usb: assign ACPI companions for embedded USB devices

USB devices permanently connected to USB ports may be described in ACPI
tables and share ACPI devices with ports they are connected to. See [1]
for details.

This will allow us to describe sideband resources for devices, such as,
for example, hard reset line for BT USB controllers.

[1] https://docs.microsoft.com/en-us/windows-hardware/drivers/bringup/other-acpi-namespace-objects#acpi-namespace-hierarchy-and-adr-for-embedded-usb-devicesSigned-off-by: Dmitry Torokhov <dtor@chromium.org>
Signed-off-by: Rajat Jain <rajatja@google.com> (changed how we get the usb_port)
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Tested-by: Sukumar Ghorai <sukumar.ghorai@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

drivers/usb/core/usb-acpi.c

@@ -200,30 +200,56 @@ static struct acpi_device *
 usb_acpi_find_companion_for_device(struct usb_device *udev)
 {
 	struct acpi_device *adev;
+	struct usb_port *port_dev;
+	struct usb_hub *hub;
+
+	if (!udev->parent) {
+		/* root hub is only child (_ADR=0) under its parent, the HC */
+		adev = ACPI_COMPANION(udev->dev.parent);
+		return acpi_find_child_device(adev, 0, false);
+	}
 
-	if (!udev->parent)
+	hub = usb_hub_to_struct_hub(udev->parent);
+	if (!hub)
 		return NULL;
 
-	/* root hub is only child (_ADR=0) under its parent, the HC */
-	adev = ACPI_COMPANION(udev->dev.parent);
-	return acpi_find_child_device(adev, 0, false);
+	/*
+	 * This is an embedded USB device connected to a port and such
+	 * devices share port's ACPI companion.
+	 */
+	port_dev = hub->ports[udev->portnum - 1];
+	return usb_acpi_get_companion_for_port(port_dev);
 }
 
-
 static struct acpi_device *usb_acpi_find_companion(struct device *dev)
 {
 	/*
-	 * In the ACPI DSDT table, only usb root hub and usb ports are
-	 * acpi device nodes. The hierarchy like following.
+	 * The USB hierarchy like following:
+	 *
 	 * Device (EHC1)
 	 *	Device (HUBN)
 	 *		Device (PR01)
 	 *			Device (PR11)
 	 *			Device (PR12)
+	 *				Device (FN12)
+	 *				Device (FN13)
 	 *			Device (PR13)
 	 *			...
-	 * So all binding process is divided into two parts. binding
-	 * root hub and usb ports.
+	 * where HUBN is root hub, and PRNN are USB ports and devices
+	 * connected to them, and FNNN are individualk functions for
+	 * connected composite USB devices. PRNN and FNNN may contain
+	 * _CRS and other methods describing sideband resources for
+	 * the connected device.
+	 *
+	 * On the kernel side both root hub and embedded USB devices are
+	 * represented as instances of usb_device structure, and ports
+	 * are represented as usb_port structures, so the whole process
+	 * is split into 2 parts: finding companions for devices and
+	 * finding companions for ports.
+	 *
+	 * Note that we do not handle individual functions of composite
+	 * devices yet, for that we would need to assign companions to
+	 * devices corresponding to USB interfaces.
 	 */
 	if (is_usb_device(dev))
 		return usb_acpi_find_companion_for_device(to_usb_device(dev));