Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 26 Jun 2017 11:05:32 -0700 | Subject | Re: [PATCH v2] nvme: explicitly disable APST on quirked devices |
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On Mon, Jun 26, 2017 at 12:01 AM, Kai-Heng Feng <kai.heng.feng@canonical.com> wrote: > A user reports APST is enabled, even when the NVMe is quirked or with > option "default_ps_max_latency_us=0". > > The current logic will not set APST if the device is quirked. But the > NVMe in question will enable APST automatically. > > Separate the logic "apst is supported" and "to enable apst", so we can > use the latter one to explicitly disable APST at initialiaztion.
Reviewed-by: Andy Lutomirski <luto@kernel.org>
That being said, I smell a giant WTF here. The affected hardware seems to have APST on by default, and APST is buggy so the disk stops working when APST is on. So here's the $1M question: how does the system *boot*? After all, it's running for a while before the kernel gets around to turning off APST, and I really doubt that BIOS does this.
Here's a wild theory: what if the problem on all these disks is actually our CSTS polling? Could it be that some of the disks implement CSTS reads in firmware and malfunction if CSTS is read while in PS4? This would be a blatant spec violation, but that's never stopped anyone before...
--Andy
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