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  Power consumption during s2idle is higher than long idle(sk hynix)

Status in linux package in Ubuntu:
  Fix Committed
Status in linux source package in Bionic:
  Fix Committed
Status in linux source package in Cosmic:
  Fix Committed

Bug description:
  On some Dell XPS models, we observed the power consumption raises higher than 
long idle does during s2idle with sk hynix nvme.

  Short idle: 4
  Long idle: 1
  S2I: 3.7
  S5: 0.19

  Short idle: 7.2
  Long idle: 4.5
  S2I: 6.22
  S5: 0.18

  Short idle: 6.5
  Long idle: 1
  S2I: 2.88
  S5: 0.18

  From SK hynix FE, MS Windows doesn't put nvme to D3, and uses its own APST 
feature to do the power management. To leverage its APST feature during s2idle, 
we can't disable nvme device while suspending, too.
  So, here is what we did on the driver, 1. prevent nvme from entering D3, 2. 
prevent nvme from being disabled when suspending.

  Verified on different XPS machines with different sk hynix nvme disks, it 
fixes the power consumption issue with no regression. And the power consumption 
drops to 0.77W during s2idle.

  [Regression Potential]
  Low, the patches only applied to specific nvme module, and from our test, the 
system is still stable.

  This issue should be fixed by the firmware, and we're pushing sk hynix to fix 
it. But before sk hynix find out how to solve it, we have to preserve these 
commits in our kernel for a while.
  BTW, the patches use pm_suspend_via_s2idle() function from below commit which 
is still under reviewing.

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