> Date: Sat, 14 Dec 2019 10:20:52 +1100
> From: Jonathan Gray <j...@jsg.id.au>
>
> On Fri, Dec 13, 2019 at 10:34:59PM +0100, Patrick Wildt wrote:
> > Hi,
> >
> > I have a ThingM blink(1) USB RGB device that shows up as uhid(4).
> > The tooling is "interesting", especially with all those libusb and
> > HID libraries doing the abstraction. This introduces ublink(4), a
> > dedicated kernel driver for that device. There are two LEDs on the
> > device, which can be modified seperately. The firmware is impress-
> > ive and provides features like playing sequences and adjusting how
> > long it should take to fade from one colour to another. Obviously
> > this also increases the complexity of the tools involved to toggle
> > those RGB LEDs. Thus, the driver is kept simple (for now).
> >
> > In addition to providing a way to set RGB LEDs, we can also use it
> > as a watchdog. If we don't "tickle" it in a specific timeframe it
> > will play a (unless otherwise programmed) random sequence, which for
> > instance can be used to see that the machine has paniced. This has
> > been quite useful while debugging the USB stack, because once the
> > magic sequence started you know that you're in deep trouble. All
> > other features are unimplemented. Gamma correction would be nice
> > to have.
> >
> > Since there is no abstraction layer for LEDs yet, this also intro-
> > duces led(4), which attaches to ublink(4), and provides /dev/ledX.
>
> There is the machdep.led_blink sysctl CPU_LED_BLINK implemented by
> multiple architectures to blink based on load average.
>
> See
> man4.hppa/lcd.4:.Ar machdep.led_blink
> man4.sparc64/auxio.4:.Ar machdep.led_blink
> man4.sparc64/clkbrd.4:.Ar machdep.led_blink
> man4.sparc64/fhc.4:.Ar machdep.led_blink
> man4.sparc64/led.4:.Ar machdep.led_blink
> man4.sparc64/ppm.4:.Ar machdep.led_blink
>
> sys/arch/alpha/include/cpu.h: { "led_blink", CTLTYPE_INT }
> sys/arch/hppa/include/cpu.h: { "led_blink", CTLTYPE_INT },
> sys/arch/landisk/include/cpu.h: { "led_blink", CTLTYPE_INT }
> sys/arch/sparc64/include/cpu.h: { "led_blink", CTLTYPE_INT },
>
Those machines all have a more-or-less dedicated LED for this.
What could be done is to make it possible to assign this function to
arbitrary LEDs through ledctl(8) such that we can have this
functionality on other architectures as well.
As patrick@ is probably aware of, the device trees on various
armv7/arm64 machines have LED devices in them as well. These are
mostly controlled through GPIOs. It'd make sense if the framework
allowed to control these LEDs as well at some point.
