charge_state_v2: Throttle AP in low battery voltage

When EC sees voltage drops below BAT_LOW_VOLTAGE_THRESH,
we kick off a timer and ask AP to throttle.

When the timer expires which means EC hasn't seen under-voltage
for BAT_UVP_TIMEOUT_US, we ask AP to stop throttling.

We reset the throttling status and do nothing when AP is off (S5).

BUG=b:73050145, chromium:838754
BRANCH=scarlet
TEST=manually test on scarlet, confirm EC sends
EC_HOST_EVENT_THROTTLE_START and EC_HOST_EVENT_THROTTLE_STOP
host events when entering/exiting UVP.

Change-Id: Ia760989f760f95549f7a8a8acb1d01de23feab5a
Signed-off-by: Philip Chen <philipchen@google.com>
Reviewed-on: https://chromium-review.googlesource.com/1064983
Commit-Ready: Philip Chen <philipchen@chromium.org>
Tested-by: Philip Chen <philipchen@chromium.org>
Reviewed-by: David Schneider <dnschneid@chromium.org>
Reviewed-by: Nicolas Boichat <drinkcat@chromium.org>

4 files changed, 56 insertions, 3 deletions

diff --git a/common/build.mk b/common/build.mk
index 1a0f27e5bf..d64288b5ff 100644
--- a/common/build.mk
+++ b/common/build.mk
@@ -109,6 +109,7 @@ common-$(CONFIG_TABLET_MODE)+=tablet_mode.o
 common-$(CONFIG_TEMP_SENSOR)+=temp_sensor.o
 common-$(CONFIG_THROTTLE_AP)+=thermal.o throttle_ap.o
 common-$(CONFIG_THROTTLE_AP_ON_BAT_DISCHG_CURRENT)+=throttle_ap.o
+common-$(CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE)+=throttle_ap.o
 common-$(CONFIG_TPM_I2CS)+=i2cs_tpm.o
 common-$(CONFIG_TPM_LOGGING)+=event_log.o tpm_log.o
 common-$(CONFIG_U2F)+=u2f.o
diff --git a/common/charge_state_v2.c b/common/charge_state_v2.c
index f237e84bc1..28ec48c3b0 100644
--- a/common/charge_state_v2.c
+++ b/common/charge_state_v2.c
@@ -55,6 +55,14 @@
 	(BAT_MAX_DISCHG_CURRENT * BAT_OCP_HYSTERESIS_PCT / 100) /* mA */
 #endif /* CONFIG_THROTTLE_AP_ON_BAT_DISCHG_CURRENT */
 
+#ifdef CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE
+#ifndef CONFIG_HOSTCMD_EVENTS
+#error "CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE needs CONFIG_HOSTCMD_EVENTS"
+#endif /* CONFIG_HOSTCMD_EVENTS */
+#define BAT_UVP_TIMEOUT_US (60 * SECOND)
+static timestamp_t uvp_throttle_start_time;
+#endif /* CONFIG_THROTTLE_AP_ON_BAT_OLTAGE */
+
 static int charge_request(int voltage, int current);
 
 /*
@@ -1320,7 +1328,7 @@ static int shutdown_on_critical_battery(void)
  * host events. We send these even if the AP is off, since the AP will read and
  * discard any events it doesn't care about the next time it wakes up.
  */
-static void notify_host_of_low_battery(void)
+static void notify_host_of_low_battery_charge(void)
 {
 	/* We can't tell what the current charge is. Assume it's okay. */
 	if (curr.batt.flags & BATT_FLAG_BAD_STATE_OF_CHARGE)
@@ -1343,6 +1351,29 @@ static void set_charge_state(enum charge_state_v2 state)
 	curr.state = state;
 }
 
