Passing I2C platform_data from device tree to i2c driver

[Nate Case <ncase@xes-inc.com>]

Is there a plan for providing a way to set pdata for an I2C chip in a
way that could be shared across all OF platforms?

For example, the pca953x I2C GPIO driver requires that pdata != NULL so
it can get the gpio_base field.  It can also take in a default 'invert'
value to initialize a chip register with.  Currently, there's no obvious
way to get this to work on PowerPC without hardcoding things in the
arch/powerpc/platforms/*.c file.

On ARM platforms, they currently handle this by declaring
I2C_BOARD_INFO() in their board-specific files.  For OF platforms, I
think the obvious choice would be to specify platform data in the device
tree.  We already register I2C devices automatically as found in the
device tree (see drivers/of/of_i2c.c), but this registration method does
not provide any way to set platform_data.

Of course, I could put some code in my board specific file to parse the
device tree properties and set pdata accordingly, but this hardly seems
ideal.  After all, the device tree bindings -> pdata translation itself
does not have to be board-specific.

Basically, I think we need to have some common code somewhere that does
the task of populating platform_data for a specific I2C chip based on a
device tree node -- similarly to how we register the I2C devices
already.  Is anyone working on this?  Did anyone have anything else in
mind?

-- 
Nate Case <ncase@xes-inc.com>