drm/i915: Switch to LTTPR non-transparent mode link training

The DP Standard's recommendation is to use the LTTPR non-transparent
mode link training if LTTPRs are detected, so let's do this.

Besides power-saving, the advantages of this are that the maximum number
of LTTPRs can only be used in non-transparent mode (the limit is 5-8 in
transparent mode), and it provides a way to narrow down the reason for a
link training failure to a given link segment. Non-transparent mode is
probably also the mode that was tested the most by the industry.

The changes in this patchset:
- Pass the DP PHY that is currently link trained to all LT helpers, so
  that these can access the correct LTTPR/DPRX DPCD registers.
- During LT take into account the LTTPR common lane rate/count and the
  per LTTPR-PHY vswing/pre-emph limits.
- Switch to LTTPR non-transparent LT mode and train each link segment
  according to the sequence in DP Standard v2.0 (complete CR/EQ for
  each segment before continuing with the next segment).

v2:
- Switch to non-transparent mode during connector detection, which is
  required before reading the per-PHY LTTPR capabilities.
- Move the DP_PHY_LTTPR() macro to drm_dp_helper.h (Ville)
- Use the new drm_dp_dpcd_read_phy_link_status() instead of adding the
  same logic to intel_dp_get_link_status(). (Ville)
- Make intel_dp_lttpr_phy_caps() return a pointer to the whole array
  instead of a pointer to its first element. (Ville)
- Add the intel_dp_phy_is_downstream_of_source() helper. (Ville)
- Add a code comment about the disable->enable quirk of
  non-transparent mode.
- Add the intel_dp_training_pattern_set_reg() helper.
- Fix checkpatch/sparse warns.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201007170917.1764556-7-imre.deak@intel.com

Author: ideak

drivers/gpu/drm/i915/display/intel_display_types.h

@@ -1303,6 +1303,7 @@ struct intel_dp {
 	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 lttpr_phy_caps[DP_MAX_LTTPR_COUNT][DP_LTTPR_PHY_CAP_SIZE];
 	u8 fec_capable;
 	/* source rates */
 	int num_source_rates;

drivers/gpu/drm/i915/display/intel_dp.c

@@ -160,6 +160,7 @@ static void intel_dp_set_sink_rates(struct intel_dp *intel_dp)
 		162000, 270000, 540000, 810000
 	};
 	int i, max_rate;
+	int max_lttpr_rate;
 
 	if (drm_dp_has_quirk(&intel_dp->desc, 0,
 			     DP_DPCD_QUIRK_CAN_DO_MAX_LINK_RATE_3_24_GBPS)) {
@@ -173,6 +174,9 @@ static void intel_dp_set_sink_rates(struct intel_dp *intel_dp)
 	}
 
 	max_rate = drm_dp_bw_code_to_link_rate(intel_dp->dpcd[DP_MAX_LINK_RATE]);
+	max_lttpr_rate = drm_dp_lttpr_max_link_rate(intel_dp->lttpr_common_caps);
+	if (max_lttpr_rate)
+		max_rate = min(max_rate, max_lttpr_rate);
 
 	for (i = 0; i < ARRAY_SIZE(dp_rates); i++) {
 		if (dp_rates[i] > max_rate)
@@ -218,6 +222,10 @@ static int intel_dp_max_common_lane_count(struct intel_dp *intel_dp)
 	int source_max = dig_port->max_lanes;
 	int sink_max = drm_dp_max_lane_count(intel_dp->dpcd);
 	int fia_max = intel_tc_port_fia_max_lane_count(dig_port);
+	int lttpr_max = drm_dp_lttpr_max_lane_count(intel_dp->lttpr_common_caps);
+
+	if (lttpr_max)
+		sink_max = min(sink_max, lttpr_max);
 
 	return min3(source_max, sink_max, fia_max);
 }
@@ -4179,17 +4187,6 @@ static void chv_dp_post_pll_disable(struct intel_atomic_state *state,
 	chv_phy_post_pll_disable(encoder, old_crtc_state);
 }
 
-/*
- * Fetch AUX CH registers 0x202 - 0x207 which contain
- * link status information
- */
-bool
-intel_dp_get_link_status(struct intel_dp *intel_dp, u8 link_status[DP_LINK_STATUS_SIZE])
-{
-	return drm_dp_dpcd_read(&intel_dp->aux, DP_LANE0_1_STATUS, link_status,
-				DP_LINK_STATUS_SIZE) == DP_LINK_STATUS_SIZE;
-}
-
 static u8 intel_dp_voltage_max_2(struct intel_dp *intel_dp,
 				 const struct intel_crtc_state *crtc_state)
 {
@@ -5592,13 +5589,15 @@ static void intel_dp_process_phy_request(struct intel_dp *intel_dp,
 		&intel_dp->compliance.test_data.phytest;
 	u8 link_status[DP_LINK_STATUS_SIZE];
 
-	if (!intel_dp_get_link_status(intel_dp, link_status)) {
+	if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, DP_PHY_DPRX,
+					     link_status) < 0) {
 		DRM_DEBUG_KMS("failed to get link status\n");
 		return;
 	}
 
 	/* retrieve vswing & pre-emphasis setting */
-	intel_dp_get_adjust_train(intel_dp, crtc_state, link_status);
+	intel_dp_get_adjust_train(intel_dp, crtc_state, DP_PHY_DPRX,
+				  link_status);
 
 	intel_dp_autotest_phy_ddi_disable(intel_dp, crtc_state);
 
@@ -5756,7 +5755,8 @@ intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
 	if (intel_psr_enabled(intel_dp))
 		return false;
 
-	if (!intel_dp_get_link_status(intel_dp, link_status))
+	if (drm_dp_dpcd_read_phy_link_status(&intel_dp->aux, DP_PHY_DPRX,
+					     link_status) < 0)
 		return false;
 
 	/*

drivers/gpu/drm/i915/display/intel_dp.h

@@ -102,8 +102,6 @@ void intel_dp_compute_rate(struct intel_dp *intel_dp, int port_clock,
 			   u8 *link_bw, u8 *rate_select);
 bool intel_dp_source_supports_hbr2(struct intel_dp *intel_dp);
 bool intel_dp_source_supports_hbr3(struct intel_dp *intel_dp);
-bool
-intel_dp_get_link_status(struct intel_dp *intel_dp, u8 *link_status);
 
 bool intel_dp_get_colorimetry_status(struct intel_dp *intel_dp);
 int intel_dp_link_required(int pixel_clock, int bpp);