[coreboot-gerrit] Change in coreboot[master]: thread: Add mutex

[Raul Rangel (Code Review)]

Raul Rangel has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/56230 )

Change subject: thread: Add mutex
......................................................................

thread: Add mutex

We need a way to protect shared resources. Since we are using cooperative
multitasking the mutex implementation is pretty trivial.

BUG=b:179699789
TEST=Verify thread locks and unlocks

Signed-off-by: Raul E Rangel 
Change-Id: Ife1ac95ec064ebcdd00fcaacec37a06ac52885ff
---
M src/include/thread.h
M src/lib/thread.c
2 files changed, 31 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/30/56230/1

diff --git a/src/include/thread.h b/src/include/thread.h
index 902a7f7..9c68072 100644
--- a/src/include/thread.h
+++ b/src/include/thread.h
@@ -19,6 +19,10 @@
    enum cb_err error;
 };

+struct mutex {
+	bool locked;
+};
+
 #if ENV_RAMSTAGE && CONFIG(COOP_MULTITASKING)

struct thread {
@@ -63,6 +67,9 @@
 /* Wait's until the thread has terminated and returns the error code */
 enum cb_err wait_for_thread(struct thread_handle *handle);

+void mutex_lock(struct mutex *mutex);
+void mutex_unlock(struct mutex *mutex);
+
 static inline void thread_init_cpu_info_non_bsp(struct cpu_info *ci)
 {
    ci->thread = NULL;
@@ -101,6 +108,10 @@

struct cpu_info;
 static inline void thread_init_cpu_info_non_bsp(struct cpu_info *ci) { }
+
+static inline void mutex_lock(struct mutex *mutex) {}
+
+static inline void mutex_unlock(struct mutex *mutex) {}
 #endif

#endif /* THREAD_H_ */
diff --git a/src/lib/thread.c b/src/lib/thread.c
index 671cb3e..f9a3fc6 100644
--- a/src/lib/thread.c
+++ b/src/lib/thread.c
@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */

+#include <assert.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdlib.h>
@@ -394,3 +395,22 @@

return handle->error;
 }
+
+void mutex_lock(struct mutex *mutex)
+{
+	struct stopwatch sw;
+
+	stopwatch_init(&sw);
+
+	while (mutex->locked)
+		thread_yield_microseconds(10);
+	mutex->locked = 1;
+
+	printk(BIOS_DEBUG, " took %lu us to acquire mutex\n", stopwatch_duration_usecs(&sw));
+}
+
+void mutex_unlock(struct mutex *mutex)
+{
+	assert(mutex->locked);
+	mutex->locked = 0;
+}