mb/google/{auron,slippy}/ec: clear pending events on S3 wakeup

Commit 6ae8b50 [chromeec: Depend on events_copy_b to identify wake source]
partially broke resume from suspend on Auron and Slippy variants when
multiple events exist in the EC event queue. In the case of the device
suspending manually and then subsequently having the lid closed, the device
will be stuck in a resume/suspend/resume loop until the device is forcibly
powered down.

Mitigate this by clearing any pending EC events on S3 wakeup.

Test: build/boot several Auron/Slippy variants, test suspend/resume functional
with both single and multiple events in EC event queue.

Change-Id: I7ec9ec575d41c5b7522c4e13fc32b0b7c77d20d9
Signed-off-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38984
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

1 files changed, 8 insertions, 1 deletions

diff --git a/src/mainboard/google/slippy/ec.c b/src/mainboard/google/slippy/ec.c
index f8ab6b81d5..e296575a92 100644
--- a/src/mainboard/google/slippy/ec.c
+++ b/src/mainboard/google/slippy/ec.c
@@ -28,10 +28,17 @@ void mainboard_ec_init(void)
 		.s5_wake_events = MAINBOARD_EC_S5_WAKE_EVENTS,
 	};
 
+	int s3_wakeup = acpi_is_wakeup_s3();
+
 	printk(BIOS_DEBUG, "mainboard_ec_init\n");
 	post_code(0xf0);
 
-	google_chromeec_events_init(&info, acpi_is_wakeup_s3());
+	google_chromeec_events_init(&info, s3_wakeup);
+	if (s3_wakeup) {
+		/* Clear pending events. */
+		while (google_chromeec_get_event() != 0)
+			;
+	}
 
 	post_code(0xf1);
 }