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SubjectRe: [PATCH v3 3/5] iio: srf08: add triggered buffer support
On Wed, 16 Aug 2017 21:34:06 +0200
Andreas Klinger <ak@it-klinger.de> wrote:

> Add support for triggered buffers.
>
> Data format is quite simple:
> distance 16 Bit
> alignment 48 Bit
> timestamp 64 Bit
>
> Signed-off-by: Andreas Klinger <ak@it-klinger.de>

One little improvement I noticed inline that an additional unlocked
reading function would tidy up.

Thanks,

Jonathan
> ---
> drivers/iio/proximity/srf08.c | 60 ++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 57 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/iio/proximity/srf08.c b/drivers/iio/proximity/srf08.c
> index 3f19536f215f..de699d67310a 100644
> --- a/drivers/iio/proximity/srf08.c
> +++ b/drivers/iio/proximity/srf08.c
> @@ -18,6 +18,9 @@
> #include <linux/bitops.h>
> #include <linux/iio/iio.h>
> #include <linux/iio/sysfs.h>
> +#include <linux/iio/buffer.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
>
> /* registers of SRF08 device */
> #define SRF08_WRITE_COMMAND 0x00 /* Command Register */
> @@ -35,9 +38,22 @@
>
> struct srf08_data {
> struct i2c_client *client;
> - int sensitivity; /* Gain */
> - int range_mm; /* max. Range in mm */
> +
> + /*
> + * Gain in the datasheet is called sensitivity here to distinct it
> + * from the gain used with amplifiers of adc's
> + */
> + int sensitivity;
> +
> + /* max. Range in mm */
> + int range_mm;
> struct mutex lock;
> +
> + /*
> + * triggered buffer
> + * 1x16-bit channel + 3x16 padding + 4x16 timestamp
> + */
> + s16 buffer[8];
> };
>
> /*
> @@ -110,6 +126,29 @@ static int srf08_read_ranging(struct srf08_data *data)
> return ret;
> }
>
> +static irqreturn_t srf08_trigger_handler(int irq, void *p)
> +{
> + struct iio_poll_func *pf = p;
> + struct iio_dev *indio_dev = pf->indio_dev;
> + struct srf08_data *data = iio_priv(indio_dev);
> + s16 sensor_data;
> +

There is a bit of lock bouncing going on here where you take the lock
inside srf08_read_ranging drop it at the end and immediately
retake it.

Introduce an unlocked version of read_ranging and hold the lock over
the whole cycle.
> + sensor_data = srf08_read_ranging(data);
> + if (sensor_data < 0)
> + goto err;
> +
> + mutex_lock(&data->lock);
> +
> + data->buffer[0] = sensor_data;
> + iio_push_to_buffers_with_timestamp(indio_dev,
> + data->buffer, pf->timestamp);
> +
> + mutex_unlock(&data->lock);
> +err:
> + iio_trigger_notify_done(indio_dev->trig);
> + return IRQ_HANDLED;
> +}
> +
> static int srf08_read_raw(struct iio_dev *indio_dev,
> struct iio_chan_spec const *channel, int *val,
> int *val2, long mask)
> @@ -323,7 +362,15 @@ static const struct iio_chan_spec srf08_channels[] = {
> .info_mask_separate =
> BIT(IIO_CHAN_INFO_RAW) |
> BIT(IIO_CHAN_INFO_SCALE),
> + .scan_index = 0,
> + .scan_type = {
> + .sign = 's',
> + .realbits = 16,
> + .storagebits = 16,
> + .endianness = IIO_CPU,
> + },
> },
> + IIO_CHAN_SOFT_TIMESTAMP(1),
> };
>
> static const struct iio_info srf08_info = {
> @@ -362,6 +409,13 @@ static int srf08_probe(struct i2c_client *client,
>
> mutex_init(&data->lock);
>
> + ret = devm_iio_triggered_buffer_setup(&client->dev, indio_dev,
> + iio_pollfunc_store_time, srf08_trigger_handler, NULL);
> + if (ret < 0) {
> + dev_err(&client->dev, "setup of iio triggered buffer failed\n");
> + return ret;
> + }
> +
> /*
> * set default values of device here
> * these register values cannot be read from the hardware
> @@ -402,5 +456,5 @@ static struct i2c_driver srf08_driver = {
> module_i2c_driver(srf08_driver);
>
> MODULE_AUTHOR("Andreas Klinger <ak@it-klinger.de>");
> -MODULE_DESCRIPTION("Devantech SRF08 ultrasonic ranger driver");
> +MODULE_DESCRIPTION("Devantech SRF08/SRF10 ultrasonic ranger driver");
> MODULE_LICENSE("GPL");

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