Re: [PATCH v4 11/17] platform: chrome: sensorhub: Add median filter

Jonathan Cameron
2019-11-10T13:07:29Z

On Tue, 5 Nov 2019 14:26:46 -0800
Gwendal Grignou <gwendal@chromium.org> wrote:

> 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>
A few minor things inline seeing as you will be respinning.
Again, I've not checked the maths as don't have that much time available!

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

> ---
> Changes in v4:
> - Keep defining cros_ec_sensorhub in kernel-doc format
> - Check patch with --strict option
> Use BIT()
> Add spaces around '-'
> Alignement
> Changes in v3:
> - Fix doxygen code.
> Changes in v2:
> - Move some #define in .c to prevent name collisions.
> - Add proper doxygen comments.
> - Use /* instead of //
>
> .../platform/chrome/cros_ec_sensorhub_ring.c | 505 +++++++++++++++++-
> .../linux/platform_data/cros_ec_sensorhub.h | 75 +++
> 2 files changed, 562 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/platform/chrome/cros_ec_sensorhub_ring.c b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
> index b22a71406742..8960081caeba 100644
> --- a/drivers/platform/chrome/cros_ec_sensorhub_ring.c
> +++ b/drivers/platform/chrome/cros_ec_sensorhub_ring.c
> @@ -18,6 +18,21 @@
> #include <linux/sort.h>
> #include <linux/slab.h>
>
> +/* Precision of fixed point for the m values from the filter */
> +#define M_PRECISION BIT(23)
> +
> +/* Only activate the filter once we have at least this many elements. */
> +#define TS_HISTORY_THRESHOLD 8
> +
> +/*
> + * If we don't have any history entries for this long, empty the filter to
> + * make sure there are no big discontinuities.
> + */
> +#define TS_HISTORY_BORED_US 500000
> +
> +/* To measure by how much the filter is overshooting, if it happens. */
> +#define FUTURE_TS_ANALYTICS_COUNT_MAX 100
> +
> static inline int cros_sensorhub_send_sample(
> struct cros_ec_sensorhub *sensorhub,
> struct cros_ec_sensors_ring_sample *sample)
> @@ -91,9 +106,11 @@ EXPORT_SYMBOL_GPL(cros_ec_sensorhub_unregister_push_data);
> int cros_ec_sensorhub_ring_fifo_enable(struct cros_ec_sensorhub *sensorhub,
> bool on)
> {
> - int ret;
> + int ret, i;
>
> mutex_lock(&sensorhub->cmd_lock);
> + for (i = 0; i < CROS_EC_SENSOR_MAX; i++)
> + sensorhub->last_batch_len[i] = 0;
> sensorhub->params->cmd = MOTIONSENSE_CMD_FIFO_INT_ENABLE;
> sensorhub->params->fifo_int_enable.enable = on;
>
> @@ -110,6 +127,231 @@ int cros_ec_sensorhub_ring_fifo_enable(struct cros_ec_sensorhub *sensorhub,
> return ret;
> }
>
> +static int cros_ec_ring_median_cmp(const void *pv1, const void *pv2)
> +{
> + s64 v1 = *(s64 *)pv1;
> + s64 v2 = *(s64 *)pv2;
> +
> + if (v1 > v2)
> + return 1;
> + else if (v1 < v2)
> + return -1;
> + else
> + return 0;
> +}
> +
> +/*
> + * cros_ec_ring_median: Gets median of an array of numbers
> + *
> + * For now it's implemented using an inefficient > O(n) sort then return
> + * the middle element. A more optimal method would be something like
> + * quickselect, but given that n = 64 we can probably live with it in the
> + * name of clarity.
> + *
> + * Warning: the input array gets modified (sorted)!
