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SubjectRe: [PATCH v4 5/5] usb: gadget: udc-core: independent registration of gadgets and gadget drivers
On Thu, 12 Mar 2015, Ruslan Bilovol wrote:

> Change behavior during registration of gadgets and
> gadget drivers in udc-core. Instead of previous
> approach when for successful probe of usb gadget driver
> at least one usb gadget should be already registered
> use another one where gadget drivers and gadgets
> can be registered in udc-core independently.
>
> Independent registration of gadgets and gadget drivers
> is useful for built-in into kernel gadget and gadget
> driver case - because it's possible that gadget is
> really probed only on late_init stage (due to deferred
> probe) whereas gadget driver's probe is silently failed
> on module_init stage due to no any UDC added.
>
> Also it is useful for modules case - now there is no
> difference what module to insert first: gadget module
> or gadget driver one.


> @@ -366,9 +383,16 @@ found:
> list_del(&udc->list);
> mutex_unlock(&udc_lock);
>
> - if (udc->driver)
> + if (udc->driver) {
> + struct usb_gadget_driver *driver = udc->driver;
> +
> usb_gadget_remove_driver(udc);
>
> + mutex_lock(&udc_lock);
> + list_add(&driver->pending, &gadget_driver_pending_list);
> + mutex_unlock(&udc_lock);
> + }

I'm not sure this is a good idea. Gadget drivers probably don't expect
to be bound again after they are unbound.

Besides, when would this gadget driver get bound to a UDC? Not until
the next UDC is added -- even if there already are some unbound UDCs.


> @@ -468,6 +491,16 @@ int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
> break;
> }
>
> + if (ret) {
> + struct usb_gadget_driver *tmp;
> +
> + list_for_each_entry(tmp, &gadget_driver_pending_list, pending)
> + if (tmp == driver) {
> + list_del(&driver->pending);
> + ret = 0;
> + break;
> + }
> + }

You could avoid this loop and simply do list_del(&driver->pending), if
you made sure driver->pending was initialized.

Alan Stern



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