cmos post: Guard with spinlock

The CMOS post code storage mechanism does back-to-back
CMOS reads and writes that may be interleaved during
CPU bringup, leading to corruption of the log or of other
parts of CMOS.

Change-Id: I704813cc917a659fe034b71c2ff9eb9b80f7c949
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/58102
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: http://review.coreboot.org/4227
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/x86/include/arch/smp/spinlock.h

@@ -1,6 +1,8 @@
 #ifndef ARCH_SMP_SPINLOCK_H
 #define ARCH_SMP_SPINLOCK_H
 
+#ifndef __PRE_RAM__
+
 /*
  * Your basic SMP spinlocks, allowing only a single CPU anywhere
  */
@@ -61,4 +63,16 @@ static inline __attribute__((always_inline)) void cpu_relax(void)
 	__asm__ __volatile__("rep;nop": : :"memory");
 }
 
+#else /* !__PRE_RAM__ */
+
+#define DECLARE_SPIN_LOCK(x)
+#define barrier()		do {} while(0)
+#define spin_is_locked(lock)	0
+#define spin_unlock_wait(lock)	do {} while(0)
+#define spin_lock(lock)		do {} while(0)
+#define spin_unlock(lock)	do {} while(0)
+#define cpu_relax()		do {} while(0)
+
+#endif /* !__PRE_RAM__ */
+
 #endif /* ARCH_SMP_SPINLOCK_H */

src/console/post.c

@@ -23,6 +23,7 @@
 #include <console/console.h>
 #if CONFIG_CMOS_POST
 #include <pc80/mc146818rtc.h>
+#include <smp/spinlock.h>
 #endif
 #include <elog.h>
 
@@ -44,10 +45,14 @@ void __attribute__((weak)) mainboard_post(uint8_t value)
 
 #if CONFIG_CMOS_POST
 
+DECLARE_SPIN_LOCK(cmos_post_lock)
+
 #if !defined(__PRE_RAM__)
 void cmos_post_log(void)
 {
-	u8 code;
+	u8 code = 0;
+
+	spin_lock(&cmos_post_lock);
 
 	/* Get post code from other bank */
 	switch (cmos_read(CMOS_POST_BANK_OFFSET)) {
@@ -57,10 +62,10 @@ void cmos_post_log(void)
 	case CMOS_POST_BANK_1_MAGIC:
 		code = cmos_read(CMOS_POST_BANK_0_OFFSET);
 		break;
-	default:
-		return;
 	}
 
+	spin_unlock(&cmos_post_lock);
+
 	/* Check last post code in previous boot against normal list */
 	switch (code) {
 	case POST_OS_BOOT:
@@ -80,6 +85,8 @@ void cmos_post_log(void)
 
 static void cmos_post_code(u8 value)
 {
+	spin_lock(&cmos_post_lock);
+
 	switch (cmos_read(CMOS_POST_BANK_OFFSET)) {
 	case CMOS_POST_BANK_0_MAGIC:
 		cmos_write(value, CMOS_POST_BANK_0_OFFSET);
@@ -88,6 +95,8 @@ static void cmos_post_code(u8 value)
 		cmos_write(value, CMOS_POST_BANK_1_OFFSET);
 		break;
 	}
+
+	spin_unlock(&cmos_post_lock);
 }
 #endif /* CONFIG_CMOS_POST */