nereid: bring charger out of LPM on S0 entry

This appears to fix VBUS sourcing, though we don't understand why. It may
also prevent charger damage with as-yet-unexplained cause.

BUG=b:231920135,b:230712704
TEST=VBUS sourcing works when AP is in S0
BRANCH=none

Signed-off-by: Peter Marheine <pmarheine@chromium.org>
Change-Id: Ia4d74f4211eb97b532882914d077e3dde5e59f64
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3686012
Reviewed-by: Andrew McRae <amcrae@google.com>

1 files changed, 47 insertions, 0 deletions

diff --git a/zephyr/projects/nissa/src/nereid/usbc.c b/zephyr/projects/nissa/src/nereid/usbc.c
index 95bb1a5fdc..5219c252e5 100644
--- a/zephyr/projects/nissa/src/nereid/usbc.c
+++ b/zephyr/projects/nissa/src/nereid/usbc.c
@@ -4,6 +4,7 @@
  */
 
 #include <zephyr/logging/log.h>
+#include <ap_power/ap_power.h>
 
 #include "charge_state_v2.h"
 #include "chipset.h"
@@ -80,6 +81,52 @@ __override bool pd_check_vbus_level(int port, enum vbus_level level)
 	return false;
 }
 
+/*
+ * Putting chargers into LPM when in suspend reduces power draw by about 8mW
+ * per charger, but also seems critical to correct operation in source mode:
+ * if chargers are not in LPM when a sink is first connected, VBUS sourcing
+ * works even if the partner is later removed (causing LPM entry) and
+ * reconnected (causing LPM exit). If in LPM initially, sourcing VBUS
+ * consistently causes the charger to report (apparently spurious) overcurrent
+ * failures.
+ *
+ * In short, this is important to making things work correctly but we don't
+ * understand why.
+ */
+static void board_chargers_suspend(struct ap_power_ev_callback *const cb,
+				   const struct ap_power_ev_data data)
+{
+	void (*fn)(int chgnum);
+
+	switch (data.event) {
+	case AP_POWER_SUSPEND:
+		fn = sm5803_enable_low_power_mode;
+		break;
+	case AP_POWER_RESUME:
+		fn = sm5803_disable_low_power_mode;
+		break;
+	default:
+		LOG_WRN("%s: power event %d is not recognized",
+			__func__, data.event);
+		return;
+	}
+
+	fn(CHARGER_PRIMARY);
+	if (board_get_charger_chip_count() > 1)
+		fn(CHARGER_SECONDARY);
+}
+
+static int board_chargers_suspend_init(const struct device *unused)
+{
+	static struct ap_power_ev_callback cb = {
+		.handler = board_chargers_suspend,
+		.events = AP_POWER_SUSPEND | AP_POWER_RESUME,
+	};
+	ap_power_ev_add_callback(&cb);
+	return 0;
+}
+SYS_INIT(board_chargers_suspend_init, APPLICATION, 0);
+
 int board_set_active_charge_port(int port)
 {
 	int is_real_port = (port >= 0 && port < board_get_usb_pd_port_count());