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    • Imre Deak's avatar
      drm/i915/dp: Add workaround for spurious AUX timeouts/hotplugs on LTTPR links · eddbb074
      Imre Deak authored
      
      
      To avoid AUX timeouts and subsequent spurious hotplug interrupts, make
      sure that the first DPCD access during detection is a read from an LTTPR
      register.
      
      Some ADLP DP link configuration at least with multiple LTTPRs expects
      the first DPCD access during the LTTPR/DPCD detection after hotplug to
      be a read from the LTTPR range starting with
      DP_LT_TUNABLE_PHY_REPEATER_FIELD_DATA_STRUCTURE_REV. The side effect of
      this read is to put each LTTPR into the LTTPR transparent or LTTPR
      non-transparent mode.
      
      The lack of the above read may leave some of the LTTPRs in non-LTTPR
      mode, while other LTTPRs in LTTPR transparent or LTTPR non-transparent
      mode (for instance LTTPRs after system suspend/resume that kept their
      mode from before suspend). Due to the different AUX timeouts the
      different modes imply, the DPCD access from a non-LTTPR range will
      timeout and lead to an LTTPR generated hotplug towards the source (which
      the LTTPR firmware uses to account for buggy TypeC adapters with a long
      wake-up delay).
      
      SYSCROS: 72939
      
      v2: Keep DPCD read-out working on non-LTTPR platforms.
      v3: Summarize what and why the patch does at the beginning of the commit
          log. (Jani)
      
      Signed-off-by: default avatarImre Deak <imre.deak@intel.com>
      Reviewed-by: default avatarJani Nikula <jani.nikula@intel.com>
      Link: https://patchwork.freedesktop.org/patch/msgid/20220408224629.845887-1-imre.deak@intel.com
      eddbb074
  13. Apr 26, 2022