Merge patch series "Uthreads"

Jerome Forissier <jerome.forissier@linaro.org> says:

This series introduces threads and uses them to improve the performance
of the USB bus scanning code and to implement background jobs in the
shell via two new commands: 'spawn' and 'wait'.

The threading framework is called 'uthread' and is inspired from the
barebox threads [2]. setjmp() and longjmp() are used to save and
restore contexts, as well as a non-standard extension called initjmp().
This new function is added in several patches, one for each
architecture that supports HAVE_SETJMP. A new symbol is defined:
HAVE_INITJMP. Two tests, one for initjmp() and one for the uthread
scheduling, are added to the lib suite.

After introducing threads and making schedule() and udelay() a thread
re-scheduling point, the USB stack initialization is modified to benefit
from concurrency when UTHREAD is enabled, where uthreads are used in
usb_init() to initialize and scan multiple busses at the same time.
The code was tested on arm64 and arm QEMU with 4 simulated XHCI buses
and some devices. On this platform the USB scan takes 2.2 s instead of
5.6 s. Tested on i.MX93 EVK with two USB hubs, one ethernet adapter and
one webcam on each, "usb start" takes 2.4 s instead of 4.6 s.

Finally, the spawn and wait commands are introduced, allowing the use of
threads from the shell. Tested on the i.MX93 EVK with a spinning HDD
connected to USB1 and the network connected to ENET1. The USB plus DHCP
init sequence "spawn usb start; spawn dhcp; wait" takes 4.5 seconds
instead of 8 seconds for "usb start; dhcp".

[1] https://patchwork.ozlabs.org/project/uboot/list/?series=446674
[2] https://github.com/barebox/barebox/blob/master/common/bthread.c

Link: https://lore.kernel.org/r/20250418141114.2056981-1-jerome.forissier@linaro.org

3 files changed, 41 insertions, 0 deletions

diff --git a/doc/api/index.rst b/doc/api/index.rst
index a108718ea99..506843ed74a 100644
--- a/doc/api/index.rst
+++ b/doc/api/index.rst
@@ -25,6 +25,8 @@ U-Boot API documentation
    rng
    sandbox
    serial
+   setjmp
    sysreset
    timer
    unicode
+   uthread
diff --git a/doc/api/setjmp.rst b/doc/api/setjmp.rst
new file mode 100644
index 00000000000..c30e51c2b55
--- /dev/null
+++ b/doc/api/setjmp.rst
@@ -0,0 +1,20 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Long jump API
+=============
+
+.. kernel-doc:: include/setjmp.h
+   :doc: Overview
+
+.. kernel-doc:: include/setjmp.h
+   :internal:
+
+Example
+-------
+
+Here is an example showing how to use the a long jump functions and
+initjmp() in particular:
+
+.. literalinclude:: ../../test/lib/initjmp.c
+   :language: c
+   :linenos:
diff --git a/doc/api/uthread.rst b/doc/api/uthread.rst
new file mode 100644
index 00000000000..8b25cc1ff80
--- /dev/null
+++ b/doc/api/uthread.rst
@@ -0,0 +1,19 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Uthread API
+===========
+
+.. kernel-doc:: include/uthread.h
+   :doc: Overview
+
+.. kernel-doc:: include/uthread.h
+   :internal:
+
+Example
+-------
+
+Here is an example of how to use this API:
+
+.. literalinclude:: ../../test/lib/uthread.c
+   :language: c
+   :linenos: