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SubjectRe: [PATCH 1/2] pci: Add ACPI StorageD3Enable _DSD support
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On Mon, 2020-05-18 at 14:34 +0200, Rafael J. Wysocki wrote:
> On Tuesday, April 28, 2020 2:32:13 AM CEST 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.
> >
> > Adds support for the _DSD to the pci/acpi layer.
> >
> > Acked-by: Dan Williams <dan.j.williams@intel.com>
> > Link:
> > https://docs.microsoft.com/en-us/windows-hardware/design/component-guidelines/power-management-for-storage-hardware-devices-intro
> > Signed-off-by: David E. Box <david.e.box@linux.intel.com>
> > ---
> > drivers/acpi/property.c | 3 +++
> > drivers/pci/pci-acpi.c | 47
> > +++++++++++++++++++++++++++++++++++++++++
> > drivers/pci/pci.c | 6 ++++++
> > drivers/pci/pci.h | 4 ++++
> > include/linux/pci.h | 1 +
> > 5 files changed, 61 insertions(+)
> >
> > diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> > index e601c4511a8b..f09375ab40e4 100644
> > --- a/drivers/acpi/property.c
> > +++ b/drivers/acpi/property.c
> > @@ -45,6 +45,9 @@ static const guid_t prp_guids[] = {
> > /* Thunderbolt GUID for WAKE_SUPPORTED: 6c501103-c189-4296-
> > ba72-9bf5a26ebe5d */
> > GUID_INIT(0x6c501103, 0xc189, 0x4296,
> > 0xba, 0x72, 0x9b, 0xf5, 0xa2, 0x6e, 0xbe, 0x5d),
> > + /* D3 Support for storage devivce: 5025030f-842f-4ab4-a561-
> > 99a5189762d0 */
> > + GUID_INIT(0x5025030f, 0x842f, 0x4ab4,
> > + 0xa5, 0x61, 0x99, 0xa5, 0x18, 0x97, 0x62, 0xd0),
> > };
> >
> > /* ACPI _DSD data subnodes GUID: dbb8e3e6-5886-4ba6-8795-
> > 1319f52a966b */
> > diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> > index d21969fba6ab..5df249ebf022 100644
> > --- a/drivers/pci/pci-acpi.c
> > +++ b/drivers/pci/pci-acpi.c
> > @@ -972,6 +972,52 @@ static bool acpi_pci_bridge_d3(struct pci_dev
> > *dev)
> > return val == 1;
> > }
> >
> > +static bool acpi_pci_storage_d3(struct pci_dev *dev)
> > +{
> > + const struct fwnode_handle *fwnode;
> > + struct acpi_device *adev;
> > + struct pci_dev *root;
> > + acpi_handle handle;
> > + acpi_status status;
> > + u8 val;
> > +
> > + /*
> > + * Look for _DSD property specifying that the storage device on
> > + * the port must use D3 to support deep platform power savings
> > during
> > + * suspend-to-idle
> > + */
> > + root = pci_find_pcie_root_port(dev);
> > + if (!root)
> > + return false;
> > +
> > + adev = ACPI_COMPANION(&root->dev);
> > + if (root == dev) {
> > + /*
> > + * It is possible that the ACPI companion is not yet
> > bound
> > + * for the root port so look it up manually here.
> > + */
> > + if (!adev && !pci_dev_is_added(root))
> > + adev = acpi_pci_find_companion(&root->dev);
> > + }
> > +
> > + if (!adev)
> > + return false;
> > +
> > + status = acpi_get_handle(adev->handle, "PXSX", &handle);
> > + if (ACPI_FAILURE(status))
> > + return false;
> > +
> > + adev = acpi_bus_get_acpi_device(handle);
> > + if (!adev)
> > + return false;
> > +
> > + fwnode = acpi_fwnode_handle(adev);
> > + if (!fwnode_property_read_u8(fwnode, "StorageD3Enable", &val))
> > + return val == 1;
> > +
> > + return false;
> > +}
>
> Kind of orthogonal to what happens to the second patch in this
> series, I don't
> think that the PCI changes below are all needed.
>
> IMO it would be sufficient to export the function above, maybe as
> pci_acpi_storage_d3(), to drivers, so that they can call it directly
> as
> desired.
>
> Since _DSD return data are not allowed by the spec to change between
> subsequent invocations of it, the interested driver may call this
> function
> once at the device init time and quirk it accordingly if needed.

Yeah this is better. Will do. Thanks.

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