Re: [PATCH 08/13] platform: chrome: sensorhub: Add code to spread timestmap

[Jonathan Cameron <jic23@kernel.org>]

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;