Re: [PATCH] i2c: Add generic support passing secondary devices addresses

[Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>]

Hi Lars and Jean,

Are you taking this patch further to take care about ACPI related stuff
submitted by Mika?

Thanks,
Srinivas
On Fri, 2014-10-03 at 12:46 +0200, Wolfram Sang wrote: 
> > > Ok, looks like there are two main differences in the two implementations.
> > > 
> > > 1) The ACPI one uses a integer index and the DT one uses a string index to
> > > lookup the device.
> > > 
> > > The problem with the index lookup is that the order is binding specific. So
> > > it might be different between e.g. the devicetree binding and the ACPI
> > > binding. This makes it quite hard to use the API in a generic way and you'd
> > > end up with hacks like:
> > > 
> > > if (client->dev.of_node)
> > > 	index = 3;
> > > else if (ACPI_COMPANION(client->dev))
> > > 	index = 1;
> > > else
> > > 	index = 5;
> > > 
> > 
> > Indeed.
> > 
> > > So we might need a extra translation table which maps a name to a ACPI index
> > > and then we could use the name as the generic index in the driver.
> > 
> > Good thing is that ACPI 5.1 _DSD finally allows us to use similar naming
> > as the DT has been doing. Problem is that we need to support both the
> > new way *and* the older index lookup somehow :-/
> > 
> > > 2) The ACPI implementation returns the i2c_board_info and the adapter, while
> > > the DT implementation returns the instantiated I2C client device.
> > > 
> > > It might make sense to have both. I image that most drivers are just
> > > interested in creating a new client device and will simply pass the board
> > > info and adapter they got to i2c_new_device(). In this case it makes sense
> > > to have a helper function which already does this internally to avoid
> > > boilerplate code duplication.
> > 
> > I agree. How about making that helper a wrapper around the function that
> > returns both i2c_board_info and an adapter?
> > 
> > > There will probably some special cases though in which case the driver wants
> > > to get the adapter and the board info and then manually call
> > > i2c_new_device() after having done some additional steps.
> > 
> > Yes, if the alternative address happens to be on another bus. That
> > should at least be possible with this API.
> 
> Thanks for the discussion so far! I'll wait and see if some patches come
> out of it and mark this one as deferred for now.
>