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docs: admin-guide: thunderbolt: Add instructions how to use USB4STREAM

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Add instructions how USB4STREAM can be configured and used.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
This commit is contained in:
Mika Westerberg
2026-05-06 09:46:58 +03:00
parent 6db21d817b
commit af8922ffb3
1 changed files with 61 additions and 0 deletions
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61
Documentation/admin-guide/thunderbolt.rst
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@@ -373,6 +373,67 @@ port which are named like ``thunderbolt0`` and so on. From this point
you can either use standard userspace tools like ``ip`` to
configure the interface or let your GUI handle it automatically.
Streaming data directly over Thunderbolt cable
----------------------------------------------
In addition to Thunderbolt networking (aka. USB4NET) Linux supports
streaming data directly over a cable as well (aka. USB4STREAM). This is
possible through ``thunderbolt-stream`` driver.
Similarly to ``thunderbolt-net`` you load the driver first on one end::
host1 # modprobe thunderbolt-stream
Then you configure it via ``ConfigFS``::
host1 # cd /sys/kernel/config/thunderbolt/stream
host1 # mkdir -p 0-1.0/data
host1 # cd 0-1.0
host1 # echo -1 > data/in_hopid
host1 # echo -1 > data/out_hopid
This information is automatically announced to the other side via
XDomain properties so if you have cable connected the other side knows
that there is a stream named ``data`` available and can configure it for
you automatically::
host2 # cd /sys/kernel/config/thunderbolt/stream
host2 # mkdir -p 0-3.0/data
Here we used auto-configuration but you can configure it manually too.
In that case you need to fill ``in_hopid`` and ``out_hopid`` accordingly.
If you set them to ``-1`` the next available HopID is used which is
typically what we want.
Once they are configured you can use ``/dev/tbstreamX`` on both sides to
transfer data::
host2 # cat /dev/tbstream0
host1 # dmesg > /dev/tbstream0
Once you are done with the stream you can remove them::
host2 # cd /sys/kernel/config/thunderbolt/stream
host2 # rmdir -p 0-1.0/data
host1 # cd /sys/kernel/config/thunderbolt/stream
host1 # rmdir -p 0-3.0/data
Since streams are essentially files you can use any existing application
that supports ``read(2)`` and ``write(2)`` in some form.
It is possible to have more than one stream and you can have both stream
and ``thunderbolt-net`` in use simultaneously. For example we can create
two streams with name ``control`` and ``data`` like this::
host1 # cd /sys/kernel/config/thunderbolt/stream
host1 # mkdir 0-1.0
host1 # cd 0-1.0
host1 # mkdir control
host1 # mkdir data
Then you have ``/dev/tbstream0`` for ``control`` and ``/dev/tbstream1``
for ``data``. Before you can use them you need to configure them as
shown above for the one stream case.
Forcing power
-------------
Many OEMs include a method that can be used to force the power of a