On Wed, 26 Jan 2022, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> On Tue, Jan 25, 2022 at 07:03:43PM +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.
>>
>> Cc: Uma Shankar <uma.shankar@xxxxxxxxx>
>> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
>> ---
>> .../drm/i915/display/intel_dp_link_training.c | 252 +++++++++++++++++-
>> 1 file changed, 251 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..8bb6a296f421 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 +1102,250 @@ 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;
>> +
>> + /*
>> + * 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;
>> + }
>> +
>> + 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;
>> + }
>> +
>> + /* 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;
>> + }
>> +
>> + /*
>> + * FIXME: This should probably be the total time budget for the complete
>> + * LANEx_EQ_DONE Sequence, including the loop above and the aux rd
>> + * intervals.
>> + */
>
> That is what my spec reading skills tell me. I suspect it's just there
> to make sure some broken device can't specify an overly long aux rd
> interval and make the link training too long. 20*256ms=~5 seconds max.
>
> I'd either drop this for now, or try to intergrate properly inte loop.
Extended it over the entire sequence.
>
>> + deadline = jiffies + msecs_to_jiffies(400);
>> + 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 (time_after(jiffies, deadline)) {
>> + 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;
>> + }
>> +
>> + 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;
>> +
>> + 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;
>> + }
>> +
>> + 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_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 (time_after(jiffies, deadline)) {
>
> This is racy. There's no telling how much time has passed since
> the last time we checked the status. Standard rule of timeouts:
> always check one last time after the timeout has expired.
Right, thanks, fixed.
>
>> + 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;
>> + }
>> + }
>> +
>> + /* FIXME: Should DP_TRAINING_PATTERN_DISABLE be written first? */
>
> Not sure. The other thing missing is waiting for the intra-hop AUX
> indicator to go away after we exit link training.
Hum, I guess I've missed that. I thought we should check for that before
we start. (And yes, that's missing, there's another FIXME.)
>
> It seems we should also block all other aux transfers during LT
> because of the intra-hop AUX mode. I can imagine things might get
> a bit confused if the LTTPRs start answering directly to AUX
> transfers that are intended to pass through to the DPRX.
Yeah, I've left that for the future. I haven't figured out a clean way
to do it yet.
>
>> + 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 intel_connector *connector = intel_dp->attached_connector;
>> + struct intel_encoder *encoder = &dp_to_dig_port(intel_dp)->base;
>> + bool passed = false;
>> +
>> + /*
>> + * FIXME: Validate previous LT termination by reading Intra-Hop AUX
>> + * Reply Indication by reading bit 3 of SINK_STATUS at 00205h
>> + */
>> +
>> + 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(&dp_to_i915(intel_dp)->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 +1359,7 @@ 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 +1372,11 @@ 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
--
Jani Nikula, Intel Open Source Graphics Center
