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>

1 files changed, 8 insertions, 0 deletions

diff --git a/common/Kconfig b/common/Kconfig
index c0ff57bcdb..b1f4543e03 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -960,6 +960,14 @@ config BAREBOXCRC32_TARGET
 config POLLER
 	bool "generic polling infrastructure"
 
+config BTHREAD
+	bool "barebox co-operative (green) thread infrastructure"
+	depends on HAS_ARCH_SJLJ
+	help
+	 barebox threads are lightweight cooperative (green) threads that are
+	 scheduled within delay loops and the console idle to asynchronously
+	 execute actions, like checking for link up or feeding a watchdog.
+
 config STATE
 	bool "generic state infrastructure"
 	select CRC32