[PATCH] drivers: iio: cros_ec_sensors: Flush changing the FIFO timeout

[Gwendal Grignou <gwendal@chromium.org>]

From: Gwendal Grignou <gwendal@chromium.org>

fifo_timeout is used by the EC firmware only when a new sample is
available.
When the timeout changes, espcially when the new timeout is shorter than
the current one, we need to send the samples waiting in the FIFO.

Change-Id: Iec40367472bd301123c22e38d0ad8aca4ed41379
---
 .../cros_ec_sensors/cros_ec_sensors_core.c    | 51 ++++++++++++-------
 1 file changed, 33 insertions(+), 18 deletions(-)

diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
index bd8483866d046..339faee6ab44b 100644
--- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
+++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
@@ -105,22 +105,6 @@ static void get_default_min_max_freq(enum motionsensor_type type,
 	}
 }
 
-static int cros_ec_sensor_set_ec_rate(struct cros_ec_sensors_core_state *st,
-				      int rate)
-{
-	int ret;
-
-	if (rate > U16_MAX)
-		rate = U16_MAX;
-
-	mutex_lock(&st->cmd_lock);
-	st->param.cmd = MOTIONSENSE_CMD_EC_RATE;
-	st->param.ec_rate.data = rate;
-	ret = cros_ec_motion_send_host_cmd(st, 0);
-	mutex_unlock(&st->cmd_lock);
-	return ret;
-}
-
 static ssize_t cros_ec_sensor_set_report_latency(struct device *dev,
 						 struct device_attribute *attr,
 						 const char *buf, size_t len)
@@ -136,7 +120,25 @@ static ssize_t cros_ec_sensor_set_report_latency(struct device *dev,
 
 	/* EC rate is in ms. */
 	latency = integer * 1000 + fract / 1000;
-	ret = cros_ec_sensor_set_ec_rate(st, latency);
+
+	mutex_lock(&st->cmd_lock);
+	st->param.cmd = MOTIONSENSE_CMD_EC_RATE;
+	st->param.ec_rate.data = min(U16_MAX, latency);
+	ret = cros_ec_motion_send_host_cmd(st, 0);
+	mutex_unlock(&st->cmd_lock);
+	if (ret < 0)
+		return ret;
+
+	/*
+	 * Flush samples currently in the FIFO, expecially when the new latency
+	 * is shorter than the old one: new timeout value is only considered when
+	 * there is a new sample available. It can take a while for a slow
+	 * sensor.
+	 */
+	mutex_lock(&st->cmd_lock);
+	st->param.cmd = MOTIONSENSE_CMD_FIFO_FLUSH;
+	ret = cros_ec_motion_send_host_cmd(st, 0);
+	mutex_unlock(&st->cmd_lock);
 	if (ret < 0)
 		return ret;
 
@@ -154,7 +156,6 @@ static ssize_t cros_ec_sensor_get_report_latency(struct device *dev,
 	mutex_lock(&st->cmd_lock);
 	st->param.cmd = MOTIONSENSE_CMD_EC_RATE;
 	st->param.ec_rate.data = EC_MOTION_SENSE_NO_VALUE;
-
 	ret = cros_ec_motion_send_host_cmd(st, 0);
 	latency = st->resp->ec_rate.ret;
 	mutex_unlock(&st->cmd_lock);
@@ -769,6 +770,8 @@ EXPORT_SYMBOL_GPL(cros_ec_sensors_capture);
  * @mask:	specifies which values to be requested
  *
  * Return:	the type of value returned by the device
+ *
+ * cmd_lock mutex held.
  */
 int cros_ec_sensors_core_read(struct cros_ec_sensors_core_state *st,
 			  struct iio_chan_spec const *chan,
@@ -841,6 +844,8 @@ EXPORT_SYMBOL_GPL(cros_ec_sensors_core_read_avail);
  * @mask:	specifies which values to write
  *
  * Return:	the type of value returned by the device
+ *
+ * cmd_lock mutex held.
  */
 int cros_ec_sensors_core_write(struct cros_ec_sensors_core_state *st,
 			       struct iio_chan_spec const *chan,
@@ -858,6 +863,16 @@ int cros_ec_sensors_core_write(struct cros_ec_sensors_core_state *st,
 		st->param.sensor_odr.roundup = 1;
 
 		ret = cros_ec_motion_send_host_cmd(st, 0);
+
+		/* Flush the FIFO in case we are stopping a sensor.
+		 * If the FIFO has just been emptied, pending samples will be
+		 * stuck until new samples are available. It will not happen
+		 * when all the sensors are stopped.
+		 */
+		if (frequency == 0) {
+			st->param.cmd = MOTIONSENSE_CMD_FIFO_FLUSH;
+			cros_ec_motion_send_host_cmd(st, 0);
+		}
 		break;
 	default:
 		ret = -EINVAL;
-- 
2.49.0.472.ge94155a9ec-goog