On Wed, 2 Dec 2009, Alan Stern wrote:
> On Mon, 30 Nov 2009, Sarah Sharp wrote:
>
> > Refactor out the code to find alternate interface settings into
> > usb_find_alt_setting(). Print a debugging message and return null if the
> > alt setting is not found.
> > /**
> > + * usb_find_alt_setting() - Given a configuration, find the alternate setting
> > + * for the given interface.
> > + * @config - the configuration to search (not necessarily the current config).
> > + * @iface_num - interface number to search in
> > + * @alt_num - alternate interface setting number to search for.
> > + *
> > + * Search the configuration's interface cache for the given alt setting.
> > + */
> > +struct usb_host_interface *usb_find_alt_setting(
> > + struct usb_host_config *config,
> > + unsigned int iface_num,
> > + unsigned int alt_num)
> > +{
> > + struct usb_interface_cache *intf_cache;
> > + int i;
> > +
> > + intf_cache = config->intf_cache[iface_num];
>
> This is wrong. The entries in the interface_cache array are not stored
> in order (more accurately, they are stored in the order of the
> descriptors sent by the device, whatever that happens to be). You have
> to search to find the right one.
And I forgot to mention, the second search can be replaced with a call
to usb_altnum_to_altsetting().
Alan Stern
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