[PATCH 1/2] Documentation/gpio.txt: Explain expected pinctrl interaction

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Tue, Feb 21, 2012 at 01:40:05PM +0100, Linus Walleij wrote:
> Of course it assumes the SA1100 being converted to use pin control,
> I looked at it a bit and it seems simple enough since the GAFR
> register is a single "GPIO or something else"-switch for the GPIOs.
> (It'd probably need the SA1100 to be a bit more strict in using
> gpiolib in place for the direct assignments though, else the
> abstractions get a bit pointless anyway.)

That's mostly happened through my recent set of 100 or so patches.
There's a few areas where that's not quite as easy as it should be,
but on the whole, it's mostly complete.

The other thing I forgot to mention, and I suspect it's particular to
SA11x0, is that the GPDR must be set correctly according to the special
function as well as GAFR.  So, if a special function involves driving
a pin, the pin must be set as an output in GPDR.  Conversely, if the
special function involves input only, the pin must be set as an input
in GPDR.

So, on SA11x0, gpio and pin configuration are intimately linked.