uthread: add cooperative multi-tasking interface
Add a new internal API called uthread (Kconfig symbol: UTHREAD) which
provides cooperative multi-tasking. The goal is to be able to improve
the performance of some parts of U-Boot by overlapping lengthy
operations, and also implement background jobs in the U-Boot shell.
Each uthread has its own stack allocated on the heap. The default stack
size is defined by the UTHREAD_STACK_SIZE symbol and is used when
uthread_create() receives zero for the stack_sz argument.
The implementation is based on context-switching via initjmp()/setjmp()/
longjmp() and is inspired from barebox threads [1]. A notion of thread
group helps with dependencies, such as when a thread needs to block
until a number of other threads have returned.
The name "uthread" comes from "user-space threads" because the
scheduling happens with no help from a higher privileged mode, contrary
to more complex models where kernel threads are defined. But the 'u'
may as well stand for 'U-Boot' since the bootloader may actually be
running at any privilege level and the notion of user vs. kernel may
not make much sense in this context.
[1] https://github.com/barebox/barebox/blob/master/common/bthread.c
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
diff --git a/doc/api/index.rst b/doc/api/index.rst
index 0dc9ad4..506843ed 100644
--- a/doc/api/index.rst
+++ b/doc/api/index.rst
@@ -29,3 +29,4 @@
sysreset
timer
unicode
+ uthread
diff --git a/doc/api/uthread.rst b/doc/api/uthread.rst
new file mode 100644
index 0000000..21233ff
--- /dev/null
+++ b/doc/api/uthread.rst
@@ -0,0 +1,7 @@
+.. SPDX-License-Identifier: GPL-2.0-or-later
+
+Uthread API
+===========
+
+.. kernel-doc:: include/uthread.h
+ :internal: