Re: [RFC] Rework of i2c-mpc.c - Freescale i2c driver

["Grant Likely" <grant.likely@secretlab.ca>]

On 11/6/07, Jean Delvare <khali@linux-fr.org> wrote:
> Hi Scott,
>
> On Tue, 06 Nov 2007 11:36:23 -0600, Scott Wood wrote:
> > Jean Delvare wrote:
> > >>>> We might as well just use i2c_new_device() instead of messing around
> > >>>> with bus numbers.  Note that this is technically no longer platform
> > >>>> code, so it's harder to justify claiming the static numberspace.
> > >>> I was allowing control of the bus number with "cell-index" and
> > >>> i2c_add_numbered_adapter().
> > >>> Should I get rid of this and switch to i2c_add_adapter()?
> > >> Yes.
> > >
> > > No! If you don't call i2c_add_numbered_adapter() then new-style i2c
> > > clients will never work on your i2c adapter.
> >
> > I thought that was what i2c_new_device() was for?
>
> Sorry, I've not been completely clear. Yes, you can use
> i2c_new_device() on an adapter that has been added with
> i2c_add_adapter(). However, this requires that you have a reference to
> that i2c_adapter, which is usually not the case with system-wide I2C
> buses. Embedded platforms would rather use i2c_add_numbered_adapter(),
> give a list of chips to i2c_register_board_info() and let i2c-core
> instantiate them. i2c_new_device was primarily meant for multimedia
> adapters.

*Some* embedded platforms would rather use i2c_add_numbered_adapter().  :-)

On powerpc, and other platforms which have a device tree, we don't
need to define a table of devices in the platform code because we've
already got a rich structure for describing such things.  The i2c
busses and i2c devices are grouped together in the device tree, so
when the i2c bus is probed, it should call out to common i2c device
tree parsing code to instantiate all the devices described in the
tree.

It would be awkward to describe the i2c bus in the device tree but
still have to use a static structure to describe the devices on that
bus.

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
grant.likely@secretlab.ca
(403) 399-0195