[PATCH RESEND] i2c: Add support for device-tree based chip initialization

[Guenter Roeck]

On Mon, Nov 26, 2012 at 04:26:39PM -0800, David Daney wrote:
> On 11/26/2012 12:13 PM, Grant Likely wrote:
> >On Sun, 25 Nov 2012 20:53:56 -0800, Guenter Roeck <linux at roeck-us.net> wrote:
> >>Some I2C devices are not or not correctly initialized by the firmware.
> >>Configuration would be possible via platform data, but that would require
> >>per-driver platform data and a lot of code, and changing it would not be
> >>possible without re-compiling the kernel. It is more elegant to do it
> >>generically via devicetree properties.
> >>
> >>Add a generic I2C devicetree property named "reg-init". This property provides
> >>a sequence of device initialization commands to be executed prior to calling
> >>the probe function for a given device.
> >>
> >>Signed-off-by: Guenter Roeck <linux at roeck-us.net>
> >
> >This is a very similar problem to the power sequences series that was
> >recently posted to this list. I would like that feature and this
> >mechanism use the same approach.
> 
> 
> I haven't fully studied the power sequencing thing, but just to play
> Devil's Advocate, there is precedence for the "reg-init" style in
> some of the Ethernet PHY drivers.
> 
That is where I took it from.

> Perhaps the "reg-init" should be used as one of the steps in the
> sequence, and if there was only a single step it would be
> functionally equivalent to the "reg-init" proposal.
> 
My thought is along the same line. I'll have to study the power sequencing
proposal a bit more to see if that would work.

Guenter