linux-kernel - Re: [PATCH v4 5/5] usb: gadget: udc-core: independent registration of gadgets and gadget drivers

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Date:	Fri, 13 Mar 2015 10:39:58 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ruslan Bilovol <ruslan.bilovol@...il.com>
cc:	balbi@...com, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <k.opasiak@...sung.com>,
	<peter.chen@...escale.com>, <gregkh@...uxfoundation.org>,
	<andrzej.p@...sung.com>
Subject: Re: [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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