[Intel-gfx] [PATCH] drm/i915/dp: DPTX writes Swing/Pre-emphs(DPCD 0x103-0x106) requested during PHY Layer testing.

[Khaled Almahallawy]

Source needs to write DPCD 103-106 after receiving a PHY request to change
swing/pre-emphasis after reading DPCD 206-207. This is especially needed if
there is a retimer between source and sink and the retimer implements AUX_CH
interception scheme to manage DP PHY settings (e.g. adjusting Swing/Pre-emphasis
equalization level) for DP output channel . If the source doesn't write to
DPCD 103-106, the retimer may not output the requested swing/pre-emphasis and
eventually we fail compliance.

Signed-off-by: Khaled Almahallawy <khaled.almahallawy at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dp.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 79c27f91f42c..5044201ca742 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -5503,6 +5503,9 @@ void intel_dp_process_phy_request(struct intel_dp *intel_dp)
 
 	intel_dp_autotest_phy_ddi_enable(intel_dp, data->num_lanes);
 
+	drm_dp_dpcd_write(&intel_dp->aux, DP_TRAINING_LANE0_SET,
+				intel_dp->train_set, intel_dp->lane_count);
+
 	drm_dp_set_phy_test_pattern(&intel_dp->aux, data,
 				    link_status[DP_DPCD_REV]);
 }
-- 
2.17.1