Messages in this thread | | | Date | Thu, 27 Jun 2013 12:18:15 +0200 | Subject | Re: [PATCH] pinctrl: elaborate a bit on arrangements in doc | From | Linus Walleij <> |
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On Wed, Jun 26, 2013 at 3:15 PM, Christian Ruppert <christian.ruppert@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
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