drm/i915/dp: rewrite DP 2.0 128b/132b link training based on errata

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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.

v4:
- Wait for intra-hop clear after link training end (Ville)
- Wait instead of single check for intra-hop clear before link train

v3:
- Use msecs_to_jiffies_timeout() (Ville)
- Read status at the beginning of interlane align done loop (Ville)
- Try to simplify timeout flag use where possible (Ville)

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>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220208143209.2997337-1-jani.nikula@intel.com

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This commit is contained in:

Jani Nikula 2022-02-08 16:32:09 +02:00

parent 92e438619d

commit a421d8a992

1 changed files with 300 additions and 1 deletions

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

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