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

On Mon, Nov 26, 2012 at 04:26:39PM -0800, David Daney wrote:

On 11/26/2012 12:13 PM, Grant Likely wrote:

quoted

On Sun, 25 Nov 2012 20:53:56 -0800, Guenter Roeck [off-list ref] wrote:

quoted

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 <redacted>

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