On 25.02.25 17:34, Jerome Forissier wrote:
Add an new internal API called uthread (Kconfig symbol: UTHREAD) which
nits:
%s/an/a/
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.foriss...@linaro.org>
---
include/uthread.h | 44 ++++++++++++
lib/Kconfig | 21 ++++++
lib/Makefile | 2 +
lib/uthread.c | 178 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 245 insertions(+)
create mode 100644 include/uthread.h
create mode 100644 lib/uthread.c
diff --git a/include/uthread.h b/include/uthread.h
new file mode 100644
index 00000000000..f1f86d210d5
--- /dev/null
+++ b/include/uthread.h
@@ -0,0 +1,44 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2025 Linaro Limited
+ */
+
+#include <linux/types.h>
+
+#ifndef _UTHREAD_H_
+#define _UTHREAD_H_
+
+#ifdef CONFIG_UTHREAD
+
+int uthread_create(void (*fn)(void *), void *arg, size_t stack_sz,
+ unsigned int grp_id);
Every function needs a Shinx style documentation.
+bool uthread_schedule(void);
+unsigned int uthread_grp_new_id(void);
+bool uthread_grp_done(unsigned int grp_id);
+
+#else
+
+static inline int uthread_create(void (*fn)(void *), void *arg, size_t
stack_sz,
+ unsigned int grp_id)
+{
+ fn(arg);
+ return 0;
+}
+
+static inline bool uthread_schedule(void)
+{
+ return false;
+}
+
+static inline unsigned int uthread_grp_new_id(void)
+{
+ return 0;
+}
+
+static inline bool uthread_grp_done(unsigned int grp_id)
+{
+ return true;
+}
+
+#endif /* CONFIG_UTHREAD */
+#endif /* _UTHREAD_H_ */
diff --git a/lib/Kconfig b/lib/Kconfig
index 1a683dea670..b32740ecbcc 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -1255,6 +1255,27 @@ config PHANDLE_CHECK_SEQ
enable this config option to distinguish them using
phandles in fdtdec_get_alias_seq() function.
+config UTHREAD
+ bool "Enable thread support"
+ depends on HAVE_INITJMP
+ help
+ Implement a simple form of cooperative multi-tasking based on
+ context-switching via initjmp(), setjmp() and longjmp(). The
+ uthread_ interface enables the main thread of execution to create
+ one or more secondary threads and schedule them until they all have
+ returned. At any point a thread may suspend its execution and
+ schedule another thread, which allows for the efficient multiplexing
+ of leghthy operations.
+
+config UTHREAD_STACK_SIZE
+ int "Default uthread stack size"
+ depends on UTHREAD
+ default 32768
+ help
+ The default stak size for uthreads. Each uthread has its own stack.
+ When the stack_sz argument to uthread_create() is zero then this
+ value is used.
+
endmenu
source "lib/fwu_updates/Kconfig"
diff --git a/lib/Makefile b/lib/Makefile
index a7bc2f3134a..3610694de7a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -164,6 +164,8 @@ obj-$(CONFIG_LIB_ELF) += elf.o
obj-$(CONFIG_$(PHASE_)SEMIHOSTING) += semihosting.o
+obj-$(CONFIG_UTHREAD) += uthread.o
+
#
# Build a fast OID lookup registry from include/linux/oid_registry.h
#
diff --git a/lib/uthread.c b/lib/uthread.c
new file mode 100644
index 00000000000..430d1c0de32
--- /dev/null
+++ b/lib/uthread.c
@@ -0,0 +1,178 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2021 Ahmad Fatoum, Pengutronix
+ * Copyright (C) 2025 Linaro Limited
+ *
+ * An implementation of cooperative multi-tasking inspired from barebox threads
+ * https://github.com/barebox/barebox/blob/master/common/bthread.c
+ */
+
+#include <compiler.h>
+#include <asm/setjmp.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <malloc.h>
+#include <stdint.h>
+#include <uthread.h>
+
+static struct uthread {
+ void (*fn)(void *);
+ void *arg;
+ jmp_buf ctx;
+ void *stack;
+ bool done;
+ unsigned int grp_id;
+ struct list_head list;
The structure and all its components need to be documented.
+} main_thread = {
+ .list = LIST_HEAD_INIT(main_thread.list),
+};
+
+static struct uthread *current = &main_thread;
+
+/**
+ * uthread_trampoline() - Call the current thread's entry point then resume the
+ * main thread.
