Pinmuxing (Loadable) Kernel Module?

[TJF]

In my practical work pinmuxing is a daily issue. Available solutions are anoying:

• The device tree configuration at boot time is too unflexible.
• The universal_io solutions are much better, but unusable for my purposes since they use human readable names.
• So I made a similar solution using numbers, but it's a pitty to bloat the kernel memory by so much device tree entries. Most of them unused all the time. And often I'd like to use a further mode, not yet pre-defined.

What I miss is a simple and flexible solution. A kernel module that provides a single entry in sysfs:

• Write access (root privileges) configures a pin (if not reserved), ie. like
  
• value 0x010c002e sets CM register at offset 0x010c to mode 0x2e, or alternatively
• value 0x6c3f sets ball number 0x6c to mode 0x3f, or anything similar.
• Optional: Read access returns a list of all current ball configurations in the same format (with a mark free / reserved).

Does anybody

• knows about,
• uses,
• develops (or is willing to develop)

such a kernel module?

[TJF]

Posts copied from https://groups.google.com/d/msg/beagleboard/Ie-gxRfFJTc/RyGQf1ShAgAJ:

You mean like this?

https://www.kernel.org/doc/Documentation/gpio/sysfs.txt

Regards,

John

...

That should read add mode feature

Yes and no ...

The user space aspect is what I mean. But I'm speaking about pin muxing. That is

• all that GPIO stuff in your document, as well as
• the ball mode feature (GPIO, CAP, PWM, ...) and
• pullup /pulldown restistor settings.

Instead of several folders and files in sysfs and human readable parameters, I'd like to see

• a single entry that
• gets opened once and can
• controll all free pins by a single write access,
• receiving a single parameter that is a combination of ball#/value (or register offset/value - like in the device tree source).

The pins to operate on could get defined in the device tree. But it'd be better when the driver could auto-determine them (the not reserved one).

In short, I'm searching for a solution to set the parameters of a device tree entry like

B08_28: 08_28 {pinctrl-single,pins = <0x020 0x28>;};

at run time via sysfs.

Regards,
Thomas

[John Syne]

Well, that is what I meant by mode, which is pinmux Mode1 through Mode7, plus the pullup, pulldown, direction, etc. Rather than starting from scratch, I think it would be simple to add this to gpiolib. Also, gpiolib has uses debugfs to display info about the gpio pins. Look at /sys/kernel/debug/gpio. Not sure how you would implement this in a generic way so that it would apply to other architectures. Without this, I don’t believe it will be accepted by mainline. 

Regards,

John

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[TJF]

Hi John, please excuse my late reply. I haven't been in the office for a while.

I agree, it wouldn't be easy the implement this in a generic way to the gpiolib driver. And even if possible, we'll end up with a pinmux feature in a driver named gpiolib. Another stumbling stone in the big "find the right driver" game. Sure, that's not the way to go.

But what about adapting the driver pinctrl-single? This driver has all features we need. We just have to implement entries in sysfs to additionally control the pins after boot time. I see no reason why that shouldn't be possible in a generic way for all architectures.

Your statement is much appriciated.

BR