Re: [PATCH v4 6/8] iio: imu: adis16607: Add FIFO-based buffered/triggered capture

[Jonathan Cameron]

On Fri, 23 Oct 2026 12:30:23 +0300
Radu Sabau via B4 Relay <devnull+radu.sabau.analog.com@xxxxxxxxxx> wrote:

> From: Radu Sabau <radu.sabau@xxxxxxxxxx>
> 
> Add buffered capture via the device's hardware FIFO - the only
> capture mode this driver supports. Popping the FIFO uses a dedicated
> command and payload format (FIFO_DATA_CMD, 52 bytes, no checksum),
> handled directly rather than through adislib's generic burst-read
> helpers, which assume one fixed-shape read per trigger rather than a
> variable-count drain loop.
> 
> The watermark-met condition is signaled via DEV_NOK on the device's
> one interrupt pin, which stays asserted (level-triggered) until
> DIAG_STAT is read and cleared - matching adislib's has_fifo contract.
> DEV_NOK fires on any DIAG_STAT flag, not just FIFO_THRESH_MET, so the
> trigger handler checks that specific bit before popping anything.
> DR_GPIO_MASK stays enabled unconditionally: DR pulses drive the FIFO
> controller's internal sample enqueue, independent of pin routing.
> 
> Watermark is configurable via the standard hwfifo_set_watermark
> callback and the usual hwfifo_* sysfs attributes.
> 
> Signed-off-by: Radu Sabau <radu.sabau@xxxxxxxxxx>
> ---
>  drivers/iio/imu/adis16607.c | 349 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 346 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iio/imu/adis16607.c b/drivers/iio/imu/adis16607.c
> index 2dda306d7b54..b1f3667d8ce3 100644
> --- a/drivers/iio/imu/adis16607.c
> +++ b/drivers/iio/imu/adis16607.c

>  /* Self-test registers and masks */
>  #define ADIS16607_REG_SELF_TEST_DATA(x)	((x) + 0x23)
>  #define ADIS16607_SNSR_SELF_TEST_MASK	BIT(6)
> @@ -86,6 +110,11 @@ struct adis16607 {
>  	const struct adis16607_chip_info *info;
>  	unsigned long clk_freq_mhz;
>  	u64 sample_period_ns;
> +	u16 fifo_watermark;
> +	/* Scratch buffer used for FIFO pop operations, see adis16607_fifo_pop() */
> +	u8 fifo_buf[ADIS16607_BURST_CMD_SIZE + ADIS16607_FIFO_DATA_LEN] __aligned(IIO_DMA_MINALIGN);
> +	/* IIO buffer for reordered data - sized for max channels */

That rather implies you never DMA into it.  If so just move it before
the fifo_buf and no need to mark it IIO_DMA_MINALIGN.
I'd also prefer that 64 was sized by maths, not a comment saying
it is big enough. That may include use of IIO_DECLARE_BUFFER_WITH_TS()
to ensure the timestamp spacing is there.


> +	u8 data[64] __aligned(IIO_DMA_MINALIGN);
>  };

> +/*
> + * Process a single FIFO sample and push to IIO buffer.
> + * FIFO data format differs from regular burst - no DIAG_STAT, data starts immediately.
> + *
> + * FIFO data layout (52 bytes):
> + *   Offset 0-3:   ACCEL_X (32-bit)
> + *   Offset 4-7:   ACCEL_Y (32-bit)
> + *   Offset 8-11:  ACCEL_Z (32-bit)
> + *   Offset 12-15: GYRO_X (32-bit)
> + *   Offset 16-19: GYRO_Y (32-bit)
> + *   Offset 20-23: GYRO_Z (32-bit)
> + *   Offset 24-27: DELTVEL_X (32-bit)
> + *   Offset 28-31: DELTVEL_Y (32-bit)
> + *   Offset 32-35: DELTVEL_Z (32-bit)
> + *   Offset 36-39: DELTANG_X (32-bit)
> + *   Offset 40-43: DELTANG_Y (32-bit)
> + *   Offset 44-47: DELTANG_Z (32-bit)
> + *   Offset 48-49: TEMP (16-bit)
> + *   Offset 50-51: DATA_CNTR (16-bit)
> + */
> +static void adis16607_fifo_push_sample(struct iio_dev *indio_dev,
> +				       u8 *fifo_data, s64 timestamp)
> +{
> +	struct adis16607 *st = iio_priv(indio_dev);
> +	u16 msw, lsw;
> +	s32 val24;
> +	int bit, offset = 0;
> +
> +	memset(st->data, 0, sizeof(st->data));
> +
> +	for_each_set_bit(bit, indio_dev->active_scan_mask, indio_dev->masklength) {
iio_for_each_active_channel()

As sashiko notes, masklength is private.

There are a load of places we need to update to stop accessing these
directly but please don't add another one.

It's on my list to throw some LLM tokens ago once I get out from
under review backlog.

https://sashiko.dev/#/patchset/20261023-adis16607-v4-0-a4d541ebfd13%40analog.com
Check everything else reported.

FWIW there are also some nasty race conditions around active_scan_mask
being available when the buffer is being torn down. You might
want to close those off by claiming buffered mode to prevent
such a transition.

> +		u8 burst_off;
> +
> +		/* Skip the soft timestamp channel - it has no burst offset */
> +		if (bit >= ARRAY_SIZE(adis16607_burst_offsets))
> +			continue;
> +
> +		burst_off = adis16607_burst_offsets[bit];
> +
> +		if (bit == ADIS16607_SCAN_TEMP) {
> +			/* TEMP is 16-bit */
> +			put_unaligned_be16(get_unaligned_be16(&fifo_data[burst_off]),
> +					   &st->data[offset]);
> +			offset += 2;
> +		} else {
> +			/* All other channels are 24-bit stored as 32-bit */
> +			msw = get_unaligned_be16(&fifo_data[burst_off]);
> +			lsw = get_unaligned_be16(&fifo_data[burst_off + 2]);
> +			val24 = sign_extend32(((u32)msw << 8) | (lsw >> 8), 23);
> +			put_unaligned_be32(val24, &st->data[offset]);
> +			offset += 4;
> +		}
> +	}
> +
> +	iio_push_to_buffers_with_timestamp(indio_dev, st->data, timestamp);
Use iio_push_to_buffers_with_ts() as for once in an ADIS driver we actually
have the size of data.  Note that fixing the whole adis library is something
that needs doing though I took a look at it on Friday and decided to leave
it for now!

Jonathan

> +}