On Mon, 12 Mar 2012, Matthew Garrett wrote:
> Built-in USB devices will typically have a representation in the system
> ACPI tables. Add support for binding the two together so the USB code can
> make use of the associated methods.
> +static int usb_acpi_find_device(struct device *dev, acpi_handle *handle)
> +{
> + struct usb_device *udev = to_usb_device(dev);
> + struct device *parent = dev->parent;
> + acpi_handle *parent_handle = DEVICE_ACPI_HANDLE(parent);
> +
> + if (!parent_handle)
> + return -ENODEV;
> +
> + *handle = acpi_get_child(parent_handle, udev->portnum);
> +
> + if (!*handle)
> + return -ENODEV;
> +
> + return 0;
> +}
> +
> +static struct acpi_bus_type usb_acpi_bus = {
> + .bus = &usb_bus_type,
> + .find_bridge = NULL,
> + .find_device = usb_acpi_find_device,
> +};
I don't understand exactly how this is supposed to work. Does this
mean that the ACPI core will call usb_acpi_find_device() for every ACPI
device whose underlying real device is registered on the usb_bus_type?
If so, when does this call take place?
Or does it work some other way?
Bear in mind that USB devices aren't the only things registered with
usb_bus_type. We also register device structures representing USB
interfaces and endpoints. Hence the to_usb_device() call above might
not always do what you want.
Alan Stern
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