Re: New multi-use device

On Fri, 26 Oct 2007, Pete Zaitcev wrote:

> >     2) I wanted to be able to switch configurations via an IOCTL call so
> > I started to add the
> >        code for this into the device_ioctl routine and after browsing
> > the code for 
> >        "usb_set_configuration()" found out by reading the comments in
> > the code that this is 
> >        not really the best way to do it, but then what is the best way
> > to do this? []
> 
> I suspect Alan is the only one who knows the intent behind the
> current code.

Surely things aren't _that_ bad!  :-)

The basic idea behind the kernel's implementation is that configuration
changes are initiated by userspace.  If a program uses usbfs or libusb,
it can make a simple function call to change the device's config.  
Even a stupid shell script can change a config by writing to
/sys/bus/usb/devices/.../bConfigurationValue.

If a kernel driver wants to set a particular config then it should call 
usb_driver_set_configuration() from within its probe method and then 
return an error code such as -EIO.  This function lies in 
drivers/usb/core/messages.c and the kerneldoc explains how the function 
works.

Alan Stern


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