linux-kernel - Re: [PATCH] nvme-pci: Avoid to go into d3cold if device can't use npss.

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Date:   Thu, 27 May 2021 20:08:19 +0800
From:   Kai-Heng Feng <kai.heng.feng@...onical.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Bjorn Helgaas <helgaas@...nel.org>,
        Keith Busch <kbusch@...nel.org>,
        Koba Ko <koba.ko@...onical.com>, Jens Axboe <axboe@...com>,
        Sagi Grimberg <sagi@...mberg.me>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Henrik Juul Hansen <hjhansen2020@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux PCI <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] nvme-pci: Avoid to go into d3cold if device can't use npss.

On Thu, May 27, 2021 at 7:40 PM Christoph Hellwig <hch@....de> wrote:
>
> On Thu, May 27, 2021 at 12:24:06AM +0800, Kai-Heng Feng wrote:
> > Yes, that's exactly what they said. Because Windows Modern Standby
> > always keep the NVMe at D0, so D3hot is untested by the vendors.
>
> So all the problems we've deal with latetly are that platforms cut the
> power off.  So it is not kept always at D0 which would be the right thing,
> but moved into D3cold.

It's still okay to use D3cold under s2idle if nvme_acpi_storage_d3()
check passes.

Otherwise D0 should be used. I am unsure how to proceed with HMB NVMes
if we can't setup DMA after resume...

>
> Which makes this patch to disable D3cold rather counterintuitive.

The intention of this patch is indeed very unclear.

Kai-Heng