[Intel-gfx] [PATCH v2 5/8] drm/i915/dp: rewrite DP 2.0 128b/132b link training based on errata

Jani Nikula
2022-02-03T09:04:31Z

The DP 2.0 errata completely overhauls the 128b/132b link training, with
no provisions for backward compatibility with the original DP 2.0
specification.

The changes are too intrusive to consider reusing the same code for both
8b/10b and 128b/132b, mainly because the LTTPR channel equalisation is
done concurrently instead of serialized.

NOTES:

* It's a bit unclear when to wait for DP_INTERLANE_ALIGN_DONE and
per-lane DP_LANE_SYMBOL_LOCKED. Figure xx4 in the SCR implies the
LANEx_CHANNEL_EQ_DONE sequence may end with either 0x77,0x77,0x85 *or*
0x33,0x33,0x84 (for four lane configuration in DPCD 0x202..0x204)
i.e. without the above bits set. Text elsewhere seems contradictory or
incomplete.

* We read entire link status (6 bytes) everywhere instead of individual
DPCD addresses.

* There are some subtle ambiguities or contradictions in the order of
some DPCD access and TPS signal enables/disables. It's also not clear
whether these are significant.

v2:
- Always try one last time after timeouts to avoid races (Ville)
- Extend timeout to cover the entire LANEx_EQ_DONE sequence (Ville)
- Also check for eq interlane align done in LANEx_CDS_DONE Sequence (Ville)
- Check for Intra-hop status before link training

Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
---
.../drm/i915/display/intel_dp_link_training.c | 279 +++++++++++++++++-
1 file changed, 278 insertions(+), 1 deletion(-)

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 4e507aa75a03..cc2b82d9114c 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
@@ -1102,6 +1102,277 @@ intel_dp_link_train_all_phys(struct intel_dp *intel_dp,
return ret;
}

