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

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Message-ID: <Pine.LNX.4.44L0.1501291052380.1837-100000@iolanthe.rowland.org>
Date:	Thu, 29 Jan 2015 10:56:29 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Ruslan Bilovol <ruslan.bilovol@...il.com>
cc:	linux-usb@...r.kernel.org, <linux-kernel@...r.kernel.org>,
	<balbi@...com>, <gregkh@...uxfoundation.org>,
	<andrzej.p@...sung.com>
Subject: Re: [PATCH 1/2] usb: gadget: udc-core: independent registration of
 gadgets and gadget drivers

On Thu, 29 Jan 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.

It's possible to do all this much more simply.  In fact, I posted a 
patch some time ago to do exactly this (but I can't find a copy of it 
anywhere).

> Signed-off-by: Ruslan Bilovol <ruslan.bilovol@...il.com>
> ---
>  drivers/usb/gadget/udc/udc-core.c | 113 +++++++++++++++++++++++++++++++++++---
>  1 file changed, 105 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/usb/gadget/udc/udc-core.c b/drivers/usb/gadget/udc/udc-core.c
> index e31d574..4c9412b 100644
> --- a/drivers/usb/gadget/udc/udc-core.c
> +++ b/drivers/usb/gadget/udc/udc-core.c
> @@ -43,13 +43,23 @@ struct usb_udc {
>  	struct usb_gadget_driver	*driver;
>  	struct usb_gadget		*gadget;
>  	struct device			dev;
> +	bool				bind_by_name;
> +	struct list_head		list;
> +};
> +
> +struct pending_gadget_driver {
> +	struct usb_gadget_driver	*driver;
> +	char				*udc_name;
>  	struct list_head		list;
>  };

You don't need all this stuff.  What's the point of keeping track of
names?  If there are any unbound gadget drivers pending, a newly
registered UDC should bind to the first one available.

Just add a "pending" list_head into the usb_gadget_driver structure and 
forget about all the rest.  (Or try to find my patch in the mailing 
list archives somehow see if you think it needs to be changed.)

Alan Stern

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