[PATCH v6 02/11] 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       |
+-----------+

Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Gwendal Grignou <gwendal@chromium.org>
---
Changes in v6:
  Comment fixes
Changes in v5:
  Added ack.
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  | 112 ++++++++++++++++--
 1 file changed, 105 insertions(+), 7 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_sensorhub_ring.c b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
index 436f306899252..efe726171bf00 100644
--- a/drivers/platform/chrome/cros_ec_sensorhub_ring.c
+++ b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
@@ -189,6 +189,101 @@ cros_ec_sensor_ring_process_event(struct cros_ec_sensorhub *sensorhub,
 	return true;
 }
 
+/*
+ * cros_ec_sensor_ring_spread_add: Calculate proper timestamps then add to
+ * ringbuffer.
+ *
+ * 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_sensor_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
  *
@@ -300,10 +395,10 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
 		goto ring_handler_end;
 
 	/*
-	 * Check if current_timestamp is ahead of the last sample.
-	 * Normally, the EC appends a timestamp after the last sample, but if
-	 * the AP is slow to respond to the IRQ, the EC may have added new
-	 * samples. Use the FIFO info timestamp as last timestamp then.
+	 * Check if current_timestamp is ahead of the last sample. Normally,
+	 * the EC appends a timestamp after the last sample, but if the AP
+	 * is slow to respond to the IRQ, the EC may have added new samples.
+	 * Use the FIFO info timestamp as last timestamp then.
 	 */
 	if ((last_out - 1)->timestamp == current_timestamp)
 		current_timestamp = fifo_timestamp;
@@ -323,9 +418,12 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
 		}
 	}
 
-	/* Push the event into the FIFO. */
-	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_sensor_ring_spread_add(sensorhub, sensor_mask,
+				       current_timestamp, last_out);
 
 ring_handler_end:
 	sensorhub->fifo_timestamp[CROS_EC_SENSOR_LAST_TS] = current_timestamp;
-- 
2.25.1.696.g5e7596f4ac-goog