1. 20 Oct, 2021 1 commit
    • Imre Deak's avatar
      drm/i915/dp: Skip the HW readout of DPCD on disabled encoders · 4ec5ffc3
      Imre Deak authored
      Reading out the DP encoders' DPCD during booting or resume is only
      required for enabled encoders: such encoders may be modesetted during
      the initial commit and the link training this involves depends on an
      initialized DPCD. For DDI encoders reading out the DPCD is skipped, do
      the same on pre-DDI platforms.
      
      Atm, the first DPCD readout without a sink connected - which is a likely
      scneario if the encoder is disabled - leaves intel_dp->num_common_rates
      at 0, which resulted in
      
      intel_dp_sync_state()->intel_dp_max_common_rate()
      
      in a
      
      intel_dp->common_rates[-1]
      
      access. This by definition results in an undefined behaviour, though to
      my best knowledge in all HW/compiler configurations it actually results
      in accessing the array item type value preceding the array. In this
      case the preceding value happens to be intel_dp->num_common_rates,
      which is 0, so this issue - by luck - didn't cause a user visible
      problem.
      
      Nevertheless it's still an undefined behaviour and in CONFIG_UBSAN
      builds leads to a kernel BUG() (which revealed this problem for us),
      hence CC:stable.
      
      A related problem in case the encoder is enabled but the sink is not
      connected or the DPCD readout fails is fixed by the next patch.
      
      v2: Amend the commit message describing the root cause of the
          CONFIG_UBSAN BUG().
      
      Fixes: a532cde3 ("drm/i915/tc: Fix TypeC port init/resume time sanitization")
      References: https://gitlab.freedesktop.org/drm/intel/-/issues/4297Reported-and-tested-by: default avatarMat Jonczyk <mat.jonczyk@o2.pl>
      Cc: Mat Jonczyk <mat.jonczyk@o2.pl>
      Cc: José Roberto de Souza <jose.souza@intel.com>
      Cc: Jani Nikula <jani.nikula@intel.com>
      Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
      Cc: <stable@vger.kernel.org>
      Signed-off-by: default avatarImre Deak <imre.deak@intel.com>
      Reviewed-by: default avatarVille Syrjälä <ville.syrjala@linux.intel.com>
      Acked-by: default avatarJani Nikula <jani.nikula@intel.com>
      Link: https://patchwork.freedesktop.org/patch/msgid/20211018094154.1407705-2-imre.deak@intel.com
      4ec5ffc3
  2. 19 Oct, 2021 13 commits
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