On Mon, 12 Mar 2012, Matthew Garrett wrote:
> > > +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?
>
> Kind of? platform_notify gets called whenever a device is registered,
> and on ACPi systems that'll be acpi_platform_notify. It'll take the
> registered device and, if there are glue functions for that bus type,
> pass it to the callback functions. The idea is that we have two
> disparate device trees, the Linux one and the ACPI one. This just gives
> us an opportunity to glue some of the devices together.
Ah, okay.
> > 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.
>
> Ugh. Is there any clean way to distinguish from the device structure? If
> not, the easiest would seem to be to just add another bus type
> structure, even if the members are identical.
Easy; just call is_usb_device() (defined in core/usb.h).
Alan Stern
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