linux-kernel - Re: [PATCH v3 1/3] usb: udc: allow adding and removing the same gadget device

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Date:   Wed, 12 Apr 2017 10:33:34 +0300
From:   Felipe Balbi <balbi@...nel.org>
To:     Greg KH <greg@...ah.com>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Roger Quadros <rogerq@...com>, vivek.gautam@...eaurora.org,
        USB list <linux-usb@...r.kernel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] usb: udc: allow adding and removing the same gadget device


Hi,

Greg KH <greg@...ah.com> writes:
>> Here's what we have for most UDCs (net2280.c included):
>> 
>> 	struct my_udc {
>>         	struct gadget gadget;
>>                 [...]
>> 	};
>> 
>> 	probe()
>>         {
>>         	struct my_udc *u;
>> 
>> 		u = kzalloc(sizeof(*u), GFP_KERNEL);
>>                 [...]
>> 		return 0;
>> 	}
>> 
>> Now, if this kzalloc() would be replaced with devm_kzalloc() wouldn't
>> this result on a functionally equivalent execution to the patch I
>> proposed above?
>> 
>> Iff we change struct gadget to contain a struct device *dev instead of a
>> struct device dev, then sure, we will need to cope with proper
>> ->release() implementations.
>> 
>> As it is, it brings nothing to the table, IMO.
>
> You always have to have a release function for a kobject, no matter
> where it is, as it is being reference counted.  To not do so, is a huge
> indication of a problem in the design.

okay, this goes all the way back to when Dave B wrote the API, it has
always had empty ->release() functions (not all UDCs, though). I'll make
sure to review all of this for v4.13.

-- 
balbi

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