Re: [Ksummit-discuss] [TECH TOPIC] Driver model/resources, ACPI, DT, etc (sigh)

["Rafael J. Wysocki" <rjw@rjwysocki.net>]

On Saturday, May 17, 2014 02:24:23 PM Mark Brown wrote:
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> On Thu, May 15, 2014 at 02:05:43PM +0200, Rafael J. Wysocki wrote:
> > On Wednesday, May 14, 2014 02:04:01 PM Mark Brown wrote:
> 
> > > Of course, and for all of these things other than GPIOs we already
> > > handle the lookups without any DT code at all in the drivers (and GPIOs
> > > are moving away from needing explicit code too).  Things like that just
> > > aren't an issue and I'd say that if we are adding new fw_ interfaces for
> > > resource lookup like you describe we're doing things wrong, we already
> > > have the idiom of looking up by device and some key which works well.
> 
> > The "key" think doesn't really work in ACPI if it is a string, however.
> 
> > That's a real problem, because, for example, ACPI says "I have these GPIO
> > connections between your device and controller X" and it gives you pin
> > numbers.  Now the driver (or someone else) needs to figure out which pin
> > is used for what.
> 
> > If there's only one pin per device, all is fine, but if there are more of
> > them things get very ugly quite quickly.
> 
> > So in "native" ACPI something like gpiod_get() cannot really be implemented
> > to use con_id and if you look at acpi_find_gpio() (the one in gpiolib.c),
> > you'll see that it actually only uses the index for this very reason.
> 
> Surely all we need to do for these cases is provide a way for drivers to
> supply the name to number mappings for usage with ACPI (probably with
> per device and per board overrides possible due to all the failures
> usually associated with numbers)?

Yes, we can do that for things like gpiod_get() that already abstract the
firmware interface away from device drivers.

> That's much less invasive than making new APIs.

But for drivers that call of_get_something() directly I don't see any other
sensible way forward.  Otherwise each of them will need to do something like

if (dev->of_node)
	use of_get_X()
else if (ACPI_COMPANION(dev))
	use acpi_get_X()
else
	use black magic

possibly in several places.

Rafael