linux-kernel - Re: [PATCH 0/2] Add support for StorageD3Enable

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Message-ID: <de2d78556fcb10f97364201256ac8f342a58eb75.camel@linux.intel.com>
Date:   Tue, 28 Apr 2020 08:27:50 -0700
From:   "David E. Box" <david.e.box@...ux.intel.com>
To:     Christoph Hellwig <hch@....de>
Cc:     rjw@...ysocki.net, lenb@...nel.org, bhelgaas@...gle.com,
        kbusch@...nel.org, axboe@...com, sagi@...mberg.me,
        linux-acpi@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Add support for StorageD3Enable _DSD property

On Tue, 2020-04-28 at 16:22 +0200, Christoph Hellwig wrote:
> On Tue, Apr 28, 2020 at 07:09:59AM -0700, David E. Box wrote:
> > > I'm not sure who came up with the idea to put this into ACPI, but
> > > it
> > > belongs into NVMe.  Please talk to the NVMe technical working
> > > group
> > > instead of trying to overrules them in an unrelated group that
> > > doesn't
> > > apply to all of PCIe.
> > 
> > Agreed that this is not ideal since it does not apply to all of
> > PCIe.
> > But as the property already exists on shipping systems, we need to
> > be
> > able to read it in the NVMe driver and the patch is consitent with
> > the
> > way properties under PCI ports are read.
> 
> The point is that it is not the BIOSes job do decide how Linux does
> power management.  For example D3 has really horrible entry and exit
> latencies in many cases, and will lead to higher power usage.

The platform can know which pm policies will save the most power. But
since the solution doesn't apply to all PCIe devices (despite BIOS
specifying it that way) I'll withdraw this patch. Thanks.

David