PCI / ACPI: Whitelist D3 for more PCIe hotplug ports

In order to have better power management for Thunderbolt PCIe chains,
Windows enables power management for native PCIe hotplug ports if there is
the following ACPI _DSD attached to the root port:

  Name (_DSD, Package () {
      ToUUID ("6211e2c0-58a3-4af3-90e1-927a4e0c55a4"),
      Package () {
          Package () {"HotPlugSupportInD3", 1}
      }
  })

This is also documented in:

  https://docs.microsoft.com/en-us/windows-hardware/drivers/pci/dsd-for-pcie-root-ports#identifying-pcie-root-ports-supporting-hot-plug-in-d3

Do the same in Linux by introducing new firmware PM callback
(->bridge_d3()) and then implement it for ACPI based systems so that the
above property is checked.

There is one catch, though. The initial pci_dev->bridge_d3 is set before
the root port has ACPI companion bound (the device is not added to the PCI
bus either) so we need to look up the ACPI companion manually in that case
in acpi_pci_bridge_d3().

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/drivers/pci/pci-acpi.c b/drivers/pci/pci-acpi.c
index f8436d1c4d45..c8d0549580f4 100644
--- a/drivers/pci/pci-acpi.c
+++ b/drivers/pci/pci-acpi.c
@@ -519,6 +519,46 @@ static pci_power_t acpi_pci_choose_state(struct pci_dev *pdev)
 	return PCI_POWER_ERROR;
 }
 
+static struct acpi_device *acpi_pci_find_companion(struct device *dev);
+
+static bool acpi_pci_bridge_d3(struct pci_dev *dev)
+{
+	const struct fwnode_handle *fwnode;
+	struct acpi_device *adev;
+	struct pci_dev *root;
+	u8 val;
+
+	if (!dev->is_hotplug_bridge)
+		return false;
+
+	/*
+	 * Look for a special _DSD property for the root port and if it
+	 * is set we know the hierarchy behind it supports D3 just fine.
+	 */
+	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;
+
+	fwnode = acpi_fwnode_handle(adev);
+	if (fwnode_property_read_u8(fwnode, "HotPlugSupportInD3", &val))
+		return false;
+
+	return val == 1;
+}
+
 static bool acpi_pci_power_manageable(struct pci_dev *dev)
 {
 	struct acpi_device *adev = ACPI_COMPANION(&dev->dev);
@@ -635,6 +675,7 @@ static bool acpi_pci_need_resume(struct pci_dev *dev)
 }
 
 static const struct pci_platform_pm_ops acpi_pci_platform_pm = {
+	.bridge_d3 = acpi_pci_bridge_d3,
 	.is_manageable = acpi_pci_power_manageable,
 	.set_state = acpi_pci_set_power_state,
 	.get_state = acpi_pci_get_power_state,