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

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Message-ID: <1420820083.28652.7.camel@mm-sol.com>
Date:	Fri, 09 Jan 2015 18:14:43 +0200
From:	"Ivan T. Ivanov" <iivanov@...sol.com>
To:	Lars-Peter Clausen <lars@...afoo.de>
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 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. 

Regards,
Ivan 
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