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    SubjectRe: [PATCH 03/16] iio: adc: max1027: Push only the requested samples
    On Mon, 30 Aug 2021 10:49:50 +0000
    "Sa, Nuno" <Nuno.Sa@analog.com> wrote:

    > > -----Original Message-----
    > > From: Jonathan Cameron <jic23@kernel.org>
    > > Sent: Monday, August 30, 2021 12:08 PM
    > > To: Sa, Nuno <Nuno.Sa@analog.com>
    > > Cc: Miquel Raynal <miquel.raynal@bootlin.com>; Lars-Peter Clausen
    > > <lars@metafoo.de>; Thomas Petazzoni
    > > <thomas.petazzoni@bootlin.com>; linux-iio@vger.kernel.org; linux-
    > > kernel@vger.kernel.org
    > > Subject: Re: [PATCH 03/16] iio: adc: max1027: Push only the requested
    > > samples
    > >
    > > [External]
    > >
    > > On Fri, 20 Aug 2021 07:10:48 +0000
    > > "Sa, Nuno" <Nuno.Sa@analog.com> wrote:
    > >
    > > > > -----Original Message-----
    > > > > From: Miquel Raynal <miquel.raynal@bootlin.com>
    > > > > Sent: Wednesday, August 18, 2021 1:11 PM
    > > > > To: Jonathan Cameron <jic23@kernel.org>; Lars-Peter Clausen
    > > > > <lars@metafoo.de>
    > > > > Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>; linux-
    > > > > iio@vger.kernel.org; linux-kernel@vger.kernel.org; Miquel Raynal
    > > > > <miquel.raynal@bootlin.com>
    > > > > Subject: [PATCH 03/16] iio: adc: max1027: Push only the requested
    > > > > samples
    > > > >
    > > > > [External]
    > > > >
    > > > > 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 but only the desired channels will be pushed
    > > to
    > > > > the IIO buffers.
    > > > >
    > > > > Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
    > > > > ---
    > > > > 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;
    > > > > +
    > > >
    > > > I'm not sure this can actually happen. If you try to enable the buffer
    > > > with no scan element, it should give you an error before you reach
    > > > this point...
    > > >
    > > > > 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);
    > > > > 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;
    > > >
    > > > I think sparse will complain here. buffer is a __be16 restricted
    > > > type so you should not mix those...
    > > > > + unsigned int bit;
    > > > >
    > > > > pr_debug("%s(irq=%d, private=0x%p)\n", __func__, irq,
    > > > >
    > > private);in/20210818_miquel_raynal_bring_software_triggers_support
    > > _to_max1027_like_adcs.mbx
    > > > >
    > > > > /* 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];
    > > >
    > > > Since we are here, when looking into the driver, I realized
    > > > that st->buffer is not DMA safe. In IIO, we kind of want to enforce
    > > > that all buffers that are passed to spi/i2c buses are safe... Maybe
    > > > this is something you can include in your series.
    > >
    > > Why is it not? st->buffer is result of a devm_kmalloc_array() call and
    > > that should provide a DMA safe buffer as I understand it.
    > >
    >
    > That's a good question. I'm not sure how I came to that conclusion which
    > is clearly wrong. Though I think the buffer might share the line with the
    > mutex...
    Pointer shares a line. The buffer it points to doesn't as allocated
    by separate heap allocation.

    J
    >
    > - Nuno Sá
    >

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