[PATCH 1/4] USB: ACPI: Look for `usb4-host-interface` property

[Mario Limonciello <mario.limonciello@amd.com>]

For optimal power consumption of USB4 routers the XHCI PCIe endpoint
used for tunneling must be in D3.  Historically this is accomplished
by a long list of PCIe IDs that correspond to these endpoints.

The linux thunderbolt CM currently uses the `usb4-host-interface` ACPI
property to create a device link between the USB4 host router PCIe
endpoint and the XHCI PCIe endpoint.  The device link will move
the devices in out of D3 together.

To avoid having to maintain this never ending list of PCIe IDs, use
the existence of `usb4-host-interface` property on a USB port as a
proxy to allow runtime PM for these controllers.  The device links
will continue to be created when the CM initializes the USB4
host router and also discovers this property.

Link: https://learn.microsoft.com/en-us/windows-hardware/design/component-guidelines/usb4-acpi-requirements#port-mapping-_dsd-for-usb-3x-and-pcie
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
---
RFC v1->PATCH v1
 * Move this detection from Thunderbolt CM into USB core
---
 drivers/usb/core/usb-acpi.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/usb/core/usb-acpi.c b/drivers/usb/core/usb-acpi.c
index 6d93428432f13..f91ab4fd84cf8 100644
--- a/drivers/usb/core/usb-acpi.c
+++ b/drivers/usb/core/usb-acpi.c
@@ -177,6 +177,15 @@ usb_acpi_find_companion_for_port(struct usb_port *port_dev)
 		port_dev->connect_type = usb_acpi_get_connect_type(handle, pld);
 		ACPI_FREE(pld);
 	}
+	if (!acpi_dev_get_property(adev, "usb4-host-interface",
+				   ACPI_TYPE_ANY, NULL)) {
+		struct device *dev = &port_dev->dev;
+
+		while (dev && !dev_is_pci(dev))
+			dev = dev->parent;
+		if (dev)
+			pm_runtime_allow(dev);
+	}
 
 	return adev;
 }
-- 
2.34.1