linux-kernel - Re: [PATCH v7 4/4] usb: gadget: udc-core: independent registration of gadgets and gadget drivers

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Date:	Mon, 23 Nov 2015 10:32:53 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Marek Szyprowski <m.szyprowski@...sung.com>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	Ruslan Bilovol <ruslan.bilovol@...il.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v7 4/4] usb: gadget: udc-core: independent registration
 of gadgets and gadget drivers

On Mon, 23 Nov 2015, Marek Szyprowski wrote:

> From: Ruslan Bilovol <ruslan.bilovol@...il.com>
> 
> 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.
> 
> Tested-by: Maxime Ripard <maxime.ripard@...e-electrons.com>
> Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
> [simplified code as requested by Alan Stern and Felipe Balbi,
>  fixed checkpatch issues]
> Signed-off-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Tested-by: Peter Chen <peter.chen@...escale.com>

I missed this the last time through...

> @@ -403,6 +408,18 @@ int usb_add_gadget_udc_release(struct device *parent, struct usb_gadget *gadget,
>  	usb_gadget_set_state(gadget, USB_STATE_NOTATTACHED);
>  	udc->vbus = true;
>  
> +	/* pick up one of pending gadget drivers */
> +	list_for_each_entry(driver, &gadget_driver_pending_list, pending) {
> +		if (!driver->udc_name || strcmp(driver->udc_name,
> +						dev_name(&udc->dev)) == 0) {
> +			ret = udc_bind_to_driver(udc, driver);
> +			if (ret)
> +				goto err4;
> +			list_del(&driver->pending);

This has to be list_del_init().  And somewhere in
usb_gadget_probe_driver() you need to do
INIT_LIST_HEAD(&driver->pending).

> @@ -577,6 +596,10 @@ int usb_gadget_unregister_driver(struct usb_gadget_driver *driver)
>  			break;
>  		}
>  
> +	if (ret) {
> +		list_del(&driver->pending);

Otherwise this will cause a crash or corrupt some random area of 
memory.

Alan Stern

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