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https://bugs.launchpad.net/bugs/1744638

Title:
  [Bug] [CNL] mei: LTR holds platform at Pkg C2, cannot enter deeper Pkg
  C states

Status in intel:
  Fix Released
Status in linux package in Ubuntu:
  Fix Released
Status in linux source package in Bionic:
  Fix Released

Bug description:
  Description:
  Platform: CNL-Y8 LPDDR4 PI (merged rail) RVP with BIOS 108

  BIOS configuration: 
https://wiki.ith.intel.com/pages/viewpage.action?pageId=865050787
  At least as far back as the 2017-10-25 Intel Next merge, platform will not go 
deeper than Pkg C2 when system is idle. Upon further debug, using the pmc_core 
driver to ignore LTR "6", or bit 6 of LTR_IGN, can allow the system can enter 
Pkg C8.

  If I'm not mistaken, according to CSpec bit 6 of LTR_IGN will ignore
  LTR_ME, which is in the MEI driver's domain.

  Reproduce by:

  Boot to text console with latest Intel Next kernel (2017-10-30 as of writing)
  Run turbostat
  See residency no deeper than Pkg C2
  Expected:
  At idle, system shows nonzero Pkg C8 residency, or deeper.

  Actual:
  At idle, system only shows nonzero Pkg C2 residency.

  Two work-arounds:

  echo 6 > /sys/kernel/debug/pmc_core/ltr_ignore
  Run powertop --auto-tune
  Criteria for closure:

  Idle system can enter Pkg C8 (or deeper) without having to explicitly
  "ignore" LTR 6 or otherwise have to manually enable runtime power
  management for MEI device(s).

  Commit ids:
  Upstream commit, planned to be merged into 4.16

  commit cc365dcf0e56271bedf3de95f88922abe248e951
  Author: Tomas Winkler <tomas.wink...@intel.com>
  Date: Tue Jan 2 12:01:41 2018 +0200

  mei: me: allow runtime pm for platform with D0i3

  Target Kernel: 4.16
  Target Release: 18.04

  break-fix: - cc365dcf0e56271bedf3de95f88922abe248e951

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