[PATCH v4 10/17] platform: chrome: sensorhub: Add code to spread timestmap

[Gwendal Grignou <gwendal@chromium.org>]

EC FIFO can send sensor events in batch. Spread them based on
previous (TSa) and currnet timestamp (TSb)

  EC FIFO                             iio events
+-----------+
| TSa       |
+-----------+             +---------------------------------------+
| event 1   |             | event 1 | TSb - (TSb - TSa)/n * (n-1) |
+-----------+             +---------------------------------------+
| event 2   |             | event 2 | TSb - (TSb - TSa)/n * (n-2) |
+-----------+             +---------------------------------------+
|  ...      |  ------>    |  ....   |                             |
+-----------+             +---------------------------------------+
| event n-1 |             | event 2 | TSb - (TSb - TSa)/n         |
+-----------+             +---------------------------------------+
| event n   |             | event 2 | TSb                         |
+-----------+             +---------------------------------------+
| TSb       |
+-----------+

Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
---
Changes in v4:
- Check patch with --strict option
    Alignement
No changes in v3.
Changes in v2:
- Use CROS_EC_SENSOR_LAST_TS instead of LAST_TS to avoid name colisions.

 .../platform/chrome/cros_ec_sensorhub_ring.c  | 98 ++++++++++++++++++-
 1 file changed, 95 insertions(+), 3 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_sensorhub_ring.c b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
index f091f2a4ccfe..b22a71406742 100644
--- a/drivers/platform/chrome/cros_ec_sensorhub_ring.c
+++ b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
@@ -187,6 +187,96 @@ static bool cros_ec_ring_process_event(struct cros_ec_sensorhub *sensorhub,
 	return true;
 }
 
+/*
+ * cros_ec_ring_spread_add: Calculate proper timestamps then
+ * add to ringbuffer (legacy).
+ *
+ * If there is a sample with a proper timestamp
+ *                        timestamp | count
+ * older_unprocess_out --> TS1      | 1
+ *                         TS1      | 2
+ * out -->                 TS1      | 3
+ * next_out -->            TS2      |
+ * We spread time for the samples [older_unprocess_out .. out]
+ * between TS1 and TS2: [TS1+1/4, TS1+2/4, TS1+3/4, TS2].
+ *
+ * If we reach the end of the samples, we compare with the
+ * current timestamp:
+ *
+ * older_unprocess_out --> TS1      | 1
+ *                         TS1      | 2
+ * out -->                 TS1      | 3
+ * We know have [TS1+1/3, TS1+2/3, current timestamp]
+ */
+static void cros_ec_ring_spread_add(struct cros_ec_sensorhub *sensorhub,
+				unsigned long sensor_mask,
+				s64 current_timestamp,
+				struct cros_ec_sensors_ring_sample *last_out)
+{
+	struct cros_ec_sensors_ring_sample *out;
+	int i;
+
+	for_each_set_bit(i, &sensor_mask, BITS_PER_LONG) {
+		s64 older_timestamp;
+		s64 timestamp;
+		struct cros_ec_sensors_ring_sample *older_unprocess_out =
+			sensorhub->ring;
+		struct cros_ec_sensors_ring_sample *next_out;
+		int count = 1;
+
+		for (out = sensorhub->ring; out < last_out; out = next_out) {
+			s64 time_period;
+
+			next_out = out + 1;
+			if (out->sensor_id != i)
+				continue;
+
+			/* Timestamp to start with */
+			older_timestamp = out->timestamp;
+
+			/* find next sample */
+			while (next_out < last_out && next_out->sensor_id != i)
+				next_out++;
+
+			if (next_out >= last_out) {
+				timestamp = current_timestamp;
+			} else {
+				timestamp = next_out->timestamp;
+				if (timestamp == older_timestamp) {
+					count++;
+					continue;
+				}
+			}
+
+			/*
+			 * The next sample has a new timestamp,
+			 * spread the unprocessed samples.
+			 */
+			if (next_out < last_out)
+				count++;
+			time_period = div_s64(timestamp - older_timestamp,
+					      count);
+
+			for (; older_unprocess_out <= out;
+					older_unprocess_out++) {
+				if (older_unprocess_out->sensor_id != i)
+					continue;
+				older_timestamp += time_period;
+				older_unprocess_out->timestamp =
+					older_timestamp;
+			}
+			count = 1;
+			/* The next_out sample has a valid timestamp, skip. */
+			next_out++;
+			older_unprocess_out = next_out;
+		}
+	}
+
+	/* push the event into the kfifo */
+	for (out = sensorhub->ring; out < last_out; out++)
+		cros_sensorhub_send_sample(sensorhub, out);
+}
+
 /*
  * cros_ec_sensorhub_ring_handler - the trigger handler function
  *
@@ -322,9 +412,11 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
 		}
 	}
 
-	/* push the event into the kfifo */
-	for (out = sensorhub->ring; out < last_out; out++)
-		cros_sensorhub_send_sample(sensorhub, out);
+	/*
+	 * Spread samples in case of batching, then add them to the ringbuffer.
+	 */
+	cros_ec_ring_spread_add(sensorhub, sensor_mask,
+			current_timestamp, last_out);
 
 ring_handler_end:
 	sensorhub->fifo_timestamp[CROS_EC_SENSOR_LAST_TS] = current_timestamp;
-- 
2.24.0.rc1.363.gb1bccd3e3d-goog