linux-kernel - Re: [PATCH v2 1/9] i2c: prepare runtime PM support for I2C client devices

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Date:	Fri, 13 Sep 2013 11:02:02 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Aaron Lu <aaron.lu@...el.com>
Cc:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	linux-i2c@...r.kernel.org, Wolfram Sang <wsa@...-dreams.de>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	Lv Zheng <lv.zheng@...el.com>,
	linux-arm-kernel@...ts.infradead.org,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Mauro Carvalho Chehab <m.chehab@...sung.com>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Kyungmin Park <kyungmin.park@...sung.com>
Subject: Re: [PATCH v2 1/9] i2c: prepare runtime PM support for I2C client
 devices

On Fri, Sep 13, 2013 at 09:14:20AM +0800, Aaron Lu wrote:
> On 09/13/2013 06:06 AM, Sylwester Nawrocki wrote:

> > So there is currently no way to avoid this behaviour, i.e. to have the 
> > adapter
> > not activated before any of its client devices is probed, but only later on,
> > after explicit call to pm_runtime_get*(&client->dev) in the client driver ?

> The above pm_runtime_get_sync is used to make sure when the client I2C
> device is going to be probed, its host adapter device is turned on(or we
> will fail the probe). It doesn't affect the adapter's status before the
> probe of I2C client device.

The expecation is that if the adaptor needs to do anything to transfer
it'll do that when asked to transfer - that way it can sit in a low
power state when the bus is idle.

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