platform/chrome: cros_ec_proto: ignore unnecessary wakeups on old ECs

ECs that don't implement EC_CMD_HOST_EVENT_GET_WAKE_MASK should still
have some reasonable default mask -- otherwise, they'll treat a variety
of EC signals as spurious wakeups. Battery and AC events can be
especially common, for devices that have been sitting at full charge
plugged into AC for a long time, as they may cycle their charging off
and on, or their battery may start reporting failures as it ages.

Treating these as wakeups does not serve a useful purpose, and is
instead often counterproductive. And indeed, later ECs (that implement
the mask) don't include these events in their wake-mask.

Note that this patch doesn't do anything without the subsequent patch
("platform/chrome: cros_ec_proto: check for missing
EC_CMD_HOST_EVENT_GET_WAKE_MASK"), because
cros_ec_get_host_event_wake_mask() currently does not return an error if
EC_CMD_HOST_EVENT_GET_WAKE_MASK is not implemented.

Some additional notes:
While the EC typically knows not to wake the CPU for these unimportant
events once the CPU reaches a sleep state, it doesn't really have a way
to know that the CPU is "almost" asleep, unless it has support for
EC_CMD_HOST_SLEEP_EVENT. Alas, these older ECs do not support that
command either, so this solution is not 100% complete.
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

drivers/platform/chrome/cros_ec_proto.c

@@ -469,14 +469,26 @@ int cros_ec_query_all(struct cros_ec_device *ec_dev)
 						    &ver_mask);
 	ec_dev->host_sleep_v1 = (ret >= 0 && (ver_mask & EC_VER_MASK(1)));
 
-	/*
-	 * Get host event wake mask, assume all events are wake events
-	 * if unavailable.
-	 */
+	/* Get host event wake mask. */
 	ret = cros_ec_get_host_event_wake_mask(ec_dev, proto_msg,
 					       &ec_dev->host_event_wake_mask);
-	if (ret < 0)
-		ec_dev->host_event_wake_mask = U32_MAX;
+	if (ret < 0) {
+		/*
+		 * If the EC doesn't support EC_CMD_HOST_EVENT_GET_WAKE_MASK,
+		 * use a reasonable default. Note that we ignore various
+		 * battery, AC status, and power-state events, because (a)
+		 * those can be quite common (e.g., when sitting at full
+		 * charge, on AC) and (b) these are not actionable wake events;
+		 * if anything, we'd like to continue suspending (to save
+		 * power), not wake up.
+		 */
+		ec_dev->host_event_wake_mask = U32_MAX &
+			~(BIT(EC_HOST_EVENT_AC_DISCONNECTED) |
+			  BIT(EC_HOST_EVENT_BATTERY_LOW) |
+			  BIT(EC_HOST_EVENT_BATTERY_CRITICAL) |
+			  BIT(EC_HOST_EVENT_PD_MCU) |
+			  BIT(EC_HOST_EVENT_BATTERY_STATUS));
+	}
 
 	ret = 0;