[i2c] [PATCH] Convert i2c-mpc from a platform driver to an of_platform one

[Grant Likely]

On Sat, Jun 28, 2008 at 10:05:28PM -0400, Jon Smirl wrote:
> On 6/25/08, Jean Delvare <khali at linux-fr.org> wrote:
> >  >
> >  >       i2c->adap = mpc_ops;
> >  > -     i2c->adap.nr = pdev->id;
> >  >       i2c_set_adapdata(&i2c->adap, i2c);
> >  > -     i2c->adap.dev.parent = &pdev->dev;
> >  > -     if ((result = i2c_add_numbered_adapter(&i2c->adap)) < 0) {
> >  > +     i2c->adap.dev.parent = &op->dev;
> >  > +
> >  > +     result = i2c_add_adapter(&i2c->adap);
> >
> >
> > The driver was previously using i2c_add_numbered_adapter(), giving MPC
> >  platform the possibility to use new-style i2c drivers:
> >  http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=1469fa263870acd890a4b9f6ef557acc5d673b44
> >  You're breaking this, I doubt it's on purpose?
> 
> Grant, what do you want here? You're the one who converted it to
> i2c_add_numbered_adapter. But in other posts you've said that the
> device tree should have nothing to do with bus numbering.

Yes, I did make that change, but that was when it was a platform bus
driver.  Converting it to an of_platform bus driver entirely changes the
situation and it should go back to using i2c_add_adapter() with a parse
of the device tree for child nodes.

> Once this driver is converted to an OF one it shouldn't need bus ids
> since all of the i2c devices will be children of the bus node. We can
> just let the i2c subsystem assign a bus number.

Exactly.

> Timur has some issues with the i2c bus number in his ALSA driver. The
> problem is locating the i2c device when the i2s driver loads. Parsing
> the device tree to extract an i2c bus and device number is not a good
> solution.

The trick here is to store the pointer to the device node inside the
i2c device.  I do this with SPI devices like this:

	/* Store a pointer to the node in the device structure */
	of_node_get(nc);
	spi->dev.archdata.of_node = nc;

Then, when you've got a device_node pointer, you can parse through the
set of registered SPI devices and match against the one that has the
same device node pointer.

> codec-handle should give you the i2c device node. But then we can't
> use of_find_device_by_node because the i2c device is not an of_device,
> it's a cross platform i2c_device. Should of_find_device_by_node()
> return a 'struct device' instead of a 'struct of_device' and leave it
> as a user exercise to cast up? It is used nine times in the kernel,
> mostly sparc.

No, this doesn't work because I2C and SPI devices are not of_platform
devices.  They aren't even platform devices.  of_find_device_by_node()
only works for the of_platform bus.

Using archdata.of_node is part of the device structure and works for
every bus type (platform, of_platform, SPI, I2C, PCI, etc.)

g.