> + */
> +static s64 cros_ec_ring_median(s64 *array, size_t length)
> +{
> + sort(array, length, sizeof(s64), cros_ec_ring_median_cmp, NULL);
> + return array[length / 2];
> +}
> +
> +/*
> + * IRQ Timestamp Filtering
> + *
> + * Lower down in cros_ec_ring_process_event(), for each sensor event we have to
> + * calculate it's timestamp in the AP timebase. There are 3 time points:
> + * a - EC timebase, sensor event
> + * b - EC timebase, IRQ
> + * c - AP timebase, IRQ
> + * a' - what we want: sensor even in AP timebase
> + *
> + * While a and b are recorded at accurate times (due to the EC real time
> + * nature); c is pretty untrustworthy, even though it's recorded the
> + * first thing in ec_irq_handler(). There is a very good change we'll get
> + * added lantency due to:
> + * other irqs
> + * ddrfreq
> + * cpuidle
> + *
> + * Normally a' = c - b + a, but if we do that naive math any jitter in c
> + * will get coupled in a', which we don't want. We want a function
> + * a' = cros_ec_ring_ts_filter(a) which will filter out outliers in c.
> + *
> + * Think of a graph of AP time(b) on the y axis vs EC time(c) on the x axis.
> + * The slope of the line won't be exactly 1, there will be some clock drift
> + * between the 2 chips for various reasons (mechanical stress, temperature,
> + * voltage). We need to extrapolate values for a future x, without trusting
> + * recent y values too much.
> + *
> + * We use a median filter for the slope, then another median filter for the
> + * y-intercept to calculate this function:
> + * dx[n] = x[n-1] - x[n]
> + * dy[n] = x[n-1] - x[n]
> + * m[n] = dy[n] / dx[n]
> + * median_m = median(m[n-k:n])
> + * error[i] = y[n-i] - median_m * x[n-i]
> + * median_error = median(error[:k])
> + * predicted_y = median_m * x + median_error
> + *
> + * Implementation differences from above:
> + * - Redefined y to be actually c - b, this gives us a lot more precision
> + * to do the math. (c-b)/b variations are more obvious than c/b variations.
> + * - Since we don't have floating point, any operations involving slope are
> + * done using fixed point math (*M_PRECISION)
> + * - Since x and y grow with time, we keep zeroing the graph (relative to
> + * the last sample), this way math involving *x[n-i] will not overflow
> + * - EC timestamps are kept in us, it improves the slope calculation precision
> + */
> +
> +/**
> + * cros_ec_ring_ts_filter_update - Update filter history.
> + *
> + * @state: Filter information.
> + * @b: IRQ timestamp, EC timebase (us)
> + * @c: IRQ timestamp, AP timebase (ns)
> + *
> + * Given a new IRQ timestamp pair (EC and AP timebases), add it to the filter
> + * history.
> + */
> +static void cros_ec_ring_ts_filter_update(
> + struct cros_ec_sensors_ts_filter_state *state,
> + s64 b, s64 c)
> +{
> + s64 x, y;
> + s64 dx, dy;
> + s64 m; /* stored as *M_PRECISION */
> + s64 *m_history_copy = state->temp_buf;
> + s64 *error = state->temp_buf;
> + int i;
> +
> + /* we trust b the most, that'll be our independent variable */
> + x = b;
> + /* y is the offset between AP and EC times, in ns */
> + y = c - b * 1000;
> +
> + dx = (state->x_history[0] + state->x_offset) - x;
> + if (dx == 0)
> + return; /* we already have this irq in the history */
> + dy = (state->y_history[0] + state->y_offset) - y;
> + m = div64_s64(dy * M_PRECISION, dx);
> +
> + /* Empty filter if we haven't seen any action in a while. */
> + if (-dx > TS_HISTORY_BORED_US)
> + state->history_len = 0;
> +
> + /* Move everything over, also update offset to all absolute coords .*/
> + for (i = state->history_len - 1; i >= 1; i--) {
> + state->x_history[i] = state->x_history[i - 1] + dx;
> + state->y_history[i] = state->y_history[i - 1] + dy;
> +
> + state->m_history[i] = state->m_history[i - 1];
> + /*
> + * Also use the same loop to copy m_history for future
> + * median extraction.
