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

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Message-ID: <20130917104852.GN21013@sirena.org.uk>
Date:	Tue, 17 Sep 2013 11:48:52 +0100
From:	Mark Brown <broonie@...nel.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Sylwester Nawrocki <s.nawrocki@...sung.com>,
	Kevin Hilman <khilman@...aro.org>, 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>, Aaron Lu <aaron.lu@...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 Tue, Sep 17, 2013 at 03:25:25AM +0200, Rafael J. Wysocki wrote:
> On Tuesday, September 17, 2013 12:31:11 AM Mark Brown wrote:

> > It shouldn't even need to do that, it should just be able to rely on the
> > controller to power itself up when asked to do work.   This is how the
> > existing implementations are done - the controller power management is
> > totally transparent to the slave.

> If both the I2C client and I2C controller have corresponding objects in the
> ACPI namespace and the client's object is a child of the controller's object,
> then in order to power up the client we need to power up the controller even
> if no transactions are going to be carried out.  That's what the spec simply
> requires us to do in that case.

Like I said I think this should be handled by the power domains (or
otherwise in the ACPI specific code) - we shouldn't be needing to modify
individual drivers to work around thoughtlessness in the ACPI spec.

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