linux-kernel - Re: [PATCH] nvme/pci: Use host managed power state for suspend

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Date:   Mon, 13 May 2019 16:54:15 +0200
From:   Christoph Hellwig <hch@....de>
To:     Mario.Limonciello@...l.com
Cc:     hch@....de, keith.busch@...el.com, sagi@...mberg.me,
        linux-nvme@...ts.infradead.org, rafael@...nel.org,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        kai.heng.feng@...onical.com
Subject: Re: [PATCH] nvme/pci: Use host managed power state for suspend

On Mon, May 13, 2019 at 02:43:43PM +0000, Mario.Limonciello@...l.com wrote:
> Well I've got a thought, quoting the NVME spec:
> "After a successful completion of a Set Features command for this feature, the controller shall be in the
> Power State specified. If enabled, autonomous power state transitions continue to occur from the new state."
> 
> If APST is enabled on this disk, what is to stop an autonomous  reverse
> transition from queue activity on the way down?

Nothing.  But once the system is suspending we should not see I/O.

If we see I/O the queue freezing in the original patch Kai Heng and the
previous one from Keith is probably required, although I suspect it
just papers over problems higher up in the queue.  If we don't see I/O
the device is just behaving oddly.