> + */
> + m_history_copy[i] = state->m_history[i - 1];
> + }
> +
> + /* Store the x and y, but remember offset is actually last sample. */
> + state->x_offset = x;
> + state->y_offset = y;
> + state->x_history[0] = 0;
> + state->y_history[0] = 0;
> +
> + state->m_history[0] = m;
> + m_history_copy[0] = m;
> +
> + if (state->history_len < CROS_EC_SENSORHUB_TS_HISTORY_SIZE)
> + state->history_len++;
> +
> + /* Precalculate things for the filter. */
> + if (state->history_len > TS_HISTORY_THRESHOLD) {
> + state->median_m =
> + cros_ec_ring_median(m_history_copy, state->history_len - 1);
> +
> + /*
> + * Calculate y-intercepts as if m_median is the slope and
> + * points in the history are on the line. median_error will
> + * still be in the offset coordinate system.
> + */
> + for (i = 0; i < state->history_len; i++)
> + error[i] = state->y_history[i] -
> + div_s64(state->median_m * state->x_history[i],
> + M_PRECISION);
> + state->median_error =
> + cros_ec_ring_median(error, state->history_len);
> + } else {
> + state->median_m = 0;
> + state->median_error = 0;
> + }
> +}
> +
> +/**
> + * cros_ec_ring_ts_filter - Translate EC timebase timestamp to AP timebase
> + *
> + * @state: filter information.
> + * @x: any ec timestamp (us):
> + *
> + * cros_ec_ring_ts_filter(a) => a' event timestamp, AP timebase
> + * cros_ec_ring_ts_filter(b) => calculated timestamp when the EC IRQ
> + * should have happened on the AP, with low jitter
> + *
> + * Note: The filter will only activate once state->history_len goes
> + * over TS_HISTORY_THRESHOLD. Otherwise it'll just do the naive c - b + a
> + * transform.
> + *
> + * How to derive the formula, starting from:
> + * f(x) = median_m * x + median_error
> + * That's the calculated AP - EC offset (at the x point in time)
> + * Undo the coordinate system transform:
> + * f(x) = median_m * (x - x_offset) + median_error + y_offset
> + * Remember to undo the "y = c - b * 1000" modification:
> + * f(x) = median_m * (x - x_offset) + median_error + y_offset + x * 1000
> + *
> + * Return: timestamp in AP timebase (ns)
> + */
> +static s64 cros_ec_ring_ts_filter(struct cros_ec_sensors_ts_filter_state *state,
> + s64 x)
> +{
> + return div_s64(state->median_m * (x - state->x_offset), M_PRECISION)
> + + state->median_error + state->y_offset + x * 1000;
> +}
> +
> +/*
> + * Since a and b were originally 32 bit values from the EC,
> + * they overflow relatively often, casting is not enough, so we need to
> + * add an offset.
> + */
> +static void cros_ec_ring_fix_overflow(s64 *ts,
> + const s64 overflow_period,
> + struct cros_ec_sensors_ec_overflow_state *state)
> +{
> + s64 adjust;
> +
> + *ts += state->offset;
> + if (abs(state->last - *ts) > (overflow_period / 2)) {
> + adjust = state->last > *ts ? overflow_period : -overflow_period;
> + state->offset += adjust;
> + *ts += adjust;
> + }
> + state->last = *ts;
> +}
> +
> +static void cros_ec_ring_check_for_past_timestamp(
> + struct cros_ec_sensorhub *sensorhub,
> + struct cros_ec_sensors_ring_sample *sample)
> +{
> + const u8 sensor_id = sample->sensor_id;
> +
> + /* If this event is earlier than one we saw before... */
> + if (sensorhub->newest_sensor_event[sensor_id] > sample->timestamp)
> + /* mark it for spreading. */
> + sample->timestamp = sensorhub->last_batch_timestamp[sensor_id];
> + else
> + sensorhub->newest_sensor_event[sensor_id] = sample->timestamp;
> +}
> +
> /**
> * cros_ec_ring_process_event - process one EC FIFO event
> *
