[PATCH 37/38][SRU][G/H] UBUNTU SAUCE: drm/i915: Switch to LTTPR transparent mode link training

[You-Sheng Yang]

From: Imre Deak <imre.deak at intel.com>

BugLink: https://bugs.launchpad.net/bugs/1903969

By default LTTPRs should be in transparent link training mode,
nevertheless in this patch we switch to this default mode explicitly.

The DP Standard recommends this, supposedly because an LTTPR may be left
in the non-transparent mode (by BIOS, previous kernel, or after reset
due to a firmware bug). I haven't seen this happening, but let's follow
the DP Standard.

v2:
- Add a code comment about the explicit disabling of non-transparent
  mode.
v3:
- Move check to prevent initing LTTPRs on eDP to init_dp_lttpr_init().

Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Signed-off-by: Imre Deak <imre.deak at intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201007170917.1764556-6-imre.deak@intel.com
(backported from commit 7b2a4ab8b0ef2a6dbec0b15d2cabf5a9e7acdf4c
https://anongit.freedesktop.org/git/drm-tip.git)
Signed-off-by: You-Sheng Yang <vicamo.yang at canonical.com>
---
 .../drm/i915/display/intel_display_types.h    |  1 +
 drivers/gpu/drm/i915/display/intel_dp.c       |  2 +
 .../drm/i915/display/intel_dp_link_training.c | 55 +++++++++++++++++++
 .../drm/i915/display/intel_dp_link_training.h |  2 +
 4 files changed, 60 insertions(+)

diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
index da11ebad19f8..6dbed0a56808 100644
--- a/drivers/gpu/drm/i915/display/intel_display_types.h
+++ b/drivers/gpu/drm/i915/display/intel_display_types.h
@@ -1284,6 +1284,7 @@ struct intel_dp {
 	u8 downstream_ports[DP_MAX_DOWNSTREAM_PORTS];
 	u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE];
 	u8 dsc_dpcd[DP_DSC_RECEIVER_CAP_SIZE];
+	u8 lttpr_common_caps[DP_LTTPR_COMMON_CAP_SIZE];
 	u8 fec_capable;
 	/* source rates */
 	int num_source_rates;
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index 53468eddff64..2d7370692295 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -4628,6 +4628,8 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp)
 static bool
 intel_dp_get_dpcd(struct intel_dp *intel_dp)
 {
+	intel_dp_lttpr_init(intel_dp);
+
 	if (!intel_dp_read_dpcd(intel_dp))
 		return false;
 
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 41fb2d2b66ab..6a64ce5d6d6d 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -34,6 +34,55 @@ intel_dp_dump_link_status(const u8 link_status[DP_LINK_STATUS_SIZE])
 		      link_status[3], link_status[4], link_status[5]);
 }
 
+static bool intel_dp_read_lttpr_common_caps(struct intel_dp *intel_dp)
+{
+	if (drm_dp_read_lttpr_common_caps(&intel_dp->aux,
+					  intel_dp->lttpr_common_caps) < 0) {
+		memset(intel_dp->lttpr_common_caps, 0,
+		       sizeof(intel_dp->lttpr_common_caps));
+		return false;
+	}
+
+	drm_dbg_kms(&dp_to_i915(intel_dp)->drm,
+		    "LTTPR common capabilities: %*ph\n",
+		    (int)sizeof(intel_dp->lttpr_common_caps),
+		    intel_dp->lttpr_common_caps);
+
+	return true;
+}
+
+static bool
+intel_dp_set_lttpr_transparent_mode(struct intel_dp *intel_dp, bool enable)
+{
+	u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
+			  DP_PHY_REPEATER_MODE_NON_TRANSPARENT;
+
+	return drm_dp_dpcd_write(&intel_dp->aux, DP_PHY_REPEATER_MODE, &val, 1) == 1;
+}
+
+/**
+ * intel_dp_lttpr_init - detect LTTPRs and init the LTTPR link training mode
+ * @intel_dp: Intel DP struct
+ *
+ * Read the LTTPR common capabilities and switch to transparent link training
+ * mode.
+ */
+int intel_dp_lttpr_init(struct intel_dp *intel_dp)
+{
+	if (intel_dp_is_edp(intel_dp))
+		return 0;
+
+	intel_dp_read_lttpr_common_caps(intel_dp);
+
+	/*
+	 * See DP Standard v2.0 3.6.6.1. about the explicit disabling of
+	 * non-transparent mode.
+	 */
+	intel_dp_set_lttpr_transparent_mode(intel_dp, true);
+
+	return 0;
+}
+
 static u8 dp_voltage_max(u8 preemph)
 {
 	switch (preemph & DP_TRAIN_PRE_EMPHASIS_MASK) {
@@ -483,6 +532,12 @@ static void intel_dp_schedule_fallback_link_training(struct intel_dp *intel_dp,
 void intel_dp_start_link_train(struct intel_dp *intel_dp,
 			       const struct intel_crtc_state *crtc_state)
 {
+	/*
+	 * TODO: Reiniting LTTPRs here won't be needed once proper connector
+	 * HW state readout is added.
+	 */
+	intel_dp_lttpr_init(intel_dp);
+
 	if (!intel_dp_link_train(intel_dp, crtc_state))
 		intel_dp_schedule_fallback_link_training(intel_dp, crtc_state);
 }
diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.h b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
index bf9474e41aed..b3fb1d125b9b 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.h
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
@@ -11,6 +11,8 @@
 struct intel_crtc_state;
 struct intel_dp;
 
+int intel_dp_lttpr_init(struct intel_dp *intel_dp);
+
 void intel_dp_get_adjust_train(struct intel_dp *intel_dp,
 			       const struct intel_crtc_state *crtc_state,
 			       const u8 link_status[DP_LINK_STATUS_SIZE]);
-- 
2.29.2