[Intel-gfx] [PATCH v6 2/3] drm/i915: Check DP no aux transaction bit on link training

[Mika Kahola]

Check if *NO_AUX_TRANSACTIONS_LINK_TRAINING* bit is set on
DPCD registers. If this bit is set, we can reuse the known
good drive current and pre-emphasis level from the last
"full" link training.

v2: Commit message update (Thierry)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91393
Signed-off-by: Mika Kahola <mika.kahola at intel.com>
---
 drivers/gpu/drm/i915/intel_dp.c               |  2 +-
 drivers/gpu/drm/i915/intel_dp_link_training.c | 19 +++++++++++++++++++
 drivers/gpu/drm/i915/intel_drv.h              |  1 +
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 6b36d82..3137187 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -3852,7 +3852,7 @@ intel_dp_link_down(struct intel_dp *intel_dp)
 	intel_dp->DP = DP;
 }
 
-static bool
+bool
 intel_dp_get_dpcd(struct intel_dp *intel_dp)
 {
 	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
diff --git a/drivers/gpu/drm/i915/intel_dp_link_training.c b/drivers/gpu/drm/i915/intel_dp_link_training.c
index 8f22c92..bcf2801 100644
--- a/drivers/gpu/drm/i915/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/intel_dp_link_training.c
@@ -85,6 +85,25 @@ static bool
 intel_dp_reset_link_train(struct intel_dp *intel_dp,
 			uint8_t dp_train_pat)
 {
+	bool has_dpcd;
+	bool no_aux_handshake = false;
+
+	has_dpcd = intel_dp_get_dpcd(intel_dp);
+
+	/*
+	 * Source device can try to use drive current and pre-emphasis
+	 * parameters computed by the last "full" link training if the
+	 * DP_NO_AUX_HANDSHAKE_LINK_TRAINING bit is set to 1.
+	 */
+	if (has_dpcd) {
+		if (intel_dp->dpcd[DP_DPCD_REV] >= 0x11) {
+			no_aux_handshake = (intel_dp->dpcd[DP_MAX_DOWNSPREAD] &
+					    DP_NO_AUX_HANDSHAKE_LINK_TRAINING);
+		}
+	}
+
+	intel_dp->train_set_valid &= no_aux_handshake;
+
 	DRM_DEBUG_KMS("link training optimization: %s\n",
 		      yesno(intel_dp->train_set_valid));
 
diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
index 0438b57..918bdf1 100644
--- a/drivers/gpu/drm/i915/intel_drv.h
+++ b/drivers/gpu/drm/i915/intel_drv.h
@@ -1250,6 +1250,7 @@ int intel_dp_sink_crc(struct intel_dp *intel_dp, u8 *crc);
 bool intel_dp_compute_config(struct intel_encoder *encoder,
 			     struct intel_crtc_state *pipe_config);
 bool intel_dp_is_edp(struct drm_device *dev, enum port port);
+bool intel_dp_get_dpcd(struct intel_dp *intel_dp);
 enum irqreturn intel_dp_hpd_pulse(struct intel_digital_port *intel_dig_port,
 				  bool long_hpd);
 void intel_edp_backlight_on(struct intel_dp *intel_dp);
-- 
1.9.1