From 8ea2a63869517271f7356241015a3edf3efb77a5 Mon Sep 17 00:00:00 2001 From: Stefan Brüns Date: Mon, 1 Jan 2018 02:24:42 +0100 Subject: iio: adc: ina2xx: Use a monotonic clock for delay calculation MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The iio timestamp clock is user selectable and may be non-monotonic. Also, only part of the acquisition time is measured, thus the delay was longer than intended. Use a monotonic timestamp to track the time for the next poll iteration. The timestamp is advanced by the sampling interval each iteration. In case the conversion overrruns the register readout (i.e. fast sampling combined with a slow bus), one or multiple samples will be dropped. Signed-off-by: Stefan Brüns Signed-off-by: Jonathan Cameron Signed-off-by: Greg Kroah-Hartman --- drivers/iio/adc/ina2xx-adc.c | 41 +++++++++++++++++++++++++++-------------- 1 file changed, 27 insertions(+), 14 deletions(-) (limited to 'drivers/iio') diff --git a/drivers/iio/adc/ina2xx-adc.c b/drivers/iio/adc/ina2xx-adc.c index 94d506f0f404..144d5c950f2b 100644 --- a/drivers/iio/adc/ina2xx-adc.c +++ b/drivers/iio/adc/ina2xx-adc.c @@ -705,10 +705,10 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev) /* data buffer needs space for channel data and timestap */ unsigned short data[4 + sizeof(s64)/sizeof(short)]; int bit, ret, i = 0; - s64 time_a, time_b; + s64 time; unsigned int alert; - time_a = iio_get_time_ns(indio_dev); + time = iio_get_time_ns(indio_dev); /* * Because the timer thread and the chip conversion clock @@ -754,11 +754,9 @@ static int ina2xx_work_buffer(struct iio_dev *indio_dev) data[i++] = val; } - time_b = iio_get_time_ns(indio_dev); + iio_push_to_buffers_with_timestamp(indio_dev, data, time); - iio_push_to_buffers_with_timestamp(indio_dev, data, time_a); - - return (unsigned long)(time_b - time_a) / 1000; + return 0; }; static int ina2xx_capture_thread(void *data) @@ -766,7 +764,9 @@ static int ina2xx_capture_thread(void *data) struct iio_dev *indio_dev = data; struct ina2xx_chip_info *chip = iio_priv(indio_dev); int sampling_us = SAMPLING_PERIOD(chip); - int buffer_us, delay_us; + int ret; + struct timespec64 next, now, delta; + s64 delay_us; /* * Poll a bit faster than the chip internal Fs, in case @@ -775,15 +775,28 @@ static int ina2xx_capture_thread(void *data) if (!chip->allow_async_readout) sampling_us -= 200; + ktime_get_ts64(&next); + do { - buffer_us = ina2xx_work_buffer(indio_dev); - if (buffer_us < 0) - return buffer_us; + ret = ina2xx_work_buffer(indio_dev); + if (ret < 0) + return ret; - if (sampling_us > buffer_us) { - delay_us = sampling_us - buffer_us; - usleep_range(delay_us, (delay_us * 3) >> 1); - } + ktime_get_ts64(&now); + + /* + * Advance the timestamp for the next poll by one sampling + * interval, and sleep for the remainder (next - now) + * In case "next" has already passed, the interval is added + * multiple times, i.e. samples are dropped. + */ + do { + timespec64_add_ns(&next, 1000 * sampling_us); + delta = timespec64_sub(next, now); + delay_us = div_s64(timespec64_to_ns(&delta), 1000); + } while (delay_us <= 0); + + usleep_range(delay_us, (delay_us * 3) >> 1); } while (!kthread_should_stop()); -- cgit v1.2.3