On 14.02.25 15:00, Jerome Forissier wrote:
Add an 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. 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() is passed zero for the stack_sz argument.
The implementation is based on context-switching via initjmp()/setjmp()/
longjmp() and is inspired from barebox threads [1].
[1] https://github.com/barebox/barebox/blob/master/common/bthread.c
Signed-off-by: Jerome Forissier <jerome.foriss...@linaro.org>
---
include/uthread.h | 31 ++++++++++++++
lib/Kconfig | 19 ++++++++
lib/Makefile | 2 +
lib/uthread.c | 107 ++++++++++++++++++++++++++++++++++++++++++++++
4 files changed, 159 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..ea1389e82c6
--- /dev/null
+++ b/include/uthread.h
@@ -0,0 +1,31 @@
+/* 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);
+void uthread_free_all(void);
+/* Returns false when all threads are done */
+bool uthread_schedule(void);
+
+#else
+
+static inline int uthread_create(void (*fn)(void *), void *arg, size_t
stack_sz)
+{
+ fn(arg);
+ return 0;
+}
+
+static inline void uthread_free_all(void) { }
+
+static inline bool uthread_schedule(void) { return false; }
+
+#endif /* CONFIG_UTHREAD */
+#endif /* _UTHREAD_H_ */
diff --git a/lib/Kconfig b/lib/Kconfig
index 1a683dea670..c3416bbd0be 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -1255,6 +1255,25 @@ 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 32168
+ help
+ The default stask size for uthreads. Each uthread has its own stack.
+
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..bb132001fb6
--- /dev/null
+++ b/lib/uthread.c
@@ -0,0 +1,107 @@
+// 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;
+ struct list_head list;
+} main_thread = {
+ .list = LIST_HEAD_INIT(main_thread.list),
+};
+
+static struct uthread *current = &main_thread;
+
+static void __noreturn uthread_trampoline(void)
+{
+ current->fn(current->arg);
+ current->done = true;
+ current = &main_thread;
+ longjmp(current->ctx, 1);
+ /* Not reached */
+ while (true)
+ ;
+}
+
+static void uthread_free(struct uthread *uthread)
+{
+ if (!uthread)
+ return;
+ free(uthread->stack);
+ free(uthread);
+}
+
+int uthread_create(void (*fn)(void *), void *arg, size_t stack_sz)
+{
+ 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;
+
+ list_add_tail(&uthread->list, ¤t->list);
+
+ initjmp(uthread->ctx, uthread_trampoline, uthread->stack + stack_sz);
+
+ return 0;
+err:
+ uthread_free(uthread);
+ return -1;
+}
+
+void uthread_free_all(void)
+{
+ struct uthread *next;
+ struct uthread *tmp;
+
+ list_for_each_entry_safe(next, tmp, ¤t->list, list) {
+ list_del(&next->list);
+ uthread_free(next);
+ }
+}
+
For every function, please, create a Sphinx style documentation.
For the whole uthread library, please, create a document in
/doc/develop/ explaining how to use the API functions.
Best regards
Heinrich
+static void uthread_resume(struct uthread *uthread)
+{
+ if (!setjmp(current->ctx)) {
+ current = uthread;
+ longjmp(uthread->ctx, 1);
+ }
+}
+
+bool uthread_schedule(void)
+{
+ struct uthread *next;
+
+ list_for_each_entry(next, ¤t->list, list) {
+ if (!next->done) {
+ uthread_resume(next);
+ return true;
+ }
+ }
+ return false;
+}
