On 06/25/2013 08:19 AM, Linus Walleij wrote: > From: Linus Walleij <linus.wall...@linaro.org> > > This elaborates a bit on the pinctrl vs GPIO arangements > in the hardware. > > Inspired by some drawings in a mail from Christian > Ruppert.
> diff --git a/Documentation/pinctrl.txt b/Documentation/pinctrl.txt > +The GPIO portions of a pin and its relation to a certain pin controller > +logic can be constructed in several ways. Here are three examples: > + > +(A) > + > + +- SPI > + Physical pins --- GPIO --- pinctrl -+- I2C > + +- mmc > + > +(B) > + +- GPIO > + Physical pins -+ +- SPI > + +- pinctrl -+- I2C > + +- mmc > + > +(C) > + +- SPI > + Physical pins --- pinctrl -+- I2C > + +- mmc > + +- GPIO I'm not really sure quite what these diagrams are attempting to convey within the context of this document. > +In (A) the GPIO-like functionality of the pin is *always* available. Well, that can't really be true. It may be possible that you can always read the physical pin's value via a GPIO input register. However, you obviously can't always write to a GPIO output register to set the pin's value. If you could, the pin would simply be a GPIO, and never serve any other function. If you're saying that it's always possible to put the pin into a mode where you can use the GPIO output register to driver the pin value, well then that's just regular pin-muxing, so I'm not sure why it's worth mentioning. In (a) there are really two levels of pinmux configuration, one in the GPIO HW block (GPIO-vs-whatever-pinctrl-selects). In (b) there is another level of pinmux configuration; some block has to exist between the physical pins and both GPIO/pinctrl HW modules; it simply isn't drawn in the diagram Diagram (c) appears complete. In all cases though, this is just attempting to enumerate different HW designs for pin-muxing I think. Isn't it better to just let each SoC's datasheet specify exactly how things are hooked up? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
