linux-kernel - Re: [PATCH 0/2] i2c-dev: Don't let userspace block adapter

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Message-ID: <577D1895.3060202@metafoo.de>
Date:	Wed, 6 Jul 2016 16:41:25 +0200
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Viresh Kumar <viresh.kumar@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	Jean Delvare <jdelvare@...e.com>
Cc:	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org,
	gregkh@...uxfoundation.org, Johan Hovold <johan@...nel.org>,
	Alex Elder <elder@...aro.org>
Subject: Re: [PATCH 0/2] i2c-dev: Don't let userspace block adapter

On 07/06/2016 04:57 AM, Viresh Kumar wrote:
> Hi Wolfram/Jean,
> 
> I am part of the kernel team for Google's projectara [1], where we are
> building a module smart phone.
> 
> This series tries to fix one of the problems we hit on our system as we
> are required to hotplug pretty much every thing on the phone and so this
> fixes hotplug issues with i2c-dev.
> 
> As described in the second patch, the current implementation of i2c-dev
> file operations doesn't let the modules (hardware attached to the phone)
> eject from the phone as the cleanup path for the module hasn't finished
> yet (i2c adapter not removed).
> 
> We can't let the userspace block the kernel devices forever in such
> cases.
> 
> I was able to test them on the ARA phone with kernel 3.10 only and not
> mainline.

This sounds like you want hot-unplug. This is currently not support by the
I2C framework for adapters. A better approach compared to this series might
be to implement full hot-unplug support for I2C adapters. This will probably
also be useful for additional usecases.