+static void notify_host_of_low_battery_voltage(void)
+{
+#ifdef CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE
+	if ((curr.batt.flags & BATT_FLAG_BAD_VOLTAGE) ||
+	    chipset_in_state(CHIPSET_STATE_ANY_OFF))
+		return;
+
+	if (curr.batt.voltage < BAT_LOW_VOLTAGE_THRESH) {
+		if (!uvp_throttle_start_time.val) {
+			throttle_ap(THROTTLE_ON, THROTTLE_SOFT,
+				    THROTTLE_SRC_BAT_VOLTAGE);
+		}
+		uvp_throttle_start_time = get_time();
+	} else if (uvp_throttle_start_time.val &&
+		   (get_time().val > uvp_throttle_start_time.val +
+		     BAT_UVP_TIMEOUT_US)) {
+		throttle_ap(THROTTLE_OFF, THROTTLE_SOFT,
+			    THROTTLE_SRC_BAT_VOLTAGE);
+		uvp_throttle_start_time.val = 0;
+	}
+#endif
+}
+
 static void notify_host_of_over_current(struct batt_params *batt)
 {
 #ifdef CONFIG_THROTTLE_AP_ON_BAT_DISCHG_CURRENT
@@ -1400,6 +1431,16 @@ DECLARE_HOOK(HOOK_AC_CHANGE, charge_wakeup, HOOK_PRIO_DEFAULT);
 DECLARE_HOOK(HOOK_CHIPSET_STARTUP, board_base_reset, HOOK_PRIO_DEFAULT);
 #endif
 
+#ifdef CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE
+static void bat_low_voltage_throttle_reset(void)
+{
+	uvp_throttle_start_time.val = 0;
+}
+DECLARE_HOOK(HOOK_CHIPSET_SHUTDOWN,
+	     bat_low_voltage_throttle_reset,
+	     HOOK_PRIO_DEFAULT);
+#endif
+
 static int get_desired_input_current(enum battery_present batt_present,
 				     const struct charger_info * const info)
 {
@@ -1702,7 +1743,8 @@ wait_for_it:
 		/* Wait on the dynamic info until the static info is good. */
 		if (!need_static)
 			update_dynamic_battery_info();
-		notify_host_of_low_battery();
+		notify_host_of_low_battery_charge();
+		notify_host_of_low_battery_voltage();
 
 		/* And the EC console */
 		is_full = calc_is_full();
diff --git a/include/config.h b/include/config.h
index 4511fb39ea..3264ffa195 100644
--- a/include/config.h
+++ b/include/config.h
@@ -2634,6 +2634,14 @@
 #undef CONFIG_THROTTLE_AP_ON_BAT_DISCHG_CURRENT
 
 /*
+ * Throttle the CPU when battery voltage drops below a defined threshold
+ * where the board still boots but some components don't function perfectly.
+ * When this feature is enabled, BAT_LOW_VOLTAGE_THRESH must be defined in
+ * board.h.
+ */
+#undef CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE
+
+/*
  * If defined, dptf is enabled to manage thermals.
  *
  * NOTE: This doesn't mean that thermal control is completely taken care by
diff --git a/include/throttle_ap.h b/include/throttle_ap.h
index db651c432e..a149207667 100644
--- a/include/throttle_ap.h
+++ b/include/throttle_ap.h
@@ -31,6 +31,7 @@ enum throttle_type {
 enum throttle_sources {
 	THROTTLE_SRC_THERMAL = 0,
 	THROTTLE_SRC_BAT_DISCHG_CURRENT,
+	THROTTLE_SRC_BAT_VOLTAGE,
 };
 
 /**
@@ -44,7 +45,8 @@ enum throttle_sources {
  * @param source        Which task is requesting throttling
  */
 #if defined(CONFIG_THROTTLE_AP) || \
-	defined(CONFIG_THROTTLE_AP_ON_BAT_DISCHG_CURRENT)
+	defined(CONFIG_THROTTLE_AP_ON_BAT_DISCHG_CURRENT) || \
+	defined(CONFIG_THROTTLE_AP_ON_BAT_VOLTAGE)
 
 void throttle_ap(enum throttle_level level,
 		 enum throttle_type type,