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Re: [PATCH 0/5] nvme APST fixes/improvements for 4.11

On Wed, Apr 19 2017, Andy Lutomirski wrote:
> Sorry for waiting so long for this.  I was waiting for feedback from
> Samsung, but they haven't root-caused the issue yet, and I should
> have just done this from the beginning.
> This series makes APST more debuggable and updates the quirk list.
> The quirks I'm aware of are:
>  - Samsung 950 series SSDs in Dell XPS 15 9550 and Precision 5510
>    laptops (which are essentially the same laptop) can lose their
>    PCIe link if they're allowed to use the deepest APST state.
>    Samsung engineers have an affected system and are working on
>    it.  The same exact SSDs in other machines (even an XPS 13)
>    seem to work fine.
>  - One Toshiba device malfunctions if APST is used at all.

You need to split this series in two, patches 1-3 can wait. For 4.11,
all we need to do is turn off APST on any device that potentially has
this problem.

> One thing that improves my confidence that there aren't too many
> more problems with APST is that Ubuntu has backported APST to Zesty,
> so it's already gotten a bit of testing in a widely used (if very
> new) release.

Honestly, I think the best path for 4.11 is to turn off APST by default,
make it opt-in instead. I don't share your optimism here, as I made
clear back from before we even merged this feature.

Jens Axboe