> @@ -141,32 +383,54 @@ static bool cros_ec_ring_process_event(struct cros_ec_sensorhub *sensorhub,
> s64 a = in->timestamp;
> s64 b = fifo_info->info.timestamp;
> s64 c = fifo_timestamp;
> - s64 new_timestamp;
>
> - /*
> - * disable filtering since we might add more jitter
> - * if b is in a random point in time
> - */
> - new_timestamp = c - b * 1000 + a * 1000;
> + cros_ec_ring_fix_overflow(&a, 1LL << 32,
> + &sensorhub->overflow_a);
> + cros_ec_ring_fix_overflow(&b, 1LL << 32,
> + &sensorhub->overflow_b);
> +
> + if (sensorhub->tight_timestamps) {
> + cros_ec_ring_ts_filter_update(&sensorhub->filter, b, c);
> + *current_timestamp =
> + cros_ec_ring_ts_filter(&sensorhub->filter, a);
> + } else {
> + s64 new_timestamp;
> + /*
> + * disable filtering since we might add more jitter
> + * if b is in a random point in time
> + */
> + new_timestamp = c - b * 1000 + a * 1000;
> + /*
> + * The timestamp can be stale if we had to use the fifo
> + * info timestamp.
> + */
> + if (new_timestamp - *current_timestamp > 0)
> + *current_timestamp = new_timestamp;
> + }
> + }
>
> + if (in->flags & MOTIONSENSE_SENSOR_FLAG_ODR) {
> + sensorhub->last_batch_len[in->sensor_num] =
> + sensorhub->penultimate_batch_len[in->sensor_num] = 0;
> /*
> - * The timestamp can be stale if we had to use the fifo
> - * info timestamp.
> + * ODR change is only useful for the sensor_ring, it does not
> + * convey information to clients.
> */
> - if (new_timestamp - *current_timestamp > 0)
> - *current_timestamp = new_timestamp;
> + return false;
> }
>
> if (in->flags & MOTIONSENSE_SENSOR_FLAG_FLUSH) {
> out->sensor_id = in->sensor_num;
> out->timestamp = *current_timestamp;
> out->flag = in->flags;
> + sensorhub->last_batch_len[out->sensor_id] = 0;
> /*
> * No other payload information provided with
> * flush ack.
> */
> return true;
> }
> +

Unrelated change. Would rather not see those in a series doing interesting
things like this.

> if (in->flags & MOTIONSENSE_SENSOR_FLAG_TIMESTAMP)
> /* If we just have a timestamp, skip this entry. */
> return false;
> @@ -174,7 +438,22 @@ static bool cros_ec_ring_process_event(struct cros_ec_sensorhub *sensorhub,
> /* Regular sample */
> out->sensor_id = in->sensor_num;
> if (*current_timestamp - now > 0) {
> - /* If the timestamp is in the future. */
> + /*
> + * This fix is needed to overcome the timestamp filter putting
> + * events in the future.
> + */
> + sensorhub->future_timestamp_total_ns +=
> + *current_timestamp - now;
> + if (++sensorhub->future_timestamp_count ==
> + FUTURE_TS_ANALYTICS_COUNT_MAX) {
> + s64 avg = div_s64(sensorhub->future_timestamp_total_ns,
> + sensorhub->future_timestamp_count);
> + dev_warn(sensorhub->dev,
> + "100 timestamps in the future, %lldns shaved on average\n",
> + avg);

I'll assume this actually happens from time to time given the effort you are putting
in to handle it. If so do we want near uncontrolled spamming of the log?

> + sensorhub->future_timestamp_count = 0;
> + sensorhub->future_timestamp_total_ns = 0;
> + }
> out->timestamp = now;
> } else {
> out->timestamp = *current_timestamp;
> @@ -184,13 +463,194 @@ static bool cros_ec_ring_process_event(struct cros_ec_sensorhub *sensorhub,
> for (axis = 0; axis < 3; axis++)
> out->vector[axis] = in->data[axis];
>
> + if (sensorhub->tight_timestamps)
> + cros_ec_ring_check_for_past_timestamp(sensorhub, out);
> return true;
> }
>
> /*
> - * cros_ec_ring_spread_add: Calculate proper timestamps then
> + * cros_ec_ring_spread_add: Calculate proper timestamps then add to ringbuffer.
