drm/i915: Fix DP clock recovery "voltage_tries" handling

The DP spec says:
"If the receiver keeps the same value in the ADJUST_REQUEST_LANEx_y
 register(s) while the LANEx_CR_DONE bits remain unset, the transmitter
 must loop four times with the same voltage swing. On the fifth time,
 the transmitter must down-shift to the lower bit rate and must repeat
 the CR-lock training sequence as described below."

Lets fix the code to follow that instead of terminating after five
times of transmitting the same signal levels. The text in spec feels
a little bit ambiguous still, but this is my best guess at its meaning.

As a bonus this also gets rid of the train_set[0] stuff which
would not work for per-lane drive settings anyway.

Cc: Imre Deak <imre.deak@intel.com>
CC: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211001160826.17080-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>

diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
index 053ed93..73a823f 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -511,6 +511,25 @@ static void intel_dp_link_training_clock_recovery_delay(struct intel_dp *intel_d
                drm_dp_lttpr_link_train_clock_recovery_delay();
 }
 
+static bool intel_dp_adjust_request_changed(int lane_count,
+                                           const u8 old_link_status[DP_LINK_STATUS_SIZE],
+                                           const u8 new_link_status[DP_LINK_STATUS_SIZE])
+{
+       int lane;
+
+       for (lane = 0; lane < lane_count; lane++) {
+               u8 old = drm_dp_get_adjust_request_voltage(old_link_status, lane) |
+                       drm_dp_get_adjust_request_pre_emphasis(old_link_status, lane);
+               u8 new = drm_dp_get_adjust_request_voltage(new_link_status, lane) |
+                       drm_dp_get_adjust_request_pre_emphasis(new_link_status, lane);
+
+               if (old != new)
+                       return true;
+       }
+
+       return false;
+}
+
 /*
  * Perform the link training clock recovery phase on the given DP PHY using
  * training pattern 1.
@@ -521,7 +540,7 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp,
                                      enum drm_dp_phy dp_phy)
 {
        struct drm_i915_private *i915 = dp_to_i915(intel_dp);
-       u8 voltage;
+       u8 old_link_status[DP_LINK_STATUS_SIZE] = {};
        int voltage_tries, cr_tries, max_cr_tries;
        bool max_vswing_reached = false;
 
@@ -574,8 +593,6 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp,
                        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);
@@ -585,12 +602,14 @@ intel_dp_link_training_clock_recovery(struct intel_dp *intel_dp,
                        return false;
                }
 
-               if ((intel_dp->train_set[0] & DP_TRAIN_VOLTAGE_SWING_MASK) ==
-                   voltage)
+               if (!intel_dp_adjust_request_changed(crtc_state->lane_count,
+                                                    old_link_status, link_status))
                        ++voltage_tries;
                else
                        voltage_tries = 1;
 
+               memcpy(old_link_status, link_status, sizeof(link_status));
+
                if (intel_dp_link_max_vswing_reached(intel_dp, crtc_state))
                        max_vswing_reached = true;