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

1 files changed, 146 insertions, 0 deletions

diff --git a/test/lib/uthread.c b/test/lib/uthread.c
new file mode 100644
index 00000000000..10a94d1c560
--- /dev/null
+++ b/test/lib/uthread.c
@@ -0,0 +1,146 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright 2025 Linaro Limited
+ *
+ * Unit test for uthread
+ */
+
+#include <stdbool.h>
+#include <test/lib.h>
+#include <test/ut.h>
+#include <uthread.h>
+
+static int count;
+
+/* A thread entry point */
+static void worker(void *arg)
+{
+	int loops = (int)(unsigned long)arg;
+	int i;
+
+	for (i = 0; i < loops; i++) {
+		count++;
+		uthread_schedule();
+	}
+}
+
+/*
+ * uthread() - testing the uthread API
+ *
+ * This function creates two threads with the same entry point. The first one
+ * receives 5 as an argument, the second one receives 10. The number indicates
+ * the number of time the worker thread should loop on uthread_schedule()
+ * before returning. The workers increment a global counter each time they loop.
+ * As a result the main thread knows how many times it should call
+ * uthread_schedule() to let the two threads proceed, and it also knows which
+ * value the counter should have at any moment.
+ */
+static int uthread(struct unit_test_state *uts)
+{
+	int i;
+	int id1, id2;
+
+	count = 0;
+	id1 = uthread_grp_new_id();
+	ut_assert(id1 != 0);
+	id2 = uthread_grp_new_id();
+	ut_assert(id2 != 0);
+	ut_assert(id1 != id2);
+	ut_assertok(uthread_create(NULL, worker, (void *)5, 0, id1));
+	ut_assertok(uthread_create(NULL, worker, (void *)10, 0, 0));
+	/*
+	 * The first call is expected to schedule the first worker, which will
+	 * schedule the second one, which will schedule back to the main thread
+	 * (here). Therefore count should be 2.
+	 */
+	ut_assert(uthread_schedule());
+	ut_asserteq(2, count);
+	ut_assert(!uthread_grp_done(id1));
+	/* Four more calls should bring the count to 10 */
+	for (i = 0; i < 4; i++) {
+		ut_assert(!uthread_grp_done(id1));
+		ut_assert(uthread_schedule());
+	}
+	ut_asserteq(10, count);
+	/* This one allows the first worker to exit */
+	ut_assert(uthread_schedule());
+	/* At this point there should be no runnable thread in group 'id1' */
+	ut_assert(uthread_grp_done(id1));
+	/* Five more calls for the second worker to finish incrementing  */
+	for (i = 0; i < 5; i++)
+		ut_assert(uthread_schedule());
+	ut_asserteq(15, count);
+	/* Plus one call to let the second worker return from its entry point */
+	ut_assert(uthread_schedule());
+	/* Now both tasks should be done, schedule should return false */
+	ut_assert(!uthread_schedule());
+
+	return 0;
+}
+LIB_TEST(uthread, 0);
+
+struct mw_args {
+	struct unit_test_state *uts;
+	struct uthread_mutex *m;
+	int flag;
+};
+
+static int mutex_worker_ret;
+
+static int _mutex_worker(struct mw_args *args)
+{
+	struct unit_test_state *uts = args->uts;
+
+	ut_asserteq(-EBUSY, uthread_mutex_trylock(args->m));
+	ut_assertok(uthread_mutex_lock(args->m));
+	args->flag = 1;
+	ut_assertok(uthread_mutex_unlock(args->m));
+
+	return 0;
+}
+
+static void mutex_worker(void *arg)
+{
+	mutex_worker_ret = _mutex_worker((struct mw_args *)arg);
+}
+
+/*
+ * thread_mutex() - testing uthread mutex operations
+ *
+ */
+static int uthread_mutex(struct unit_test_state *uts)
+{
+	struct uthread_mutex m = UTHREAD_MUTEX_INITIALIZER;
+	struct mw_args args = { .uts = uts, .m = &m, .flag = 0 };
+	int id;
+	int i;
+
+	id = uthread_grp_new_id();
+	ut_assert(id != 0);
+	/* Take the mutex */
+	ut_assertok(uthread_mutex_lock(&m));
+	/* Start a thread */
+	ut_assertok(uthread_create(NULL, mutex_worker, (void *)&args, 0,
+				   id));
+	/* Let the thread run for a bit */
+	for (i = 0; i < 100; i++)
+		ut_assert(uthread_schedule());
+	/* Thread should not have set the flag due to the mutex */
+	ut_asserteq(0, args.flag);
+	/* Release the mutex */
+	ut_assertok(uthread_mutex_unlock(&m));
+	/* Schedule the thread until it is done */
+	while (uthread_schedule())
+		;
+	/* Now the flag should be set */
+	ut_asserteq(1, args.flag);
+	/* And the mutex should be available */
+	ut_assertok(uthread_mutex_trylock(&m));
+	ut_assertok(uthread_mutex_unlock(&m));
+
+	/* Of course no error are expected from the thread routine */
+	ut_assertok(mutex_worker_ret);
+
+	return 0;
+}
+LIB_TEST(uthread_mutex, 0);