[gonzo@freebsd.org: [RFC] GPIO framework]

Marc Balmer marc at msys.ch
Fri Nov 27 21:31:39 UTC 2009

Oleksandr Tymoshenko schrieb:
> Forwarding RFC to embedded@ because there was typo in Cc address in 
> the  original message :(
> ----- Forwarded message from Oleksandr Tymoshenko <gonzo at freebsd.org> -----
> Date: Thu, 26 Nov 2009 06:57:36 +0200
> From: Oleksandr Tymoshenko <gonzo at freebsd.org>
> To: arch at freebsd.org
> Cc: embedded at frebsd.org
> Subject: [RFC] GPIO framework
> User-Agent: Mutt/1.5.20 (2009-06-14)
> Recently I've been working on GPIO framework that, I believe, 
> is much needed for embedded applications of FreeBSD. Now framework
> is  mature enough to show it to the world, so this is my request 
> for review.
> Patch: http://people.freebsd.org/~gonzo/mips/gpio.diff
> sys/gpio.h is based on the same file from NetBSD but all the other 
> files have been written from the scratch.

why that?

> Description:
> GPIO stands for General Purpose Input/Output. This interface may be
> thought of as a set of pins which could serve as input or output 
> having logical 0 and logical 1 as their values (some other options
> are applicable, but they're not crucial for this explanation).
> Most common usage of GPIO interface is LED and button control for
> various SoCs.

we do much more, since years:  we attach I2C buses over GPIO, or 1-Wire
buses.  GPIO is not just for LEDs.

> Architecture:
> I tried to separate hardware implementation from logic as much as
> possible. All the HW-independent stuff resides in sys/dev/gpio 
> directory. It consists of gpioc (GPIO controller device), 
> gpiobus (bus that manages devices attached to GPIO controller)
> and gpioled (implementation of LED driver that illustrates usage
> pattern of gpiobus, utilizes led(4) interface).
> HW-dependent part might be a part of SoC, I2C extender, whatever.
> It should implement interface defined in sys/dev/gpio/gpio_if.m:
>   gpio_pin_max           - get maximum pin available
>   gpio_pin_getcaps       - get capabilities for given pin
>   gpio_pin_getflags      - get flags for given pin
>   gpio_pin_setflags      - set flags for given pin
>   gpio_pin_getname       - get pin name (if any)
>   gpio_pin_set           - set pin value
>   gpio_pin_get           - get pin value
>   gpio_pin_toggle        - toggle(invert) pin value
> And on attaching HW driver should add gpioc and gpiobus as its
> children.
> gpioc creates /dev/gpiocX entry that is used by gpioctl application 
> for managing GPIO pins using following ioctls:
>   GPIOMAXPIN            - get maximum pin available
>   GPIOGETCONFIG         - get flags/capabilities/name for given pin
>   GPIOSETCONFIG         - set flags for given pin
>   GPIOGET               - get pin value
>   GPIOSET               - set pin value
>   GPIOTOGGLE            - toggle(invert) pin value
> gpioctl usage:
>   gpioctl -f ctldev -l [-v]
>   gpioctl -f ctldev -t pin
>   gpioctl -f ctldev -c pin flag ...
>   gpioctl -f ctldev pin [0|1]
> gpiobus manages devices attached to gpio controller. Its interface
> is a subset of of gpio_if.m interface and allows child devices talk
> to GPIO controller. At the moment children could be set only by hints
> file and pin space is limited to 32. Example:
> # RF led
> hint.gpioled.0.at="gpiobus0"
> hint.gpioled.0.name="rf"
> # pin 2
> hint.gpioled.0.pins=0x0004
> Interface functions:
>   gpiobus_pin_getcaps    - get capabilities for given pin
>   gpiobus_pin_getflags   - get flags for given pin
>   gpiobus_pin_setflags   - set flags for given pin
>   gpiobus_pin_set        - set pin value
>   gpiobus_pin_get        - get pin value
>   gpiobus_pin_toggle     - toggle(invert) pin value
> Reference implementation of child device is sys/dev/gpio/gpioled.c
> It provides on/off function for led(4) API
> Any comments/feedback are welcome

it suffers from the same problems my implementation in other BSD 
suffers:  No interrupt capabilities, no capability to build buses wider 
than 1 bit.

your gpioctl command line syntax is not nice.

I suggest you take a closer look at gpio in NetBSD and that we work 
together on this.  My offer stands.

- Marc

More information about the freebsd-embedded mailing list