Re: [patch 2.6.24-rc3] usb peripheral controller driver oops avoidance

On Mon, 19 Nov 2007, David Brownell wrote:

> On Monday 19 November 2007, David Brownell wrote:
> > OK, I'll take the dummy_hcd bit out -- but add a comment to
> > highlight this unique behavior.
> 
> Currently expecting:
> 
> --- at91.orig/drivers/usb/gadget/dummy_hcd.c	2007-11-19 13:58:57.000000000 -0800
> +++ at91/drivers/usb/gadget/dummy_hcd.c	2007-11-19 13:58:55.000000000 -0800
> @@ -779,6 +779,13 @@ usb_gadget_register_driver (struct usb_g
>  	if ((retval = driver->bind (&dum->gadget)) != 0)
>  		goto err_bind_gadget;
>  
> +	/* NOTE:  most peripheral controller drivers won't bother
> +	 * registering the gadget drivers, since doing that requires
> +	 * that the driver be associated with a bus.  There's really
> +	 * no existing bus that's appropriate for a gadget driver,
> +	 * and little point in defining a "bus" that must never have
> +	 * more than one device.
> +	 */
>  	driver->driver.bus = dum->gadget.dev.parent->bus;
>  	if ((retval = driver_register (&driver->driver)) != 0)
>  		goto err_register;

Now that I look back on it, it's not so clear that the scheme used by
dummy_hcd is really correct.  It registers a driver structure on the
platform bus but embeds it inside a usb_gadget_driver instead of a
platform_driver.  This sounds like a bug waiting to happen.

Maybe it would be better to change dummy_hcd to make it work like the
other device controller drivers.  There seems to be no advantage to
registering the gadget driver in sysfs (and some disadvantage in that
the Gadget API doesn't match up well with normal bus-oriented probe and
remove methods).

Greg, do you agree with that last sentence?

Alan Stern


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