> + *
> + * Note: This is the new spreading code, assumes every sample's timestamp
> + * preceeds the sample. Run if tight_timestamps == true.
> + *
> + * Sometimes the EC receives only one interrupt (hence timestamp) for
> + * a batch of samples. Only the first sample will have the correct
> + * timestamp. So we must interpolate the other samples.
> + * We use the previous batch timestamp and our current batch timestamp
> + * as a way to calculate period, then spread the samples evenly.
> + *
> + * s0 int, 0ms
> + * s1 int, 10ms
> + * s2 int, 20ms
> + * 30ms point goes by, no interrupt, previous one is still asserted
> + * downloading s2 and s3
> + * s3 sample, 20ms (incorrect timestamp)
> + * s4 int, 40ms
> + *
> + * The batches are [(s0), (s1), (s2, s3), (s4)]. Since the 3rd batch
> + * has 2 samples in them, we adjust the timestamp of s3.
> + * s2 - s1 = 10ms, so s3 must be s2 + 10ms => 20ms. If s1 would have
> + * been part of a bigger batch things would have gotten a little
> + * more complicated.
> + *
> + * Note: we also assume another sensor sample doesn't break up a batch
> + * in 2 or more partitions. Example, there can't ever be a sync sensor
> + * in between S2 and S3. This simplifies the following code.
> + */
> +static void cros_ec_ring_spread_add(
> + struct cros_ec_sensorhub *sensorhub,
> + unsigned long sensor_mask,
> + struct cros_ec_sensors_ring_sample *last_out)
> +{
> + struct cros_ec_sensors_ring_sample *batch_start, *next_batch_start;
> + int id;
> +
> + for_each_set_bit(id, &sensor_mask, BITS_PER_LONG) {
> + for (batch_start = sensorhub->ring; batch_start < last_out;
> + batch_start = next_batch_start) {
> + /*
> + * For each batch (where all samples have the same
> + * timestamp).
> + */
> + int batch_len, sample_idx;
> + struct cros_ec_sensors_ring_sample *batch_end =
> + batch_start;
> + struct cros_ec_sensors_ring_sample *s;
> + s64 batch_timestamp = batch_start->timestamp;
> + s64 sample_period;
> +
> + /*
> + * Skip over batches that start with the sensor types
> + * we're not looking at right now.
> + */
> + if (batch_start->sensor_id != id) {
> + next_batch_start = batch_start + 1;
> + continue;
> + }
> +
> + /*
> + * Do not start a batch
> + * from a flush, as it happens asynchronously to the
> + * regular flow of events.
> + */
> + if (batch_start->flag & MOTIONSENSE_SENSOR_FLAG_FLUSH) {
> + cros_sensorhub_send_sample(sensorhub,
> + batch_start);
> + next_batch_start = batch_start + 1;
> + continue;
> + }
> +
> + if (batch_start->timestamp <=
> + sensorhub->last_batch_timestamp[id]) {
> + batch_timestamp =
> + sensorhub->last_batch_timestamp[id];
> + batch_len = sensorhub->last_batch_len[id];
> +
> + sample_idx = batch_len;
> +
> + sensorhub->last_batch_timestamp[id] =
> + sensorhub->penultimate_batch_timestamp[id];
> + sensorhub->last_batch_len[id] =
> + sensorhub->penultimate_batch_len[id];
> + } else {
> + /*
> + * Push first sample in the batch to the,
> + * kifo, it's guaranteed to be correct, the
> + * rest will follow later on.
