On Tue, Feb 21, 2012 at 1:44 PM, Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> wrote: >> (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. Excellent! > 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. It's quite common I think, many platforms have an intimate relation between GPIO and muxes/altfunctions. For example it is common that the hardware engineer doesn't helpfully enable on-die pull-ups on the I2C bus even though the I2C block is muxed in, you have to go in and set the pull-up bits separately from muxing the I2C in... Basically it's expected from a generic pad I/O cell being arrayed into a GPIO block to expose these things in the same set of registers. I made some presentation last week partly describing how some hardware engineers I know go about creating GPIO controllers from simpler I/O pad cells: http://www.df.lth.se/~triad/papers/pincontrol.pdf Yours, Linus Walleij -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
