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SubjectRe: [PATCH 08/13] platform: chrome: sensorhub: Add code to spread timestmap
On Sun, 22 Sep 2019 10:50:16 -0700
Gwendal Grignou <gwendal@chromium.org> wrote:

> 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>
Looks fine to me and the docs are nice :)
Timestamps for batches are always a pita.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
> .../platform/chrome/cros_ec_sensorhub_ring.c | 99 ++++++++++++++++++-
> 1 file changed, 96 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/platform/chrome/cros_ec_sensorhub_ring.c b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
> index 8cd533d5542e..48327e80a5a3 100644
> --- a/drivers/platform/chrome/cros_ec_sensorhub_ring.c
> +++ b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
> @@ -160,6 +160,97 @@ static bool cros_ec_ring_process_event(
> 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
> *
> @@ -280,9 +371,11 @@ 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[LAST_TS] = current_timestamp;

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