[PATCH v2] platform/chrome: sensorhub: Fix dropped timestamp events and log spam

[Tzung-Bi Shih <tzungbi@kernel.org>]

Commit 833740a2333c ("platform/chrome: sensorhub: Bound the EC-reported
sensor number") evaluated the `sensor_num` against the bounds limit even
for timestamp events.  A timestamp event typically has a `sensor_num` of
0xff [1], causing the driver to flag it as invalid and skip to the next
event.

As a result, we'd see a flooding of "Invalid sensor number 255 from EC"
warning logs and these timestamp events were being dropped.

Move the bounds-check into cros_ec_sensor_ring_process_event() and
evaluate it only after standalone timestamp events have already been
processed and returned early.

[1] https://crrev.com/219ca6ef82ba266da788b673ee4ad50bd3ea1285/common/motion_sense_fifo.c#427

Fixes: 833740a2333c ("platform/chrome: sensorhub: Bound the EC-reported sensor number")
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
---
Bryam: sorry for reverting the decision (moving back the check to
cros_ec_sensor_ring_process_event()).  I realized we need to prevent
dropping timestamp events and flooding the logs.
---
v2:
- Move the check to cros_ec_sensor_ring_process_event().
- Return earlier for standalone timestamp events.

v1: https://lore.kernel.org/all/20260714065202.3248017-1-tzungbi@kernel.org
---
 .../platform/chrome/cros_ec_sensorhub_ring.c  | 27 ++++++++++---------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_sensorhub_ring.c b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
index 92941924c347..d92b60213720 100644
--- a/drivers/platform/chrome/cros_ec_sensorhub_ring.c
+++ b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
@@ -475,6 +475,21 @@ cros_ec_sensor_ring_process_event(struct cros_ec_sensorhub *sensorhub,
 						  fifo_timestamp,
 						  *current_timestamp,
 						  now);
+
+		/*
+		 * A standalone timestamp event typically has a sensor_num of
+		 * 0xff.  Return early here to prevent it from hitting the
+		 * bounds check below and spamming the logs.
+		 */
+		return false;
+	}
+
+	/* Skip event if sensor_num from EC is out of bounds. */
+	if (in->sensor_num >= sensorhub->sensor_num) {
+		dev_warn_ratelimited(sensorhub->dev,
+				     "Invalid sensor number %u from EC\n",
+				     in->sensor_num);
+		return false;
 	}
 
 	if (in->flags & MOTIONSENSE_SENSOR_FLAG_ODR) {
@@ -502,10 +517,6 @@ cros_ec_sensor_ring_process_event(struct cros_ec_sensorhub *sensorhub,
 		return true;
 	}
 
-	if (in->flags & MOTIONSENSE_SENSOR_FLAG_TIMESTAMP)
-		/* If we just have a timestamp, skip this entry. */
-		return false;
-
 	/* Regular sample */
 	out->sensor_id = in->sensor_num;
 	trace_cros_ec_sensorhub_data(in->sensor_num,
@@ -897,14 +908,6 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
 
 		for (in = sensorhub->resp->fifo_read.data, j = 0;
 		     j < number_data; j++, in++) {
-			/* Skip event if sensor_num from EC is out of bounds. */
-			if (in->sensor_num >= sensorhub->sensor_num) {
-				dev_warn_ratelimited(sensorhub->dev,
-						     "Invalid sensor number %u from EC\n",
-						     in->sensor_num);
-				continue;
-			}
-
 			if (cros_ec_sensor_ring_process_event(
 						sensorhub, fifo_info,
 						fifo_timestamp,
-- 
2.55.0.229.g6434b31f56-goog