On Wed, Jun 26, 2013 at 3:15 PM, Christian Ruppert <christian.rupp...@abilis.com> wrote:
> In my experience, in hardware engineering terminology, GPIO/General > Purpose I/O just means a physical pad macro cell which can be > dynamically configured in different modes, e.g. as an input or as an > output, as an open drain driver etc. This configuration is done through > hardware signals and controlled by digital logic. This logic might > either be a GPIO controller or some other hardware block, e.g. an I2C > controller block. This is what this patch is trying to hash out. Have you seen this presentation I did a while back? http://www.df.lth.se/~triad/papers/pincontrol.pdf > Hardware GPIOs have nothing to do with the concept of GPIOs from the > Linux kernel point of view That is unfortunately a bit of HW engineering terminology problem. It took some months before we came up with the three non-overlapping (well) sets of "GPIO", "pin configuration" and "pin multiplexing" to sort these things into three different buckets. And this entire section in Documentation/pinctrl.txt is trying to explain this to the kernel developer. > In some cases, both modes are combined, e.g. one can imagine an SPI > interface where the output levels are driven from an SPI controller > hardware block and other parameters such as the drive strength or > integrated pull-up/pull-down resistors are controlled through some > independent mechanism. This is the case on the Nomadik and I think many other pin controllers. But on the U300, the output line is controlled by two things at the time! > The parameters controlled through that > independent mechanism are sometimes referred to as the GPIO mode of the > pin. Yes... Yours, Linus Walleij -- 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/
