On Wed, 18 Aug 2021 13:11:26 +0200
Miquel Raynal <miquel.raynal@xxxxxxxxxxx> wrote:
> When a triggered scan occurs, the identity of the desired channels is
> known in indio_dev->active_scan_mask. Instead of reading and pushing to
> the IIO buffers all channels each time, scan the minimum amount of
> channels (0 to maximum requested chan, to be exact) and only provide the
> samples requested by the user.
>
> For example, if the user wants channels 1, 4 and 5, all channels from
> 0 to 5 will be scanned
That's a reasonably optimisation
> but only the desired channels will be pushed to
> the IIO buffers.
Don't do this last bit. The core handles demuxing the channels via
active_scan_masks. As a general rule it does a more efficient job of this
than a hand coded version in a driver (precached copy rules etc).
The core has to have the logic anyway to support multiple consumers
(e.g. in kernel consumer and userspace) so we reuse it for these cases.
>
> Signed-off-by: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> ---
> drivers/iio/adc/max1027.c | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c
> index b753658bb41e..8ab660f596b5 100644
> --- a/drivers/iio/adc/max1027.c
> +++ b/drivers/iio/adc/max1027.c
> @@ -360,6 +360,9 @@ static int max1027_set_trigger_state(struct iio_trigger *trig, bool state)
> struct max1027_state *st = iio_priv(indio_dev);
> int ret;
>
> + if (bitmap_empty(indio_dev->active_scan_mask, indio_dev->masklength))
> + return -EINVAL;
> +
> if (state) {
> /* Start acquisition on cnvst */
> st->reg = MAX1027_SETUP_REG | MAX1027_CKS_MODE0 |
> @@ -368,9 +371,12 @@ static int max1027_set_trigger_state(struct iio_trigger *trig, bool state)
> if (ret < 0)
> return ret;
>
> - /* Scan from 0 to max */
> - st->reg = MAX1027_CONV_REG | MAX1027_CHAN(0) |
> - MAX1027_SCAN_N_M | MAX1027_TEMP;
> + /*
> + * Scan from 0 to the highest requested channel. The temperature
> + * could be avoided but it simplifies a bit the logic.
> + */
> + st->reg = MAX1027_CONV_REG | MAX1027_SCAN_0_N | MAX1027_TEMP;
> + st->reg |= MAX1027_CHAN(fls(*indio_dev->active_scan_mask) - 2);
This should be combined with appropriate additions to available_scan_masks arrays
so the IIO core can handle choosing the right one to match enabled channels.
> ret = spi_write(st->spi, &st->reg, 1);
> if (ret < 0)
> return ret;
> @@ -391,11 +397,22 @@ static irqreturn_t max1027_trigger_handler(int irq, void *private)
> struct iio_poll_func *pf = private;
> struct iio_dev *indio_dev = pf->indio_dev;
> struct max1027_state *st = iio_priv(indio_dev);
> + unsigned int scanned_chans = fls(*indio_dev->active_scan_mask);
> + u16 *buf = st->buffer;
> + unsigned int bit;
>
> pr_debug("%s(irq=%d, private=0x%p)\n", __func__, irq, private);
>
> /* fill buffer with all channel */
> - spi_read(st->spi, st->buffer, indio_dev->masklength * 2);
> + spi_read(st->spi, st->buffer, scanned_chans * 2);
> +
> + /* Only keep the channels selected by the user */
> + for_each_set_bit(bit, indio_dev->active_scan_mask,
> + indio_dev->masklength) {
> + if (buf[0] != st->buffer[bit])
> + buf[0] = st->buffer[bit];
> + buf++;
> + }
>
> iio_push_to_buffers(indio_dev, st->buffer);
>
