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Subject[PATCH v2 2/5] usb: assign ACPI companions for embedded USB devices
From
From: Dmitry Torokhov <dtor@chromium.org>

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@chromium.org>
Signed-off-by: Rajat Jain <rajatja@google.com> (changed how we get the usb_port)
---
v2: same as v1

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
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