Re: [fedora-arm] Accessing GPIOs from userspace using recent kernels

On 2014-04-29 10:36, Peter TB Brett wrote:
> Hi all,
>
> We have several pieces of software that make use of the
> /sys/class/gpio userspace interface to the GPIO subsystem.
>
> One important prerequisite to being able to use the userspace GPIO
> interface is to be able to put the corresponding package pins into
> GPIO mode, by modifying the chip's mux settings.
>
> With Fedora 19 on the Pandaboard, we were able to achieve this by
> poking around in /sys/kernel/debug/omap_mux. However, when running
> Fedora 20, this directory is empty. My assumption is that this
> functionality has been subsumed by the pinctrl subsystem in recent
> kernels. Unfortunately, there doesn't seem to be any documented
> userspace API.
>
> I'd greatly appreciate it if someone could give me some pointers about
> how to deal with this issue!

I'm still looking for a solution to this problem!

Is there any way that I can simply amend the device tree in order to
change a couple of mux settings?

I've figured out that I would need a stanza that looks something like:

&omap4_pmx_core
{
foo_pins: pinmux_foo_pins {
pinctrl-single,pins = <
0x5e (PIN_INPUT | MUX_MODE3) /* gpmc_ad15.gpio_39 */ /* IRQ */
0x12e (PIN_INPUT | MUX_MODE3) /* i2c4_scl.gpio_132 */ /* RST */
};
};

But I can't work out what else I need to modify in order for these mux
settings to take effect.

Thanks for any pointers!

Peter

--
Dr Peter Brett <peter@peter-b.co.uk>
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