linux-kernel - RE: [PATCH 03/16] iio: adc: max1027: Push only the requested samples

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Date:   Fri, 20 Aug 2021 07:10:48 +0000
From:   "Sa, Nuno" <Nuno.Sa@...log.com>
To:     Miquel Raynal <miquel.raynal@...tlin.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>
CC:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        "linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 03/16] iio: adc: max1027: Push only the requested samples



> -----Original Message-----
> From: Miquel Raynal <miquel.raynal@...tlin.com>
> Sent: Wednesday, August 18, 2021 1:11 PM
> To: Jonathan Cameron <jic23@...nel.org>; Lars-Peter Clausen
> <lars@...afoo.de>
> Cc: Thomas Petazzoni <thomas.petazzoni@...tlin.com>; linux-
> iio@...r.kernel.org; linux-kernel@...r.kernel.org; Miquel Raynal
> <miquel.raynal@...tlin.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@...tlin.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);
> 
>  	/* 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.

- Nuno Sá

 > +		buf++;
> +	}
> 
>  	iio_push_to_buffers(indio_dev, st->buffer);
> 
> --
> 2.27.0