> + */
> + sample_idx = 1;
> + batch_len = 1;
> + cros_sensorhub_send_sample(sensorhub,
> + batch_start);
> + batch_start++;
> + }
> +
> + /* Find all samples have the same timestamp. */
> + for (s = batch_start; s < last_out; s++) {
> + if (s->sensor_id != id)
> + /*
> + * Skip over other sensor types that
> + * are interleaved, don't count them.
> + */
> + continue;
> + if (s->timestamp != batch_timestamp)
> + /* we discovered the next batch */
> + break;
> + if (s->flag & MOTIONSENSE_SENSOR_FLAG_FLUSH)
> + /* break on flush packets */
> + break;
> + batch_end = s;
> + batch_len++;
> + }
> +
> + if (batch_len == 1)
> + goto done_with_this_batch;
> +
> + /* Can we calculate period? */
> + if (sensorhub->last_batch_len[id] == 0) {
> + dev_warn(sensorhub->dev, "Sensor %d: lost %d samples when spreading\n",
> + id, batch_len - 1);
> + goto done_with_this_batch;
> + /*
> + * Note: we're dropping the rest of the samples
> + * in this batch since we have no idea where
> + * they're supposed to go without a period
> + * calculation.
> + */
> + }
> +
> + sample_period = div_s64(batch_timestamp -
> + sensorhub->last_batch_timestamp[id],
> + sensorhub->last_batch_len[id]);
> + dev_dbg(sensorhub->dev,
> + "Adjusting %d samples, sensor %d last_batch @%lld (%d samples) batch_timestamp=%lld => period=%lld\n",
> + batch_len, id,
> + sensorhub->last_batch_timestamp[id],
> + sensorhub->last_batch_len[id],
> + batch_timestamp,
> + sample_period);
> +
> + /*
> + * Adjust timestamps of the samples then push them to
> + * kfifo.
> + */
> + for (s = batch_start; s <= batch_end; s++) {
> + if (s->sensor_id != id)
> + /*
> + * Skip over other sensor types that
> + * are interleaved, don't change them.
> + */
> + continue;
> +
> + s->timestamp = batch_timestamp +
> + sample_period * sample_idx;
> + sample_idx++;
> +
> + cros_sensorhub_send_sample(sensorhub, s);
> + }
> +
> +done_with_this_batch:
> + sensorhub->penultimate_batch_timestamp[id] =
> + sensorhub->last_batch_timestamp[id];
> + sensorhub->penultimate_batch_len[id] =
> + sensorhub->last_batch_len[id];
> +
> + sensorhub->last_batch_timestamp[id] = batch_timestamp;
> + sensorhub->last_batch_len[id] = batch_len;
> +
> + next_batch_start = batch_end + 1;
> + }
> + }
> +}
> +
> +/*
> + * cros_ec_ring_spread_add_legacy: Calculate proper timestamps then
> * add to ringbuffer (legacy).
> *
> + * Note: This assumes we're running old firmware, where every sample's timestamp
> + * is after the sample. Run if tight_timestamps == false.
> + *
> * If there is a sample with a proper timestamp
> * timestamp | count
> * older_unprocess_out --> TS1 | 1
> @@ -208,7 +668,8 @@ static bool cros_ec_ring_process_event(struct cros_ec_sensorhub *sensorhub,
> * 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,
> +static void cros_ec_ring_spread_add_legacy(
> + struct cros_ec_sensorhub *sensorhub,
> unsigned long sensor_mask,
> s64 current_timestamp,
> struct cros_ec_sensors_ring_sample *last_out)
> @@ -277,7 +738,7 @@ static void cros_ec_ring_spread_add(struct cros_ec_sensorhub *sensorhub,
> cros_sensorhub_send_sample(sensorhub, out);
> }
>
> -/*
> +/**

Unrelated change in this patch. Please break it out of here..

> * cros_ec_sensorhub_ring_handler - the trigger handler function
> *
> * @sensorhub: device information.
