by Bjorn Helgaas

[permalink] [raw]

Subject: Re: [PATCH v15 7/9] PCI: Setup ACPI fwnode early and at the same time with OF

On Sat, Aug 14, 2021 at 11:16:11AM -0500, Shanker R Donthineni wrote:
> Hi Bjorn,
>
> On 8/13/21 11:10 PM, Bjorn Helgaas wrote:
> >>>> diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
> >>>> index eaddbf701759..dae021322b3f 100644
> >>>> --- a/drivers/pci/pci-acpi.c
> >>>> +++ b/drivers/pci/pci-acpi.c
> >>>> @@ -952,7 +952,6 @@ static bool acpi_pci_bridge_d3(struct pci_dev *dev)
> >>>> return false;
> >>>>
> >>>> /* Assume D3 support if the bridge is power-manageable by ACPI. */
> >>>> - pci_set_acpi_fwnode(dev);
> >>>> adev = ACPI_COMPANION(&dev->dev);
> >>> I *think* the Root Port code farther down in this function is also now
> >>> unnecessary:
> >>>
> >>> acpi_pci_bridge_d3(...)
> >>> {
> >>> ...
> >>> root = pcie_find_root_port(dev);
> >>> 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);
> >>> }
> >>>
> >>> Since we're now setting the ACPI_COMPANION for every pci_dev long
> >>> before we get here, I think this could now be simplified to something
> >>> like this:
> >>>
> >>> acpi_pci_bridge_d3(...)
> >>> {
> >>> if (!dev->is_hotplug_bridge)
> >>> return false;
> >>>
> >>> adev = ACPI_COMPANION(&dev->dev);
> >>> if (adev && acpi_device_power_manageable(adev))
> >>> return true;
> >>>
> >>> root = pcie_find_root_port(dev);
> >>> if (!root)
> >>> return false;
> >>>
> >>> adev = ACPI_COMPANION(&root->dev);
> >>> if (!adev)
> >>> return false;
> >>>
> >>> rc = acpi_dev_get_property(dev, "HotPlugSupportInD3",
> >>> ACPI_TYPE_INTEGER, &val);
> >>> if (rc < 0)
> >>> return false;
> >>>
> >>> return val == 1;
> >>> }
> >> Agree, thanks for your suggestion. Yes, it can be simplified too.
> >> Can I do something like this using the unified device property API?
> >>
> >> static bool acpi_pci_bridge_d3(struct pci_dev *dev)
> >> {
> >> struct acpi_device *adev;
> >> struct pci_dev *root;
> >> u8 val;
> >>
> >> if (!dev->is_hotplug_bridge)
> >> return false;
> >>
> >> adev = ACPI_COMPANION(&dev->dev);
> >> if (adev && acpi_device_power_manageable(adev))
> >> return true;
> >>
> >> root = pcie_find_root_port(dev);
> >> if (!root)
> >> return false;
> >>
> >> if (device_property_read_u8(&root->dev, "HotPlugSupportInD3", &val))
> >> return false;
> > I guess that might be OK.
> >
> > TBH I don't really like the device_property_read_u8() thing because
> > (1) we know this is an ACPI property and I don't see a reason to use
> > an "generic" interface that doesn't buy us anything, and (2) the
> > connection to the source of the data (a _DSD method) is really, really
> > hard to find.
> >
> > Admittedly, it's still pretty hard to connect acpi_dev_get_property()
> > with "_DSD". The only real clue is the comment about "Look for a
> > special _DSD property ..."
> >
> Does it satisfy you if I change the comment and still use device_property API?
>
> static bool acpi_pci_bridge_d3(struct pci_dev *dev)
> {
> ??????? struct pci_dev *rpdev;
> ??????? u8 val;
>
> ??????? if (!dev->is_hotplug_bridge)
> ??????????????? return false;
>
> ??????? /* Assume D3 support if the bridge is power-manageable by ACPI. */
> ??????? if (acpi_pci_power_manageable(dev))
> ??????????????? return true;
>
> ??????? /*
> ???????? * Look for 'HotPlugSupportInD3' property for the root port and if
> ???????? * it is set we know the hierarchy behind it supports D3 just fine.
> ???????? */
> ??????? rpdev = pcie_find_root_port(dev);
> ??????? if (!rpdev)
> ??????????????? return false;
>
> ??????? if (device_property_read_u8(&rpdev->dev, "HotPlugSupportInD3", &val))
> ??????????????? return false;
>
> ??????? return val == 1;
> }
>
> If not, I'll do changes like this.

I guess either one is fine. But I think we should extend the comment
and commit log to make it clear that device_property_read_u8() and
acpi_dev_get_property() are ultimately looking for a _DSD. I should
have asked for this when we merged 26ad34d510a8 ("PCI / ACPI:
Whitelist D3 for more PCIe hotplug ports") in the first place.

If we expect that power management *should* be enabled for a bridge,
and we observe that it *isn't* enabled, it is unreasonably difficult
to figure out from the code what is missing in the firmware, namely,
the _DSD laid out in the commit log for 26ad34d510a8.

> static bool acpi_pci_bridge_d3(struct pci_dev *dev)
> {
> ??????? const union acpi_object *obj;
> ??????? struct acpi_device *adev;
> ??????? struct pci_dev *rpdev;
>
>
> ??????? if (!dev->is_hotplug_bridge)
> ??????????????? return false;
>
> ??????? /* Assume D3 support if the bridge is power-manageable by ACPI. */
> ??????? if (acpi_pci_power_manageable(dev))
> ??????????????? return true;
>
> ??????? /*
> ???????? * Look for 'HotPlugSupportInD3' property for the root port and if
> ???????? * it is set we know the hierarchy behind it supports D3 just fine.
> ???????? */
> ??????? rpdev = pcie_find_root_port(dev);
> ??????? if (!rpdev)
> ??????????????? return false;
>
> ??????? adev = ACPI_COMPANION(&rpdev->dev);
> ??????? if (!adev)
> ??????????????? return false;
>
> ?????? if (acpi_dev_get_property(adev, "HotPlugSupportInD3",
> ?????????????????????????????????? ACPI_TYPE_INTEGER, &obj) < 0)
> ??????????????? return false;
>
> ??????? return obj->integer.value == 1;
> }
>
>