+ *
+ * This is a helper function which is used as the @func argument to the
inijmp()
+ * function, and ultimately invoked via setjmp(). It does not return, but
+ * instead longjmp()'s back to the main thread.
+ */
+static void __noreturn uthread_trampoline(void)
+{
+ struct uthread *curr = current;
+
+ curr->fn(curr->arg);
+ curr->done = true;
+ current = &main_thread;
+ longjmp(current->ctx, 1);
+ /* Not reached */
+ while (true)
+ ;
+}
+
+/**
+ * uthread_free() - Free memory used by a uthread object.
+ */
+static void uthread_free(struct uthread *uthread)
+{
+ if (!uthread)
+ return;
+ free(uthread->stack);
+ free(uthread);
+}
+
+/**
+ * uthread_create() - Create a uthread object and make it ready for execution
+ *
+ * Threads are automatically deleted when then return from their entry point.
+ *
+ * @fn: the thread's entry point
+ * @arg: argument passed to the thread's entry point
+ * @stack_sz: stack size for the new thread (in bytes). The stack is allocated
+ * on the heap.
+ * @grp_id: an optional thread group ID that the new thread should belong to
+ * (zero for no group)
+ */
This documentation should be move to the include and the include needs
to be added to doc/api/.
+int uthread_create(void (*fn)(void *), void *arg, size_t stack_sz,
+ unsigned int grp_id)
We should model the functions more like pthreads.
Let the caller provide struct uthread(). This will allow us to implement
pthread_cancel() and phthread_join().
Best regards
Heinrich
+{
+ struct uthread *uthread;
+
+ if (!stack_sz)
+ stack_sz = CONFIG_UTHREAD_STACK_SIZE;
+
+ uthread = calloc(1, sizeof(*uthread));
+ if (!uthread)
+ return -1;
+
+ uthread->stack = memalign(16, stack_sz);
+ if (!uthread->stack)
+ goto err;
+
+ uthread->fn = fn;
+ uthread->arg = arg;
+ uthread->grp_id = grp_id;
+
+ list_add_tail(&uthread->list, ¤t->list);
+
+ initjmp(uthread->ctx, uthread_trampoline, uthread->stack + stack_sz);
+
+ return 0;
+err:
+ uthread_free(uthread);
+ return -1;
+}
+
+/**
+ * uthread_resume() - switch execution to a given thread
+ *
+ * @uthread: the thread object that should be resumed
+ */
+static void uthread_resume(struct uthread *uthread)
+{
+ if (!setjmp(current->ctx)) {
+ current = uthread;
+ longjmp(uthread->ctx, 1);
+ }
+}
+
+/**
+ * uthread_schedule() - yield the CPU to the next runnable thread
+ *
+ * This function is called either by the main thread or any secondary thread
+ * (that is, any thread created via uthread_create()) to switch execution to
+ * the next runnable thread.
+ *
+ * Return: true if a thread was scheduled, false if no runnable thread was
found
+ */
+bool uthread_schedule(void)
+{
+ struct uthread *next;
+ struct uthread *tmp;
+
+ if (list_empty(¤t->list))
+ return false;
+
+ list_for_each_entry_safe(next, tmp, ¤t->list, list) {
+ if (!next->done) {
+ uthread_resume(next);
+ return true;
+ } else {
+ /* Found a 'done' thread, free its resources */
+ list_del(&next->list);
+ uthread_free(next);
+ }
+ }
+ return false;
+}
+
+/**
+ * uthread_grp_new_id() - return a new ID for a thread group
+ *
+ * Return: the new thread group ID
+ */
+unsigned int uthread_grp_new_id(void)
+{
+ static unsigned int id = 0;
+
+ return ++id;
+}
+
+/**
+ * uthread_grp_done() - test if all threads in a group are done
+ *
+ * @grp: the ID of the thread group that should be considered
+ * Return: false if the group contains at least one runnable thread (i.e., one
+ * thread which entry point has not returned yet), true otherwise
+ */
+bool uthread_grp_done(unsigned int grp_id)
+{
+ struct uthread *next;
+
+ list_for_each_entry(next, &main_thread.list, list) {
+ if (next->grp_id == grp_id && !next->done)
+ return false;
+ }
+
+ return true;
+}
