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

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Date:   Mon, 13 May 2019 09:16:52 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Mario.Limonciello@...l.com, 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 04:57:08PM +0200, Christoph Hellwig wrote:
> On Mon, May 13, 2019 at 02:54:49PM +0000, Mario.Limonciello@...l.com wrote:
> > And NVME spec made it sound to me that while in a low power state it shouldn't
> > be available if the memory isn't available.
> > 
> > NVME spec in 8.9:
> > 
> > "Host software should request that the controller release the
> > assigned ranges prior to a shutdown event, a Runtime D3 event, or any other event
> > that requires host software to reclaim the assigned ranges."
> 
> The last part of the quoted text is the key - if the assigned range
> is reclaimed, that is the memory is going to be used for something else,
> we need to release the ranges.  But we do not release the ranges,
> as we want to keep the memory in use so that we can quickly use it
> again.

Yes, this. As far as I know, the host memory range is still accessible in
the idle suspend state. If there are states in which host memory is not
accessible, a reference explaining the requirement will be most helpful.