On 2/27/25 10:28 AM, David Jander wrote: > Request for comments on: adding the Linux Motion Control subsystem to the > kernel. > > The Linux Motion Control subsystem (LMC) is a new kernel subsystem and > associated device drivers for hardware devices that control mechanical > motion. Most often these are different types of motors, but can also be > linear actuators for example. This is something that I played around with when I first got into Linux kernel hacking as a hobbyist. It's something I've always wanted to see get upstreamed, so feel free to cc me on any future revisions of this series. I'm very interested. :-) We made drivers for basic DC motors driven by an H-bridge both with and without position feedback and also a driver for hobby-type servo motors. For those interested, there is code [1] and docs [2]. One thing we would do different if doing it over again is use a character device instead of sysfs attributes as the interface for starting/stopping/adjusting actuation. [1]: https://github.com/ev3dev/lego-linux-drivers/tree/ev3dev-stretch/motors [2]: http://docs.ev3dev.org/projects/lego-linux-drivers/en/ev3dev-stretch/motors.html > > This subsystem defines a new UAPI for motion devices on the user-space > side, as well as common functionality for hardware device drivers on the > driver side. > > The UAPI is based on a ioctl() interface on character devices representing > a specific hardware device. The hardware device can control one or more > actuators (motors), which are identified as channels in the UAPI. It is > possible to execute motions on individual channels, or combined > affecting several selected (or all) channels simutaneously. Examples of > coordinated movements of several channels could be the individual axes > of a 3D printer or CNC machine for example. > > On the hardware side, this initial set of patches also includes two drivers > for two different kinds of motors. One is a stepper motor controller > device that containes a ramp generator capable of autonomously executing > controlled motions following a multi-point acceleration profile > (TMC5240), as well as a simple DC motor controller driver that can control > DC motors via a half-bridge or full H-bridge driver such as the TI DRV8873 > for example. > > Towards the IIO subsystem, LMC supports generating iio trigger events that > fire at certain motion events, such as passing a pre-programmed position or > when reaching the motion target position, depending on the capabilities of > the hardware device. This enables for example triggering an ADC measurement > at a certain position during a movement. I would expect to be using the counter subsystem for position, at least in cases where there is something like a quadrature encoder involved. > > In the future, making use of PREEMPT_RT, even dumb STEP/DIR type stepper > motor controller drivers may be implemented entirely in the kernel, > depending on some characteristics of the hardware (latency jittter, > interrupt latency and CPU speed mainly). > > The existence of this subsystem may affect other projects, such as > Linux-CNC and Klipper for example. > > This code is already in use controlling machines with up to 16 stepper > motors and up to 4 DC motors simutaneously. Up to this point the UAPI > has shown to be adequate and sufficient. Careful thought has gone into > the UAPI design to make sure it coveres as many use-cases as possible, > while being versioned and extensible in the future, with backwards > compatibility in mind. > > David Jander (7): > drivers: Add motion control subsystem Would it be too broad to call this an actuation subsystem instead where motion is just one kind of actuation? > motion: Add ADI/Trinamic TMC5240 stepper motor controller > motion: Add simple-pwm.c PWM based DC motor controller driver > Documentation: Add Linux Motion Control documentation > dt-bindings: motion: Add common motion device properties > dt-bindings: motion: Add adi,tmc5240 bindings > dt-bindings: motion: Add motion-simple-pwm bindings >
