linux-kernel - Re: [PATCH] iio: Simplify IIO provider access locking mechanism

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Message-ID: <54AFFEF9.5080408@metafoo.de>
Date:	Fri, 09 Jan 2015 17:16:57 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	"Ivan T. Ivanov" <iivanov@...sol.com>
CC:	Jonathan Cameron <jic23@...nel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Peter Meerwald <pmeerw@...erw.net>, linux-iio@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: Simplify IIO provider access locking mechanism

On 01/09/2015 05:14 PM, Ivan T. Ivanov wrote:
>
> On Fri, 2015-01-09 at 16:54 +0100, Lars-Peter Clausen wrote:
>> On 01/09/2015 04:50 PM, Ivan T. Ivanov wrote:
>>> On Fri, 2015-01-09 at 16:41 +0100, Lars-Peter Clausen wrote:
>>>> On 01/09/2015 04:38 PM, Ivan T. Ivanov wrote:
>>>>> Instead of checking whether provider module is still
>>>>> loaded on every access to device just lock module to
>>>>> memory when client get reference to provider device.
>>>>>
>>>>
>>>> This has nothing to do with the module, it's about the device. In the Linux
>>>> device driver model as device can be unbound at any time and the IIO
>>>> framework needs to handle this.
>>>>
>>>
>>> Hm. Probably i am missing something here, but is this
>>> still true if we have reference to device structure?
>>
>> Yes, that only prevents the memory of device from being freed. But the
>> device can still be unbound from the driver.
>>
>> Think of e.g. a USB device that is pulled from the USB connector. Nothing
>> you can do in software about having the device disappear.
>>
>
> Agree, but I think that the patch is still valid. Module
> have to be pinned in memory as long as there are device
> driver users.

No, the idea of the Linux driver model is that you can remove the module of 
a driver at any time, which will unbind the device from the driver. Once you 
reinsert the module the device will be re-bound to the driver.

- Lars

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