Re: [PATCH 2/2] iio: imu: st_lsm6dsx: add iio trigger and buffer support

[Jonathan Cameron <jic23@kernel.org>]

On Tue,  7 May 2019 10:02:25 +0200
Sean Nyekjaer <sean@geanix.com> wrote:

> This adds support for using iio triggers, this is needed because
> our hardware guys forgot to connect the irq pins from imu device
> to the SoC.
> 
> Signed-off-by: Sean Nyekjaer <sean@geanix.com>
Hi Sean

A small question on the size of the buffer needed inline.  Otherwise looks
good to me.
> ---
>  drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c | 37 ++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> index 1ca69598678f..65ab853202de 100644
> --- a/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> +++ b/drivers/iio/imu/st_lsm6dsx/st_lsm6dsx_core.c
> @@ -40,8 +40,11 @@
>  #include <linux/kernel.h>
>  #include <linux/module.h>
>  #include <linux/delay.h>
> +#include <linux/iio/buffer.h>
>  #include <linux/iio/iio.h>
>  #include <linux/iio/sysfs.h>
> +#include <linux/iio/trigger_consumer.h>
> +#include <linux/iio/triggered_buffer.h>
>  #include <linux/pm.h>
>  #include <linux/regmap.h>
>  #include <linux/bitfield.h>
> @@ -945,6 +948,30 @@ static int st_lsm6dsx_init_hw_timer(struct st_lsm6dsx_hw *hw)
>  	return 0;
>  }
>  
> +static irqreturn_t st_lsm6dsx_trigger_handler(int irq, void *p)
> +{
> +	struct iio_poll_func *pf = p;
> +	struct iio_dev *indio_dev = pf->indio_dev;
> +	struct st_lsm6dsx_sensor *sensor = iio_priv(indio_dev);
> +	u16 buffer[4 * sizeof(s64)/sizeof(u16)];
The size may well be correct, but that particular way of expressing it doesn't make
it terribly clear.

It seems a bit large... You need the space for the timestamp, so it needs to be
padded to a u64, but that would still require your other channels to need
more than 2*sizeof(s64)/sizeof(u16) u16s which is 9 or more of them.

> +	int tmp, bit;
> +
> +	memset(buffer, 0, sizeof(buffer));
> +
> +	for_each_set_bit(bit, indio_dev->active_scan_mask, indio_dev->masklength) {
> +		st_lsm6dsx_read_oneshot(sensor,
> +					indio_dev->channels[bit].address, &tmp);
> +		buffer[bit] = tmp;
> +	}
> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, buffer,
> +					   iio_get_time_ns(indio_dev));
> +
> +	iio_trigger_notify_done(indio_dev->trig);
> +
> +	return IRQ_HANDLED;
> +}
> +
>  static int st_lsm6dsx_init_device(struct st_lsm6dsx_hw *hw)
>  {
>  	u8 drdy_int_reg;
> @@ -1093,6 +1120,16 @@ int st_lsm6dsx_probe(struct device *dev, int irq, int hw_id, const char *name,
>  		err = st_lsm6dsx_fifo_setup(hw);
>  		if (err < 0)
>  			return err;
> +	} else {
> +		for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {
> +			err = devm_iio_triggered_buffer_setup(hw->dev,
> +					hw->iio_devs[i], NULL,
> +					st_lsm6dsx_trigger_handler, NULL);
> +			if (err < 0) {
> +				dev_err(hw->dev, "iio triggered buffer setup failed\n");
> +				return err;
> +			}
> +		}
>  	}
>  
>  	for (i = 0; i < ST_LSM6DSX_ID_MAX; i++) {