_name[10];
        bool ret = false;

        if (!intel_dp_link_training_clock_recovery(intel_dp, crtc_state, dp_phy))
                goto out;

        if (!intel_dp_link_training_channel_equalization(intel_dp, crtc_state, dp_phy))
                goto out;

        ret = true;

out:
        drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
                    "[CONNECTOR:%d:%s] Link Training %s at link rate = %d, lane count = %d, at %s",
                    intel_connector->base.base.id,
                    intel_connector->base.name,
                    ret ? "passed" : "failed",
                    crtc_state->port_clock, crtc_state->lane_count,
                    intel_dp_phy_name(dp_phy, phy_name, sizeof(phy_name)));

        return ret;
}

static void intel_dp_schedule_fallback_link_training(struct intel_dp *intel_dp,
                                                     const struct intel_crtc_state *crtc_state)
{
        struct intel_connector *intel_connector = intel_dp->attached_connector;

        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,
                                                           crtc_state->port_clock,
                                                           crtc_state->lane_count)) {
                return;
        }

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

/* Perform the link training on all LTTPRs and the DPRX on a link. */
static bool
intel_dp_link_train_all_phys(struct intel_dp *intel_dp,
                             const struct intel_crtc_state *crtc_state,
                             int lttpr_count)
{
        bool ret = true;
        int i;

        intel_dp_prepare_link_train(intel_dp, crtc_state);

        for (i = lttpr_count - 1; i >= 0; i--) {
                enum drm_dp_phy dp_phy = DP_PHY_LTTPR(i);

                ret = intel_dp_link_train_phy(intel_dp, crtc_state, dp_phy);
                intel_dp_disable_dpcd_training_pattern(intel_dp, dp_phy);

                if (!ret)
                        break;
        }

        if (ret)
                intel_dp_link_train_phy(intel_dp, crtc_state, DP_PHY_DPRX);

        if (intel_dp->set_idle_link_train)
                intel_dp->set_idle_link_train(intel_dp, crtc_state);

        return ret;
}

/**
 * intel_dp_start_link_train - start link training
 * @intel_dp: DP struct
 * @crtc_state: state for CRTC attached to the encoder
 *
 * Start the link training of the @intel_dp port, scheduling a fallback
 * retraining with reduced link rate/lane parameters if the link training
 * fails.
 * After calling this function intel_dp_stop_link_train() must be called.
 */
void intel_dp_start_link_train(struct intel_dp *intel_dp,
                               const struct intel_crtc_state *crtc_state)
{
        /*
         * TODO: Reiniting LTTPRs here won't be needed once proper connector
         * HW state readout is added.
         */
        int lttpr_count = intel_dp_lttpr_init(intel_dp);

        if (!intel_dp_link_train_all_phys(intel_dp, crtc_state, lttpr_count))
                intel_dp_schedule_fallback_link_training(intel_dp, crtc_state);
}