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

On Thu, Feb 03, 2022 at 11:03:54AM +0200, Jani Nikula wrote:

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);

Didn't we have a msecs_to_jiffies_timeout() that adds an extra jiffy to make sure we don't bail too early?

• 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;
  

• }
  

The state diagrame has thow two steps in reverse order. I suppose it doens't matter but probably better if we don't deviate too much without a good reason.

• 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 */
  

Is there a reason we can't do this just before drm_dp_dpcd_read_link_status() so we don't have to pass the timeout status from one loop iteration to the next?

• /* 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;
  

• }
  

Not a big fan of pasing the link_status between loops. Can't we just read the status here at the start of the loop always?

• 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;
  

I think we are supposed to wait for the intra-hop AUX bit to go low here.

• 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