platform/chrome: cros_ec_sensorhub: Add median filter

Events are timestamped in EC time space, their timestamps need to be
converted in host time space.

The assumption is the time delta between when the interrupt is sent
by the EC and when it is receive by the host is a [small] constant.
This is not always true, even with hard-wired interrupt. To mitigate
worst offenders, add a median filter to weed out bigger than expected
delays.

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>

1 files changed, 89 insertions, 4 deletions

diff --git a/include/linux/platform_data/cros_ec_sensorhub.h b/include/linux/platform_data/cros_ec_sensorhub.h
index b0950814f820..c588be843f61 100644
--- a/include/linux/platform_data/cros_ec_sensorhub.h
+++ b/include/linux/platform_data/cros_ec_sensorhub.h
@@ -54,7 +54,64 @@ struct cros_ec_sensors_ring_sample {
 	s64 timestamp;
 } __packed;
 
+/* State used for cros_ec_ring_fix_overflow */
+struct cros_ec_sensors_ec_overflow_state {
+	s64 offset;
+	s64 last;
+};
+
+/* Length of the filter, how long to remember entries for */
+#define CROS_EC_SENSORHUB_TS_HISTORY_SIZE 64
+
 /**
+ * struct cros_ec_sensors_ts_filter_state - Timestamp filetr state.
+ *
+ * @x_offset: x is EC interrupt time. x_offset its last value.
+ * @y_offset: y is the difference between AP and EC time, y_offset its last
+ *            value.
+ * @x_history: The past history of x, relative to x_offset.
+ * @y_history: The past history of y, relative to y_offset.
+ * @m_history: rate between y and x.
+ * @history_len: Amount of valid historic data in the arrays.
+ * @temp_buf: Temporary buffer used when updating the filter.
+ * @median_m: median value of m_history
+ * @median_error: final error to apply to AP interrupt timestamp to get the
+ *                "true timestamp" the event occurred.
+ */
+struct cros_ec_sensors_ts_filter_state {
+	s64 x_offset, y_offset;
+	s64 x_history[CROS_EC_SENSORHUB_TS_HISTORY_SIZE];
+	s64 y_history[CROS_EC_SENSORHUB_TS_HISTORY_SIZE];
+	s64 m_history[CROS_EC_SENSORHUB_TS_HISTORY_SIZE];
+	int history_len;
+
+	s64 temp_buf[CROS_EC_SENSORHUB_TS_HISTORY_SIZE];
+
+	s64 median_m;
+	s64 median_error;
+};
+
+/* struct cros_ec_sensors_ts_batch_state - State of batch of a single sensor.
+ *
+ * Use to store information to batch data using median fileter information.
+ *
+ * @penul_ts: last but one batch timestamp (penultimate timestamp).
+ *	      Used for timestamp spreading calculations
+ *	      when a batch shows up.
+ * @penul_len: last but one batch length.
+ * @last_ts: Last batch timestam.
+ * @last_len: Last batch length.
+ * @newest_sensor_event: Last sensor timestamp.
+ */
+struct cros_ec_sensors_ts_batch_state {
+	s64 penul_ts;
+	int penul_len;
+	s64 last_ts;
+	int last_len;
+	s64 newest_sensor_event;
+};
+
+/*
  * struct cros_ec_sensorhub - Sensor Hub device data.
  *
  * @dev: Device object, mostly used for logging.
@@ -66,10 +123,26 @@ struct cros_ec_sensors_ring_sample {
  * @cmd_lock : Lock for sending msg.
  * @notifier: Notifier to kick the FIFO interrupt.
  * @ring: Preprocessed ring to store events.
- * @fifo_timestamp: array for event timestamp and spreading.
- * @fifo_info: copy of FIFO information coming from the EC.
- * @fifo_size: size of the ring.
- * @push_data: array of callback to send datums to iio sensor object.
+ * @fifo_timestamp: Array for event timestamp and spreading.
+ * @fifo_info: Copy of FIFO information coming from the EC.
+ * @fifo_size: Size of the ring.
+ * @batch_state: Per sensor information of the last batches received.
+ * @overflow_a: For handling timestamp overflow for a time (sensor events)
+ * @overflow_b: For handling timestamp overflow for b time (ec interrupts)
+ * @filter: Medium fileter structure.
+ * @tight_timestamps: Set to truen when EC support tight timestamping:
+ *		      The timestamps reported from the EC have low jitter.
+ *		      Timestamps also come before every sample. Set either
+ *		      by feature bits coming from the EC or userspace.
+ * @future_timestamp_count: Statistics used to compute shaved time.
+ *			    This occurs when timestamp interpolation from EC
+ *			    time to AP time accidentally puts timestamps in
+ *			    the future. These timestamps are clamped to
+ *			    `now` and these count/total_ns maintain the
+ *			    statistics for how much time was removed in a
+ *			    given period.
+ * @future_timestamp_total_ns: Total amount of time shaved.
+ * @push_data: Array of callback to send datums to iio sensor object.
  */
 struct cros_ec_sensorhub {
 	struct device *dev;
@@ -89,6 +162,18 @@ struct cros_ec_sensorhub {
 	struct ec_response_motion_sense_fifo_info *fifo_info;
 	int fifo_size;
 
+	struct cros_ec_sensors_ts_batch_state *batch_state;
+
+	struct cros_ec_sensors_ec_overflow_state overflow_a;
+	struct cros_ec_sensors_ec_overflow_state overflow_b;
+
+	struct cros_ec_sensors_ts_filter_state filter;
+
+	int tight_timestamps;
+
+	s32 future_timestamp_count;
+	s64 future_timestamp_total_ns;
+
 	struct cros_ec_sensorhub_sensor_push_data *push_data;
 };