[coreboot-gerrit] Change in coreboot[master]: cpu/x86/mp_init.c: Add wait_finished_mp_run_on_all_cpus

[Arthur Heymans (Code Review)]

Attention is currently required from: Arthur Heymans.
Hello Arthur Heymans,

I'd like you to do a code review. Please visit

https://review.coreboot.org/c/coreboot/+/63553

to review the following change.

Change subject: cpu/x86/mp_init.c: Add wait_finished_mp_run_on_all_cpus
......................................................................

cpu/x86/mp_init.c: Add wait_finished_mp_run_on_all_cpus

This functions makes sure that all APs finish executing their call
before continuing to execute code on the BSP.

Change-Id: I70244557bb384739e3bd06de3d8414ec9f4d5f62
Signed-off-by: Arthur Heymans 
---
M src/cpu/x86/mp_init.c
M src/include/cpu/x86/mp.h
2 files changed, 25 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/53/63553/1

diff --git a/src/cpu/x86/mp_init.c b/src/cpu/x86/mp_init.c
index 81c987b..656bc63 100644
--- a/src/cpu/x86/mp_init.c
+++ b/src/cpu/x86/mp_init.c
@@ -1009,6 +1009,27 @@
    return mp_run_on_aps(func, arg, MP_RUN_ON_ALL_CPUS, 1000 * USECS_PER_MSEC);
 }

+/*
+ * mp_run_on_all_cpus() only waits for all APs accept to start
+ * running a function call but does not wait for them to finish it.
+ * APs only accept a new task when the the previous one is finished
+ * so to make sure that the post_cpus_add_romcache() is not overwritten
+ * by an AP thread we do a NOOP call on the APs which will ensure the
+ * previous function actually finished running.
+ */
+static void noop(void *unused)
+{
+}
+
+enum cb_err wait_finished_mp_run_on_all_cpus(void (*func)(void *), void *arg)
+{
+	enum cb_err err = mp_run_on_all_cpus(func, arg);
+	if (err != CB_SUCCESS)
+		return err;
+	err = mp_run_on_all_cpus(noop,  NULL);
+	return err;
+}
+
 enum cb_err mp_park_aps(void)
 {
    struct stopwatch sw;
diff --git a/src/include/cpu/x86/mp.h b/src/include/cpu/x86/mp.h
index 1b4c956..5a1e927 100644
--- a/src/include/cpu/x86/mp.h
+++ b/src/include/cpu/x86/mp.h
@@ -117,6 +117,10 @@
 /* Like mp_run_on_aps() but also runs func on BSP. */
 enum cb_err mp_run_on_all_cpus(void (*func)(void *), void *arg);

+/* Like mp_run_on_all_cpus but make sure all APs finish executing the
+   function call. The time limit on a function call is 1 second. */
+enum cb_err wait_finished_mp_run_on_all_cpus(void (*func)(void *), void *arg);
+
 /*
  * Park all APs to prepare for OS boot. This is handled automatically
  * by the coreboot infrastructure.