> @@ -394,7 +855,8 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
> * 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)
> + if (!sensorhub->tight_timestamps &&
> + (last_out - 1)->timestamp == current_timestamp)
> current_timestamp = fifo_timestamp;
>
> /* Warn on lost samples. */
> @@ -408,6 +870,7 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
> dev_warn_ratelimited(sensorhub->dev,
> "Sensor %d: lost: %d out of %d\n",
> i, lost, total_lost);
> + sensorhub->last_batch_len[i] = 0;
> }
> }
> }
> @@ -415,8 +878,11 @@ static void cros_ec_sensorhub_ring_handler(struct cros_ec_sensorhub *sensorhub)
> /*
> * Spread samples in case of batching, then add them to the ringbuffer.
> */
> - cros_ec_ring_spread_add(sensorhub, sensor_mask,
> - current_timestamp, last_out);
> + if (sensorhub->tight_timestamps)
> + cros_ec_ring_spread_add(sensorhub, sensor_mask, last_out);
> + else
> + cros_ec_ring_spread_add_legacy(sensorhub, sensor_mask,
> + current_timestamp, last_out);
>
> ring_handler_end:
> sensorhub->fifo_timestamp[CROS_EC_SENSOR_LAST_TS] = current_timestamp;
> @@ -489,6 +955,9 @@ int cros_ec_sensorhub_ring_add(struct cros_ec_sensorhub *sensorhub)
> sensorhub->fifo_timestamp[CROS_EC_SENSOR_LAST_TS] =
> cros_ec_get_time_ns();
>
> + sensorhub->tight_timestamps = cros_ec_check_features(ec,
> + EC_FEATURE_MOTION_SENSE_TIGHT_TIMESTAMPS);
> +
> /* register the notifier that will act as a top half interrupt. */
> sensorhub->notifier.notifier_call = cros_ec_sensorhub_event;
> ret = blocking_notifier_chain_register(&ec->ec_dev->event_notifier,
> diff --git a/include/linux/platform_data/cros_ec_sensorhub.h b/include/linux/platform_data/cros_ec_sensorhub.h
> index 8f9bf9a70701..e9da92fb0bea 100644
> --- a/include/linux/platform_data/cros_ec_sensorhub.h
> +++ b/include/linux/platform_data/cros_ec_sensorhub.h
> @@ -68,7 +68,44 @@ 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_sensorhub - Sensor Hub device data.
> *
> * @dev: Device object, mostly used for logging.
> @@ -83,6 +120,28 @@ struct cros_ec_sensors_ring_sample {
> * @timestamp: array for event timestamp and spreading.
> * @fifo_info: copy of FIFO information coming from the EC.
> * @fifo_size: size of the ring.
> + *
> + * @penultimate_batch_timestamp: array of last but one batch timestamps.
> + * Used for timestamp spreading calculations when a batch shows up.
> + * @penultimate_batch_len: array of last but one batch length.
> + * @last_batch_timestamp: last batch timestamp array.
> + * @last_batch_len: last batch length array.
> + * @newest_sensor_event: last sensor timestamp.
> + * @overflow_a: for handling timestamp overflow for a time (sensor events)
> + * @overflow_b: for handling timestamp overflow for b time (ec interrutps)

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 occures 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.
> + *
> * @pushdata: array of callback to send datums to iio sensor object.
> */
> struct cros_ec_sensorhub {
> @@ -103,6 +162,22 @@ struct cros_ec_sensorhub {
> struct cros_ec_fifo_info fifo_info;
> int fifo_size;
>
> + s64 penultimate_batch_timestamp[CROS_EC_SENSOR_MAX];
> + int penultimate_batch_len[CROS_EC_SENSOR_MAX];
> + s64 last_batch_timestamp[CROS_EC_SENSOR_MAX];
> + int last_batch_len[CROS_EC_SENSOR_MAX];
> + s64 newest_sensor_event[CROS_EC_SENSOR_MAX];
> +
> + 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;
> +
> + bool tight_timestamps;
> +
> + s32 future_timestamp_count;
> + s64 future_timestamp_total_ns;
> +
> struct cros_ec_sensorhub_sensor_push_data push_data[
> CROS_EC_SENSOR_PDEV_MAX];
> };