[PATCH 2/5] usb: assign ACPI companions for embedded USB devices

[Rajat Jain]

From: Dmitry Torokhov <dtor@xxxxxxxxxxxx>

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-devices

Signed-off-by: Dmitry Torokhov <dtor@xxxxxxxxxxxx>
Signed-off-by: Rajat Jain <rajatja@xxxxxxxxxx> (changed how we get the usb_port)
---
 drivers/usb/core/usb-acpi.c | 44 +++++++++++++++++++++++++++++--------
 1 file changed, 35 insertions(+), 9 deletions(-)

diff --git a/drivers/usb/core/usb-acpi.c b/drivers/usb/core/usb-acpi.c
index 8ff73c83e8e8..9043d7242d67 100644
--- a/drivers/usb/core/usb-acpi.c
+++ b/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));
-- 
2.19.1.1215.g8438c0b245-goog