Re: [PATCH 0/2] Add support for StorageD3Enable _DSD property

[David E. Box]

On Tue, 2020-04-28 at 07:13 +0200, Christoph Hellwig wrote:
> On Mon, Apr 27, 2020 at 05:32:12PM -0700, David E. Box wrote:
> > NVMe storage power management during suspend-to-idle, particularly
> > on
> > laptops, has been inconsistent with some devices working with D3
> > while
> > others must rely on NVMe APST in order for power savings to be
> > realized.
> > Currently the default is to use APST unless quirked to do
> > otherwise.
> > However newer platforms, like Intel Comet Lake systems, may require
> > NVMe
> > drives to use D3 in order for the PCIe ports to be properly power
> > managed.
> > To make it easier for drivers to choose, these platforms may supply
> > a
> > special "StorageD3Enable" _DSD property under the root port that
> > the device
> > is attached to. If supplied, the driver must use D3 in order for
> > the
> > platform to realize the deepest power savings in suspend-to-idle.
> >     
> > The first patch adds the new _DSD GUID and fowards the property
> > through the
> > pci/acpi layer to the pci device.
> > 
> > The second patch adds support for the property to the nvme driver.
> 
> 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.

David