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** Changed in: linux (Ubuntu)
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/1759547

Title:
  Use med_with_dipm SATA LPM to save more power for mobile platforms

Status in linux package in Ubuntu:
  Incomplete

Bug description:
  In order to let CPU Package gets deeper C-state, we need to use power-
  saving SATA LPM to achieve that.

  This commit introduce a new config, SATA_MOBILE_LPM_POLICY:

  commit ebb82e3c79d2a956366d0848304a53648bd6350b
  Author: Hans de Goede <[email protected]>
  Date:   Mon Dec 11 17:52:16 2017 +0100

      ahci: Allow setting a default LPM policy for mobile chipsets

      On many laptops setting a different LPM policy then unknown /
      max_performance can lead to power-savings of 1.0 - 1.5 Watts (when idle).

      Modern ultrabooks idle around 6W (at 50% screen brightness), 1.0 - 1.5W
      is a significant chunk of this.

      There are some performance / latency costs to enabling LPM by default,
      so it is desirable to make it possible to set a different LPM policy
      for mobile / laptop variants of chipsets / "South Bridges" vs their
      desktop / server counterparts. Also enabling LPM by default is not
      entirely without risk of regressions. At least min_power is known to
      cause issues with some disks, including some reports of data corruption.

      This commits adds a new ahci.mobile_lpm_policy kernel cmdline option,
      which defaults to a new SATA_MOBILE_LPM_POLICY Kconfig option so that
      Linux distributions can choose to set a LPM policy for mobile chipsets
      by default.

      The reason to have both a kernel cmdline option and a Kconfig default
      value for it, is to allow easy overriding of the default to allow
      trouble-shooting without needing to rebuild the kernel.

      Signed-off-by: Hans de Goede <[email protected]>
      Signed-off-by: Tejun Heo <[email protected]>

  "3 => Medium power with Device Initiated PM enable" is a well-balanced
  that can let Package enters deeper C-state.

  Also, Fedora already set SATA_MOBILE_LPM_POLICY=3 for their latest
  kernel.

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