Documentation/ABI/testing/configfs-thunderbolt_stream

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		Configuration group for a stream Thunderbolt/USB4
		service. It is possible to create groups even if there
		is no connection yet to the other host. Once a
		connection established and there is stream service on
		the remote side that matches, this configuration is
		applied to it.

		To find the service name you can run tblist from tbtools [1]:

		  # tblist -A
		  ...
		  Domain 0 Route 3 Index 0: stream

		[1] https://github.com/intel/tbtools

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		Creates new stream with $name and fills it with the
		default values. If there is an advertised remote stream
		with the same name, uses its values as the default.

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name/busy_poll
Date:		Nov 2026
KernelVersion:	v7.3
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		Instead of using interrupts for completing the frames in
		the TX/RX rings, busy poll them directly from the
		read(2) and write(2) calls. This burns more CPU cycles
		but provides lower latency for applications that need it.

		This also makes poll(2) return EPOLLERR because
		interrupts do not provide wakeup anymore. Likewise a
		blocking read(2) without available data busy-spins until
		data arrives or a signal is received.

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name/index
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		This matches the X in /dev/tbstreamX and allows userspace
		to map the configfs directory to the corresponding character
		device.

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name/in_hopid
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		In HopID used with the read path of the tunnel. Available HopIDs
		for tunneling start from 8. You can pass also -1 for automatic
		allocation. The allocated value can be read here. Writing 0 will
		de-allocate if the stream is not in use.

		To figure out the maximum HopID you can run tbget from
		tbtools for the lane adapter. For example below we check
		for lane adapter number 1 (first USB4 port):

		  # tbget -r 0 -a 1 -D ADP_CS_5.Max\ Input\ HopID
		  19

		This allows to use anything between 8 and 19 inclusive.

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name/out_hopid
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		Out HopID used with the write path of the tunnel. Available HopIDs
		for tunneling start from 8. You can pass also -1 for automatic
		allocation. The allocated value can be read here. Writing 0 will
		de-allocate if the stream is not in use. See @in_hopid
		for how to figure out the maximum HopID.

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name/ring_size
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		Size of the TX/RX rings. Can be adjusted between 32 and
		4096. The default is 256.

What:		/sys/kernel/config/thunderbolt/stream/<xdomain>.<service>/$name/throttling
Date:		Sep 2026
KernelVersion:	v7.2
Contact:	Mika Westerberg <mika.westerberg@linux.intel.com>
Description:
		Interrupt throttling rate in ns. Lower values can give
		better latency. The default is 8192 ns.