drm/i915: Fix DP_TRAIN_MAX_{PRE_EMPHASIS,SWING}_REACHED handling

The DP spec says:
"The transmitter shall support at least three levels of voltage
 swing (Levels 0, 1, and 2).

 If only three levels of voltage swing are supported (VOLTAGE
 SWING SET field (bits 1:0) are programmed to 10 (Level 2)),
 this bit shall be set to 1, and cleared in all other cases.

 If all four levels of voltage swing are supported (VOLTAGE
 SWING SET field (bits 1:0) are programmed to 11 (Level 3)),
 this bit shall be set to 1,and cleared in all other cases."

Let's follow that exactly instead of the current apporach
where we can set those also for vswing/preemph levels 0 or 1
(or 2 when the platform max is 3).

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200512174145.3186-7-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 b9e4ee2dbddc9b75d80e2388ebaccf25c156c85f..2493142a70e97e4451a10f5058ecbf4c2f6c2665 100644 (file)
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -67,8 +67,9 @@ void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
        if (p >= preemph_max)
                p = preemph_max | DP_TRAIN_MAX_PRE_EMPHASIS_REACHED;
 
-       voltage_max = min(intel_dp->voltage_max(intel_dp),
-                         dp_voltage_max(p));
+       v = min(v, dp_voltage_max(p));
+
+       voltage_max = intel_dp->voltage_max(intel_dp);
        if (v >= voltage_max)
                v = voltage_max | DP_TRAIN_MAX_SWING_REACHED;