common: introduce bthreads, co-operative barebox threads

With the new setjmp/longjmp/initjmp support, we have all the
architecture support in place to have suspendable green
threads in barebox. These are expected to replace pollers and
workqueues. For now we still have a differentiation between
the main and secondary threads. The main thread is allowed
I/O access unconditionally. If it's in a delay loop, a secondary
thread running needs to be wary of not entering the same driver
and doing hardware manipulation. We already have slices as
mechanism to guard against this, but they aren't used as widely
as needed.

Preferably, in the end, threads will automatically yield until
they can claim a resource (i.e. lock a mutex). Until we are there,
take the same care when using bthreads as with pollers.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

4 files changed, 67 insertions, 8 deletions

diff --git a/include/bthread.h b/include/bthread.h
new file mode 100644
index 0000000000..e3871fb115
--- /dev/null
+++ b/include/bthread.h
@@ -0,0 +1,53 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Ahmad Fatoum, Pengutronix
+ */
+
+#ifndef __BTHREAD_H_
+#define __BTHREAD_H_
+
+#include <linux/stddef.h>
+
+struct bthread;
+
+extern struct bthread *current;
+
+struct bthread *bthread_create(int (*threadfn)(void *), void *data, const char *namefmt, ...);
+void bthread_free(struct bthread *bthread);
+
+void bthread_schedule(struct bthread *);
+void bthread_wake(struct bthread *bthread);
+void bthread_suspend(struct bthread *bthread);
+int bthread_should_stop(void);
+int bthread_stop(struct bthread *bthread);
+void bthread_info(void);
+const char *bthread_name(struct bthread *bthread);
+bool bthread_is_main(struct bthread *bthread);
+
+/**
+ * bthread_run - create and wake a thread.
+ * @threadfn: the function to run for coming reschedule cycles
+ * @data: data ptr for @threadfn.
+ * @namefmt: printf-style name for the thread.
+ *
+ * Description: Convenient wrapper for bthread_create() followed by
+ * bthread_wakeup().  Returns the bthread or NULL
+ */
+#define bthread_run(threadfn, data, namefmt, ...)                          \
+({                                                                         \
+        struct bthread *__b                                                \
+                = bthread_create(threadfn, data, namefmt, ## __VA_ARGS__); \
+        if (__b)							   \
+                bthread_wake(__b);                                         \
+        __b;                                                               \
+})
+
+#ifdef CONFIG_BTHREAD
+void bthread_reschedule(void);
+#else
+static inline void bthread_reschedule(void)
+{
+}
+#endif
+
+#endif
diff --git a/include/poller.h b/include/poller.h
index db773265b2..371dafc6f8 100644
--- a/include/poller.h
+++ b/include/poller.h
@@ -39,6 +39,8 @@ static inline bool poller_async_active(struct poller_async *pa)
 	return pa->active;
 }
 
+extern int poller_active;
+
 #ifdef CONFIG_POLLER
 void poller_call(void);
 #else
diff --git a/include/sched.h b/include/sched.h
index 43d239c3ef..57be1678fd 100644
--- a/include/sched.h
+++ b/include/sched.h
@@ -2,11 +2,14 @@
 #ifndef __BAREBOX_SCHED_H_
 #define __BAREBOX_SCHED_H_
 
+#include <bthread.h>
 #include <poller.h>
 
 static inline void resched(void)
 {
 	poller_call();
+	if (!IS_ENABLED(CONFIG_POLLER) || !poller_active)
+		bthread_reschedule();
 }
 
 #endif
diff --git a/include/slice.h b/include/slice.h
index b2d65b80cd..cf684300a8 100644
--- a/include/slice.h
+++ b/include/slice.h
@@ -1,6 +1,8 @@
 #ifndef __SLICE_H
 #define __SLICE_H
 
+#include <bthread.h>
+
 enum slice_action {
 	SLICE_ACQUIRE = 1,
 	SLICE_RELEASE = -1,
@@ -35,12 +37,11 @@ void command_slice_release(void);
 
 extern int poller_active;
 
-#ifdef CONFIG_POLLER
-#define assert_command_context() ({    \
-	WARN_ONCE(poller_active, "%s called in poller\n", __func__); \
-})
-#else
-#define assert_command_context() do { } while (0)
-#endif
+#define assert_command_context() do { \
+	WARN_ONCE(IS_ENABLED(CONFIG_POLLER) && poller_active, \
+		  "%s called in poller\n", __func__); \
+	WARN_ONCE(IS_ENABLED(CONFIG_BTHREAD) && !bthread_is_main(current), \
+		  "%s called in secondary bthread\n", __func__); \
+} while (0)
 
-#endif /* __SLICE_H */
+#endif