[coreboot-gerrit] Change in coreboot[master]: lib/thread: Allow nesting thread_cooperate and thread_prevent_coop

[Raul Rangel (Code Review)]

Raul Rangel has uploaded this change for review. ( https://review.coreboot.org/c/coreboot/+/56350 )

Change subject: lib/thread: Allow nesting thread_cooperate and thread_prevent_coop
......................................................................

lib/thread: Allow nesting thread_cooperate and thread_prevent_coop

This change allows nesting critical sections, and frees the caller from
having to keep track of whether the thread has coop enabled.

I also removed the `thread_cooperate` inside of `idle_thread_init` since
it was really setting up the BSP thread and had nothing to do with the
idle thread.

BUG=b:179699789
TEST=Boot guybrush with SPI DMA

Suggested-by: Julius Werner 
Signed-off-by: Raul E Rangel 
Change-Id: I325ab6181b17c5c084ca1e2c181b4df235020557
---
M src/include/thread.h
M src/lib/thread.c
2 files changed, 17 insertions(+), 9 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/50/56350/1

diff --git a/src/include/thread.h b/src/include/thread.h
index 6df9d7e..8f12343 100644
--- a/src/include/thread.h
+++ b/src/include/thread.h
@@ -43,8 +43,13 @@

/* Allow and prevent thread cooperation on current running thread. By default
  * all threads are marked to be cooperative. That means a thread can yield
- * to another thread at a pre-determined switch point. Current there is
- * only a single place where switching may occur: a call to udelay(). */
+ * to another thread at a pre-determined switch point. i.e., udelay,
+ * thread_yield, or thread_yield_microseconds.
+ *
+ * These method should be used to guard critical sections so a dead lock does
+ * not occur. The critical sections can be nested. Just make sure the methods
+ * are used in pairs.
+ */
 void thread_cooperate(void);
 void thread_prevent_coop(void);

diff --git a/src/lib/thread.c b/src/lib/thread.c
index a8c0772c..db70b17 100644
--- a/src/lib/thread.c
+++ b/src/lib/thread.c
@@ -31,7 +31,7 @@

static inline int thread_can_yield(const struct thread *t)
 {
-	return (t != NULL && t->can_yield);
+	return (t != NULL && t->can_yield > 0);
 }

/* Assumes current CPU info can switch. */
@@ -213,8 +213,6 @@
    /* Queue idle thread to run once all other threads have yielded. */
    prepare_thread(t, idle_thread, NULL, call_wrapper, NULL);
    push_runnable(t);
-	/* Mark the currently executing thread to cooperate. */
-	thread_cooperate();
 }

/* Don't inline this function so the timeout_callback won't have its storage
@@ -260,6 +258,7 @@
    ci->thread = t;
    t->stack_orig = (uintptr_t)ci;
    t->id = 0;
+	t->can_yield = 1;

stack_top = &thread_stacks[CONFIG_STACK_SIZE] - sizeof(struct cpu_info);
    for (i = 1; i < TOTAL_NUM_THREADS; i++) {
@@ -359,8 +358,10 @@

current = current_thread();

-	if (current != NULL)
-		current->can_yield = 1;
+	if (current == NULL)
+		return;
+
+	current->can_yield++;
 }

void thread_prevent_coop(void)
@@ -369,6 +370,8 @@

current = current_thread();

-	if (current != NULL)
-		current->can_yield = 0;
+	if (current == NULL)
+		return;
+
+	current->can_yield--;
 }