NVMe APST on XPS 9550/Precison 5510

[Mario.Limonciello at dell.com]

Kai Heng,

>Hi Andy,
>The new quirk [1] in your nvme/power branch Mario pointd to me disables APST completely, but three different users reported that the NVMe works fine if the deepest state it enters is PS3 (comment #17, #18 and #19).
>So instead of not enabling APST, can we have a quirk to target specific power state? Users can still get nice powersaving without dead NVMe this way.
>Also, another user has the same issue on Lenovo ThinkPad X270 (comment #11 and #13), it uses Toshiba NVMe instead of Samsung.
>
>[1] https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=nvme/power&id=37294ae0e942e9dc56e869af23cc6face284dec8

Presumably you're referring to this bug? https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1678184

That's some interesting data points that you have found to share with other machines and drive combinations with problems as well
as limiting the deepest state to enter.

More and more people will be testing this since Ubuntu 17.04 is out with this patch included.  
At least until the problems related to PS4 being entered are properly root caused on the affected combinations, I wonder if it would 
be better to default to the more widely safe PS3 and whitelist combinations that PS4 is safe?