mec1322: Add support for CONFIG_WATCHDOG_HELP

If CONFIG_WATCHDOG_HELP is defined, a 16-bit timer is used as an
auxiliary timer to interrupt us 50ms before the watchdog expires. When
the auxiliary timer expires, the stack trace is printed. Watchdog then
expires 50ms after and reboots the system.

BUG=chrome-os-partner:24107
TEST=Define CONFIG_WATCHDOG_HELP, and see stack trace on 'waitms 2000'.
TEST=Undefine CONFIG_WATCHDOG_HELP, and check watchdog still works
without printing stack trace.
BRANCH=None

Change-Id: I2555d3f86a15c83bb03a00c6807f77d9dddaf333
Signed-off-by: Vic (Chun-Ju) Yang <victoryang@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/178284
Reviewed-by: Vincent Palatin <vpalatin@chromium.org>

2 files changed, 82 insertions, 5 deletions

diff --git a/board/mec1322_evb/board.h b/board/mec1322_evb/board.h
index c5f14a27f9..ab0c734657 100644
--- a/board/mec1322_evb/board.h
+++ b/board/mec1322_evb/board.h
@@ -10,6 +10,7 @@
 
 /* Optional features */
 #define CONFIG_SYSTEM_UNLOCKED  /* Allow dangerous commands */
+#define CONFIG_WATCHDOG_HELP
 
 /* Modules we want to exclude */
 #undef CONFIG_EEPROM
diff --git a/chip/mec1322/watchdog.c b/chip/mec1322/watchdog.c
index f46360f152..87533ac571 100644
--- a/chip/mec1322/watchdog.c
+++ b/chip/mec1322/watchdog.c
@@ -5,23 +5,70 @@
 
 /* Watchdog driver */
 
-/*
- * TODO(crosbug.com/p/24107): Use independent timer for warning before watchdog
- *                            timer expires.
- */
-
 #include "hooks.h"
 #include "registers.h"
+#include "task.h"
 #include "watchdog.h"
 
+/*
+ * Fire auxiliary timer 50ms before watchdog timer expires. This leaves
+ * some time for debug trace to be printed.
+ */
+#define AUX_TIMER_PERIOD_MS (WATCHDOG_PERIOD_MS - 50)
+
 void watchdog_reload(void)
 {
 	MEC1322_WDG_KICK = 1;
+
+#ifdef CONFIG_WATCHDOG_HELP
+	/* Reload the auxiliary timer */
+	MEC1322_TMR16_CTL(0) &= ~(1 << 5);
+	MEC1322_TMR16_CNT(0) = AUX_TIMER_PERIOD_MS;
+	MEC1322_TMR16_CTL(0) |= 1 << 5;
+#endif
 }
 DECLARE_HOOK(HOOK_TICK, watchdog_reload, HOOK_PRIO_DEFAULT);
 
 int watchdog_init(void)
 {
+#ifdef CONFIG_WATCHDOG_HELP
+	uint32_t val;
+
+	/*
+	 * Watchdog does not warn us before expiring. Let's use a 16-bit
+	 * timer as an auxiliary timer.
+	 */
+
+	/* Stop the auxiliary timer if it's running */
+	MEC1322_TMR16_CTL(0) &= ~(1 << 5);
+
+	/* Enable auxiliary timer */
+	MEC1322_TMR16_CTL(0) |= 1 << 0;
+
+	val = MEC1322_TMR16_CTL(0);
+
+	/* Pre-scale = 48000 -> 1kHz -> Period = 1ms */
+	val = (val & 0xffff) | (47999 << 16);
+
+	/* No auto restart */
+	val &= ~(1 << 3);
+
+	/* Count down */
+	val &= ~(1 << 2);
+
+	MEC1322_TMR16_CTL(0) = val;
+
+	/* Enable interrupt from auxiliary timer */
+	MEC1322_TMR16_IEN(0) |= 1;
+	task_enable_irq(MEC1322_IRQ_TIMER16_0);
+	MEC1322_INT_ENABLE(23) |= 1 << 0;
+	MEC1322_INT_BLK_EN |= 1 << 23;
+
+	/* Load and start the auxiliary timer */
+	MEC1322_TMR16_CNT(0) = AUX_TIMER_PERIOD_MS;
+	MEC1322_TMR16_CNT(0) |= 1 << 5;
+#endif
+
 	/* Set timeout. It takes 1007us to decrement WDG_CNT by 1. */
 	MEC1322_WDG_LOAD = WATCHDOG_PERIOD_MS * 1000 / 1007;
 
@@ -30,3 +77,32 @@ int watchdog_init(void)
 
 	return EC_SUCCESS;
 }
+
+#ifdef CONFIG_WATCHDOG_HELP
+void watchdog_check(uint32_t excep_lr, uint32_t excep_sp)
+{
+	/* Clear status */
+	MEC1322_TMR16_STS(0) |= 1;
+
+	watchdog_trace(excep_lr, excep_sp);
+}
+
+void IRQ_HANDLER(MEC1322_IRQ_TIMER16_0)(void) __attribute__((naked));
+void IRQ_HANDLER(MEC1322_IRQ_TIMER16_0)(void)
+{
+	/* Naked call so we can extract raw LR and SP */
+	asm volatile("mov r0, lr\n"
+		     "mov r1, sp\n"
+		     /* Must push registers in pairs to keep 64-bit aligned
+		      * stack for ARM EABI.  This also conveninently saves
+		      * R0=LR so we can pass it to task_resched_if_needed. */
+		     "push {r0, lr}\n"
+		     "bl watchdog_check\n"
+		     "pop {r0, lr}\n"
+		     "b task_resched_if_needed\n");
+}
+const struct irq_priority IRQ_PRIORITY(MEC1322_IRQ_TIMER16_0)
+	__attribute__((section(".rodata.irqprio")))
+		= {MEC1322_IRQ_TIMER16_0, 0}; /* put the watchdog at the
+						 highest priority */
+#endif