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

1 files changed, 1 insertions, 0 deletions

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 b3fb1d125b9b..86905aa24db7 100644
--- a/drivers/gpu/drm/i915/display/intel_dp_link_training.h
+++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.h
@@ -15,6 +15,7 @@ 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,
+			       enum drm_dp_phy dp_phy,
 			       const u8 link_status[DP_LINK_STATUS_SIZE]);
 void intel_dp_start_link_train(struct intel_dp *intel_dp,
 			       const struct intel_crtc_state *crtc_state);