According to the DisplayPort Spec, in case of Clock Recovery failure
the link training sequence should fall back to the lower link rate
followed by lower lane count until CR succeeds.
On CR success, the sequence proceeds with Channel EQ.
In case of Channel EQ failures, it should fallback to
lower link rate and lane count and start the CR phase again.

v7:
* Address readability concerns (Mika Kahola)
v6:
* Do not split quoted string across line (Mika Kahola)
v5:
* Reset the link rate index to the max link rate index
before lowering the lane count (Jani Nikula)
* Use the paradigm for loop in intel_dp_link_rate_index
v4:
* Fixed the link rate fallback loop (Manasi Navare)
v3:
* Fixed some rebase issues (Mika Kahola)
v2:
* Add a helper function to return index of requested link rate
into common_rates array
* Changed the link rate fallback loop to make use
of common_rates array (Mika Kahola)
* Changed INTEL_INFO to INTEL_GEN (David Weinehall)

Signed-off-by: Manasi Navare <manasi.d.nav...@intel.com>
---
 drivers/gpu/drm/i915/intel_ddi.c              | 113 +++++++++++++++++++++++---
 drivers/gpu/drm/i915/intel_dp.c               |  15 ++++
 drivers/gpu/drm/i915/intel_dp_link_training.c |  13 ++-
 drivers/gpu/drm/i915/intel_drv.h              |   6 +-
 4 files changed, 133 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 8065a5f..093038c 100644
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -1637,19 +1637,18 @@ void intel_ddi_clk_select(struct intel_encoder *encoder,
        }
 }
 
-static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
+static void intel_ddi_pre_enable_edp(struct intel_encoder *encoder,
                                    int link_rate, uint32_t lane_count,
-                                   struct intel_shared_dpll *pll,
-                                   bool link_mst)
+                                   struct intel_shared_dpll *pll)
 {
        struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
        struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
        enum port port = intel_ddi_get_encoder_port(encoder);
 
        intel_dp_set_link_params(intel_dp, link_rate, lane_count,
-                                link_mst);
-       if (encoder->type == INTEL_OUTPUT_EDP)
-               intel_edp_panel_on(intel_dp);
+                                false);
+
+       intel_edp_panel_on(intel_dp);
 
        intel_ddi_clk_select(encoder, pll);
        intel_prepare_dp_ddi_buffers(encoder);
@@ -1660,6 +1659,28 @@ static void intel_ddi_pre_enable_dp(struct intel_encoder 
*encoder,
                intel_dp_stop_link_train(intel_dp);
 }
 
+static void intel_ddi_pre_enable_dp(struct intel_encoder *encoder,
+                                   int link_rate, uint32_t lane_count,
+                                   struct intel_shared_dpll *pll,
+                                   bool link_mst)
+{
+       struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
+       struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
+       struct intel_shared_dpll_config tmp_pll_config;
+
+       /* Disable the PLL and obtain the PLL for Link Training
+        * that starts with highest link rate and lane count.
+        */
+       tmp_pll_config = pll->config;
+       pll->funcs.disable(dev_priv, pll);
+       pll->config.crtc_mask = 0;
+
+       /* If Link Training fails, send a uevent to generate a hotplug */
+       if (!intel_ddi_link_train(intel_dp, link_rate, lane_count, link_mst))
+               drm_kms_helper_hotplug_event(encoder->base.dev);
+       pll->config = tmp_pll_config;
+}
+
 static void intel_ddi_pre_enable_hdmi(struct intel_encoder *encoder,
                                      bool has_hdmi_sink,
                                      struct drm_display_mode *adjusted_mode,
@@ -1693,20 +1714,26 @@ static void intel_ddi_pre_enable(struct intel_encoder 
*intel_encoder,
        struct intel_crtc *crtc = to_intel_crtc(encoder->crtc);
        int type = intel_encoder->type;
 
-       if (type == INTEL_OUTPUT_DP || type == INTEL_OUTPUT_EDP) {
+       if (type == INTEL_OUTPUT_EDP)
+               intel_ddi_pre_enable_edp(intel_encoder,
+                                       crtc->config->port_clock,
+                                       crtc->config->lane_count,
+                                       crtc->config->shared_dpll);
+
+       if (type == INTEL_OUTPUT_DP)
                intel_ddi_pre_enable_dp(intel_encoder,
                                        crtc->config->port_clock,
                                        crtc->config->lane_count,
                                        crtc->config->shared_dpll,
                                        intel_crtc_has_type(crtc->config,
                                                            
INTEL_OUTPUT_DP_MST));
-       }
-       if (type == INTEL_OUTPUT_HDMI) {
+
+       if (type == INTEL_OUTPUT_HDMI)
                intel_ddi_pre_enable_hdmi(intel_encoder,
                                          crtc->config->has_hdmi_sink,
                                          &crtc->config->base.adjusted_mode,
                                          crtc->config->shared_dpll);
-       }
+
 }
 
 static void intel_ddi_post_disable(struct intel_encoder *intel_encoder,
@@ -2435,6 +2462,72 @@ intel_ddi_get_link_dpll(struct intel_dp *intel_dp, int 
clock)
        return pll;
 }
 
