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

On Sun, Sep 15, 2013 at 09:41:39AM +0300, Mika Westerberg wrote:

There's also a less intrusive way of fixing the problem we see with ACPI
enabled I2C devices:

	1. In I2C core i2c_device_probe() we power on the I2C controller
	and attach the client device to the ACPI power domain. Just like in
	this patch but we don't touch the I2C client device runtime PM.

	-> This should allow the existing drivers to keep using whatever
	runtime PM strategy they have chosen.

There should be no explicit need to power on the I2C controller if it's
implemented the same way the existing ones are - just have it power
itself on when it is doing a transfer.

	2. For ACPI enumerated I2C client devices drivers we need to
	implement the runtime PM in order to save power (otherwise the
	devices will be left powered on).

and do the same for SPI devices as well.

Then only thing that changes for non-ACPI devices is that the controller
will be powered on during the client device probe (well, and during
remove).

Thoughts?

This is definitely less intrusive than the current proposal, there's one
ACPI I2C device binding queued for -next after the merge window (rt5640)
which will need an update.
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