linux-kernel - Re: [PATCH v2 1/2] usb: gadget: udc-core: independent registration of gadgets and gadget drivers

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Date:	Sun, 15 Feb 2015 18:23:02 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ruslan Bilovol <ruslan.bilovol@...il.com>
cc:	balbi@...com, <k.opasiak@...sung.com>, <peter.chen@...escale.com>,
	<linux-kernel@...r.kernel.org>, <gregkh@...uxfoundation.org>,
	<andrzej.p@...sung.com>
Subject: Re: [PATCH v2 1/2] usb: gadget: udc-core: independent registration
 of gadgets and gadget drivers

On Mon, 16 Feb 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.
> 
> Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
> ---
>  drivers/usb/gadget/udc/udc-core.c | 77 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 74 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
> index 5a81cb0..71b6942 100644
> --- a/drivers/usb/gadget/udc/udc-core.c
> +++ b/drivers/usb/gadget/udc/udc-core.c
> @@ -46,10 +46,18 @@ struct usb_udc {
>  	struct list_head		list;
>  };
>  
> +struct pending_gadget_driver {
> +	struct usb_gadget_driver	*driver;
> +	char				*udc_name;
> +	struct list_head		list;
> +};

Don't make this a separate structure.  It should be embedded in the 
usb_gadget_driver structure.  This will make a lot of the changes below 
much simpler.

> @@ -288,6 +297,24 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
>  
>  	usb_gadget_set_state(gadget, USB_STATE_NOTATTACHED);
>  
> +	if (!list_empty(&gadget_driver_pending_list)) {
> +		pending = list_first_entry(&gadget_driver_pending_list,
> +					struct pending_gadget_driver, list);
> +
> +		if (pending->udc_name) {
> +			if (!strcmp(pending->udc_name, dev_name(&udc->dev))) {
> +				udc_bind_to_driver(udc, pending->driver);
> +				list_del(&pending->list);
> +				kfree(pending->udc_name);
> +				kfree(pending);
> +			}
> +		} else {
> +			udc_bind_to_driver(udc, pending->driver);
> +			list_del(&pending->list);
> +			kfree(pending);
> +		}

This code can be simplified too:

		if (!pending->udc_name || strcmp(pending->udc_name, 
				dev_name(&udc->dev) == 0) {
			...
> +	}
> +
>  	mutex_unlock(&udc_lock);
>  
>  	return 0;

Don't you want to add a driver back to the pending list 
usb_del_gadget_udc() after the call to usb_gadget_remove_driver?

> @@ -423,7 +450,27 @@ int usb_udc_attach_driver(const char *name, struct usb_gadget_driver *driver)
>  			break;
>  	}
>  	if (ret) {
> -		ret = -ENODEV;
> +		struct pending_gadget_driver *pending;
> +
> +		pending = kzalloc(sizeof(*pending), GFP_KERNEL);
> +		if (!pending) {
> +			ret = -ENOMEM;
> +			goto out;
> +		}
> +		pending->driver = driver;
> +		pending->udc_name = kstrdup(name, GFP_KERNEL);
> +		if (!pending->udc_name) {
> +			kfree(pending);
> +			ret = -ENOMEM;
> +			goto out;
> +		}

Why do you need to copy the name?  Just use the original.

Alan Stern

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