+bool
+intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
+                    uint8_t max_lane_count, bool link_mst)
+{
+       struct intel_connector *connector = intel_dp->attached_connector;
+       struct intel_encoder *encoder = connector->encoder;
+       struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
+       struct intel_shared_dpll *pll;
+       struct intel_shared_dpll_config tmp_pll_config;
+       int link_rate, max_link_rate_index, link_rate_index;
+       uint8_t lane_count;
+       int common_rates[DP_MAX_SUPPORTED_RATES] = {};
+       bool ret = false;
+
+       max_link_rate_index = intel_dp_link_rate_index(intel_dp, common_rates,
+                                                      max_link_rate);
+       if (max_link_rate_index < 0) {
+               DRM_ERROR("Invalid Link Rate\n");
+               return false;
+       }
+
+       for (lane_count = max_lane_count; lane_count > 0; lane_count >>= 1) {
+               for (link_rate_index = max_link_rate_index;
+                    link_rate_index >= 0; link_rate_index--) {
+                       link_rate = common_rates[link_rate_index];
+                       pll = intel_ddi_get_link_dpll(intel_dp, link_rate);
+                       if (pll == NULL) {
+                               DRM_ERROR("Could not find DPLL for link 
training.\n");
+                               return false;
+                       }
+                       tmp_pll_config = pll->config;
+                       pll->funcs.enable(dev_priv, pll);
+
+                       intel_dp_set_link_params(intel_dp, link_rate,
+                                                lane_count, link_mst);
+
+                       intel_ddi_clk_select(encoder, pll);
+                       intel_prepare_dp_ddi_buffers(encoder);
+                       intel_ddi_init_dp_buf_reg(encoder);
+                       intel_dp_sink_dpms(intel_dp, DRM_MODE_DPMS_ON);
+                       ret = intel_dp_start_link_train(intel_dp);
+                       if (ret)
+                               break;
+
+                       /* Disable port followed by PLL for next
+                        *retry/clean up
+                        */
+                       intel_ddi_post_disable(encoder, NULL, NULL);
+                       pll->funcs.disable(dev_priv, pll);
+                       pll->config = tmp_pll_config;
+               }
+               if (ret) {
+                       DRM_DEBUG_KMS("Link Training successful at link rate: 
%d lane: %d\n",
+                                     link_rate, lane_count);
+                       break;
+               }
+       }
+
+       intel_dp_stop_link_train(intel_dp);
+
+       if (!lane_count)
+               DRM_ERROR("Link Training Failed\n");
+
+       return ret;
+}
+
 void intel_ddi_init(struct drm_device *dev, enum port port)
 {
        struct drm_i915_private *dev_priv = to_i915(dev);
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 69cee9b..d81c67cb 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1506,6 +1506,21 @@ intel_dp_max_link_rate(struct intel_dp *intel_dp)
        return rates[len - 1];
 }
 
+int intel_dp_link_rate_index(struct intel_dp *intel_dp, int *common_rates,
+                            int link_rate)
+{
+       int common_len;
+       int index;
+
+       common_len = intel_dp_common_rates(intel_dp, common_rates);
+       for (index = 0; index < common_len; index++) {
+               if (link_rate == common_rates[common_len - index - 1])
+                       return common_len - index - 1;
+       }
+
+       return -1;
+}
+
 int intel_dp_rate_select(struct intel_dp *intel_dp, int rate)
 {
        return rate_to_index(rate, intel_dp->sink_rates);
diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c 
b/drivers/gpu/drm/i915/intel_dp_link_training.c
index c438b02..6eb5eb6 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -313,9 +313,16 @@ void intel_dp_stop_link_train(struct intel_dp *intel_dp)
                                DP_TRAINING_PATTERN_DISABLE);
 }
 
-void
+bool
 intel_dp_start_link_train(struct intel_dp *intel_dp)
 {
-       intel_dp_link_training_clock_recovery(intel_dp);
-       intel_dp_link_training_channel_equalization(intel_dp);
+       bool ret;
+
+       if (intel_dp_link_training_clock_recovery(intel_dp)) {
+               ret = intel_dp_link_training_channel_equalization(intel_dp);
+               if (ret)
+                       return true;
+       }
+
+       return false;
 }
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 8fd16ad..08cb571 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1164,6 +1164,8 @@ void intel_ddi_clock_get(struct intel_encoder *encoder,
                         struct intel_crtc_state *pipe_config);
 void intel_ddi_set_vc_payload_alloc(struct drm_crtc *crtc, bool state);
 uint32_t ddi_signal_levels(struct intel_dp *intel_dp);
+bool intel_ddi_link_train(struct intel_dp *intel_dp, int max_link_rate,
+                         uint8_t max_lane_count, bool link_mst);
 struct intel_shared_dpll *intel_ddi_get_link_dpll(struct intel_dp *intel_dp,
                                                  int clock);
 unsigned int intel_fb_align_height(struct drm_device *dev,
@@ -1385,7 +1387,7 @@ bool intel_dp_init_connector(struct intel_digital_port 
*intel_dig_port,
 void intel_dp_set_link_params(struct intel_dp *intel_dp,
                              int link_rate, uint8_t lane_count,
                              bool link_mst);
-void intel_dp_start_link_train(struct intel_dp *intel_dp);
+bool intel_dp_start_link_train(struct intel_dp *intel_dp);
 void intel_dp_stop_link_train(struct intel_dp *intel_dp);
 void intel_dp_sink_dpms(struct intel_dp *intel_dp, int mode);
 void intel_dp_encoder_reset(struct drm_encoder *encoder);
@@ -1407,6 +1409,8 @@ void intel_dp_add_properties(struct intel_dp *intel_dp, 
struct drm_connector *co
 void intel_dp_mst_suspend(struct drm_device *dev);
 void intel_dp_mst_resume(struct drm_device *dev);
 int intel_dp_max_link_rate(struct intel_dp *intel_dp);
+int intel_dp_link_rate_index(struct intel_dp *intel_dp, int *common_rates,
+                            int link_rate);
 int intel_dp_rate_select(struct intel_dp *intel_dp, int rate);
 void intel_dp_hot_plug(struct intel_encoder *intel_encoder);
 void intel_power_sequencer_reset(struct drm_i915_private *dev_priv);
-- 
1.9.1

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