vhost-device-scmi

This program is a vhost-user backend for a VirtIO SCMI device. It provides SCMI access to various entities on the host; not necessarily only those providing an SCMI interface themselves.

It is tested with QEMU's -device vhost-user-scmi-pci but should work with any virtual machine monitor (VMM) that supports vhost-user. See the Examples section below.

Synopsis

vhost-device-scmi [OPTIONS]

Options

.. program:: vhost-device-scmi

.. option:: -h, --help

Print help.

.. option:: -s, --socket-path=PATH

Location of the vhost-user Unix domain sockets.

.. option:: -d, --device=SPEC

SCMI device specification in the format ID,PROPERTY=VALUE,....
For example: -d iio,path=/sys/bus/iio/devices/iio:device0,channel=in_accel.
Can be used multiple times for multiple exposed devices. If no device is specified then no device will be provided to the guest OS but VirtIO SCMI will be still available there. Use --help-devices to list help on all the available devices.

You can set RUST_LOG environment variable to debug to get maximum messages on the standard error output.

Examples

The daemon should be started first:

::

host# vhost-device-scmi --socket-path=scmi.sock --device fake,name=foo

The QEMU invocation needs to create a chardev socket the device can use to communicate as well as share the guests memory over a memfd:

::

host# qemu-system
-chardev socket,path=scmi.sock,id=scmi
-device vhost-user-scmi-pci,chardev=vscmi,id=scmi
-machine YOUR-MACHINE-OPTIONS,memory-backend=mem
-m 4096
-object memory-backend-file,id=mem,size=4G,mem-path=/dev/shm,share=on
...

Supported SCMI protocols

The currently supported SCMI protocols are:

• base
• sensor management

Basically only the mandatory and necessary parts of the protocols are implemented.

See source code (scmi crate) documentation for details and how to add more protocols, host device bindings or other functionality.

Testing

SCMI is supported only on Arm in Linux. This restriction doesn't apply to the host, which can be any architecture as long as the guest is Arm.

The easiest way to test it on the guest side is using the Linux SCMI Industrial I/O driver there. If an 3-axes accelerometer or gyroscope VirtIO SCMI device is present and the guest kernel is compiled with CONFIG_IIO_SCMI enabled then the device should be available in /sys/bus/iio/devices/. The vhost-device-scmi fake device is suitable for this.

Of course, other means of accessing SCMI devices can be used too. The following Linux kernel command line can be useful to obtain SCMI trace information, in addition to SCMI related messages in dmesg: trace_event=scmi:* ftrace=function ftrace_filter=scmi*.

Kernel support for testing

kernel subdirectory contains instructions how to create emulated industrial I/O devices for testing.

License

This project is licensed under either of

• Apache License, Version 2.0
• BSD-3-Clause License

unless specified in particular files otherwise.