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:

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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;
}