+
+/*
+ * 128b/132b DP LANEx_EQ_DONE Sequence (DP 2.0 E11 3.5.2.16.1)
+ */
+static bool
+intel_dp_128b132b_lane_eq(struct intel_dp *intel_dp,
+ const struct intel_crtc_state *crtc_state)
+{
+ struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+ struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+ u8 link_status[DP_LINK_STATUS_SIZE];
+ int delay_us;
+ int try, max_tries = 20;
+ unsigned long deadline;
+ bool timeout = false;
+
+ /*
+ * Reset signal levels. Start transmitting 128b/132b TPS1.
+ *
+ * Put DPRX and LTTPRs (if any) into intra-hop AUX mode by writing TPS1
+ * in DP_TRAINING_PATTERN_SET.
+ */
+ if (!intel_dp_reset_link_train(intel_dp, crtc_state, DP_PHY_DPRX,
+ DP_TRAINING_PATTERN_1)) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to start 128b/132b TPS1\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ delay_us = drm_dp_128b132b_read_aux_rd_interval(&intel_dp->aux);
+
+ /* Read the initial TX FFE settings. */
+ if (drm_dp_dpcd_read_link_status(&intel_dp->aux, link_status) < 0) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to read TX FFE presets\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ /* Update signal levels and training set as requested. */
+ intel_dp_get_adjust_train(intel_dp, crtc_state, DP_PHY_DPRX, link_status);
+ if (!intel_dp_update_link_train(intel_dp, crtc_state, DP_PHY_DPRX)) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to set initial TX FFE settings\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ /* Start transmitting 128b/132b TPS2. */
+ if (!intel_dp_set_link_train(intel_dp, crtc_state, DP_PHY_DPRX,
+ DP_TRAINING_PATTERN_2)) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to start 128b/132b TPS2\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ /* Time budget for the LANEx_EQ_DONE Sequence */
+ deadline = jiffies + msecs_to_jiffies(400);
+
+ for (try = 0; try < max_tries; try++) {
+ usleep_range(delay_us, 2 * delay_us);
+
+ /*
+ * The delay may get updated. The transmitter shall read the
+ * delay before link status during link training.
+ */
+ delay_us = drm_dp_128b132b_read_aux_rd_interval(&intel_dp->aux);
+
+ if (drm_dp_dpcd_read_link_status(&intel_dp->aux, link_status) < 0) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to read link status\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (drm_dp_128b132b_link_training_failed(link_status)) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Downstream link training failure\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (drm_dp_128b132b_lane_channel_eq_done(link_status, crtc_state->lane_count)) {
+ drm_dbg_kms(&i915->drm,
+ "[ENCODER:%d:%s] Lane channel eq done\n",
+ encoder->base.base.id, encoder->base.name);
+ break;
+ }
+
+ if (timeout) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Lane channel eq timeout\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (time_after(jiffies, deadline))
+ timeout = true; /* try one last time after deadline */
+
+ /* Update signal levels and training set as requested. */
+ intel_dp_get_adjust_train(intel_dp, crtc_state, DP_PHY_DPRX, link_status);
+ if (!intel_dp_update_link_train(intel_dp, crtc_state, DP_PHY_DPRX)) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to update TX FFE settings\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+ }
+
+ if (try == max_tries) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Max loop count reached\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ for (;;) {
+ if (drm_dp_128b132b_eq_interlane_align_done(link_status)) {
+ drm_dbg_kms(&i915->drm,
+ "[ENCODER:%d:%s] Interlane align done\n",
+ encoder->base.base.id, encoder->base.name);
+ break;
+ }
+
+ if (timeout) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Interlane align timeout\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (time_after(jiffies, deadline))
+ timeout = true; /* try one last time after deadline */
+
+ usleep_range(2000, 3000);
+
+ if (drm_dp_dpcd_read_link_status(&intel_dp->aux, link_status) < 0) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to read link status\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (drm_dp_128b132b_link_training_failed(link_status)) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Downstream link training failure\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+ }
+
+ return true;
+}
+
+/*
+ * 128b/132b DP LANEx_CDS_DONE Sequence (DP 2.0 E11 3.5.2.16.2)
+ */
+static bool
+intel_dp_128b132b_lane_cds(struct intel_dp *intel_dp,
+ const struct intel_crtc_state *crtc_state,
+ int lttpr_count)
+{
+ struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+ struct drm_i915_private *i915 = to_i915(encoder->base.dev);
+ u8 link_status[DP_LINK_STATUS_SIZE];
+ unsigned long deadline;
+ bool timeout = false;
+
+ if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_TRAINING_PATTERN_SET,
+ DP_TRAINING_PATTERN_2_CDS) != 1) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to start 128b/132b TPS2 CDS\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ /* Time budget for the LANEx_CDS_DONE Sequence */
+ deadline = jiffies + msecs_to_jiffies((lttpr_count + 1) * 20);
+
+ for (;;) {
+ usleep_range(2000, 3000);
+
+ if (drm_dp_dpcd_read_link_status(&intel_dp->aux, link_status) < 0) {
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Failed to read link status\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (drm_dp_128b132b_eq_interlane_align_done(link_status) &&
+ drm_dp_128b132b_cds_interlane_align_done(link_status) &&
+ drm_dp_128b132b_lane_symbol_locked(link_status, crtc_state->lane_count)) {
+ drm_dbg_kms(&i915->drm,
+ "[ENCODER:%d:%s] CDS interlane align done\n",
+ encoder->base.base.id, encoder->base.name);
+ break;
+ }
+
+ if (drm_dp_128b132b_link_training_failed(link_status)) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] Downstream link training failure\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (timeout) {
+ intel_dp_dump_link_status(intel_dp, DP_PHY_DPRX, link_status);
+ drm_err(&i915->drm,
+ "[ENCODER:%d:%s] CDS timeout\n",
+ encoder->base.base.id, encoder->base.name);
+ return false;
+ }
+
+ if (time_after(jiffies, deadline))
+ timeout = true; /* try one last time after deadline */
+ }
+
+ /* FIXME: Should DP_TRAINING_PATTERN_DISABLE be written first? */
+ if (intel_dp->set_idle_link_train)
+ intel_dp->set_idle_link_train(intel_dp, crtc_state);
+
+ return true;
+}
+
+/*
+ * 128b/132b link training sequence. (DP 2.0 E11 SCR on link training.)
+ */
+static bool
+intel_dp_128b132b_link_train(struct intel_dp *intel_dp,
+ const struct intel_crtc_state *crtc_state,
+ int lttpr_count)
+{
+ struct drm_i915_private *i915 = dp_to_i915(intel_dp);
+ struct intel_connector *connector = intel_dp->attached_connector;
+ struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
+ bool passed = false;
+ u8 sink_status;
+
+ /* FIXME: We should possibly do this earlier. */
+ if (drm_dp_dpcd_readb(&intel_dp->aux, DP_SINK_STATUS, &sink_status) != 1) {
+ drm_dbg_kms(&i915->drm, "Failed to read sink status\n");
+ return false;
+ }
+
+ if (sink_status & DP_INTRA_HOP_AUX_REPLY_INDICATION) {
+ drm_dbg_kms(&i915->drm, "Previous link training in progress\n");
+ return false;
+ }
+
+ if (intel_dp_128b132b_lane_eq(intel_dp, crtc_state) &&
+ intel_dp_128b132b_lane_cds(intel_dp, crtc_state, lttpr_count))
+ passed = true;
+
+ drm_dbg_kms(&i915->drm,
+ "[CONNECTOR:%d:%s][ENCODER:%d:%s] 128b/132b Link Training %s at link rate = %d, lane count = %d\n",
+ connector->base.base.id, connector->base.name,
+ encoder->base.base.id, encoder->base.name,
+ passed ? "passed" : "failed",
+ crtc_state->port_clock, crtc_state->lane_count);
+
+ return passed;
+}
+
/**
* intel_dp_start_link_train - start link training
* @intel_dp: DP struct
@@ -1115,6 +1386,7 @@ intel_dp_link_train_all_phys(struct intel_dp *intel_dp,
void intel_dp_start_link_train(struct intel_dp *intel_dp,
const struct intel_crtc_state *crtc_state)
{
+ static bool passed;
/*
* TODO: Reiniting LTTPRs here won't be needed once proper connector
* HW state readout is added.
@@ -1127,6 +1399,11 @@ void intel_dp_start_link_train(struct intel_dp *intel_dp,

intel_dp_prepare_link_train(intel_dp, crtc_state);

- if (!intel_dp_link_train_all_phys(intel_dp, crtc_state, lttpr_count))
+ if (intel_dp_is_uhbr(crtc_state))
+ passed = intel_dp_128b132b_link_train(intel_dp, crtc_state, lttpr_count);
+ else
+ passed = intel_dp_link_train_all_phys(intel_dp, crtc_state, lttpr_count);
+
+ if (!passed)
intel_dp_schedule_fallback_link_training(intel_dp, crtc_state);
}
--
2.30.2