linux-kernel - Re: [PATCH v2 05/16] iio: adc: max1027: Minimize the number of converted channels

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Message-ID: <20210905163406.4d4d86a0@jic23-huawei>
Date:   Sun, 5 Sep 2021 16:34:06 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Miquel Raynal <miquel.raynal@...tlin.com>
Cc:     Lars-Peter Clausen <lars@...afoo.de>, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Nuno Sa <Nuno.Sa@...log.com>
Subject: Re: [PATCH v2 05/16] iio: adc: max1027: Minimize the number of
 converted channels

On Thu,  2 Sep 2021 23:14:26 +0200
Miquel Raynal <miquel.raynal@...tlin.com> wrote:

> Provide a list of ->available_scan_masks which match the device's
> capabilities. Basically, the devices is able to scan from 0 to N, N
> being the highest voltage channel requested by the user. The temperature
> can be included or not, but cannot be retrieved alone.
> 
> The consequence is, instead of reading and pushing to the IIO buffers
> all channels each time, the "minimum" number of channels will be scanned
> and pushed based on the ->active_scan_mask.
> 
> For example, if the user wants channels 1, 4 and 5, all channels from
> 0 to 5 will be scanned and pushed to the IIO buffers. The core will then
> filter out the unneeded samples based on the ->active_scan_mask that has
> been selected and only channels 1, 4 and 5 will be available to the user
> in the shared buffer.

This explanation is excellent.  If you are respinning it would be great
to have the essence of it as a comment alongside the code.
The bit about temp in particular was something I'd missed.

Nice optimization in general.

Jonathan
 
> 
> Signed-off-by: Miquel Raynal <miquel.raynal@...tlin.com>
> ---
>  drivers/iio/adc/max1027.c | 46 +++++++++++++++++++++++++++++++++------
>  1 file changed, 39 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/iio/adc/max1027.c b/drivers/iio/adc/max1027.c
> index 1167d50c1d67..3c41d2c0ed2a 100644
> --- a/drivers/iio/adc/max1027.c
> +++ b/drivers/iio/adc/max1027.c
> @@ -172,18 +172,39 @@ static const struct iio_chan_spec max1231_channels[] = {
>  	MAX1X31_CHANNELS(12),
>  };
>  
> +#define MAX1X27_SCAN_MASK_TEMP BIT(0)
> +
> +#define MAX1X27_SCAN_MASKS(temp)					\
> +	GENMASK(1, 1 - (temp)), GENMASK(2, 1 - (temp)),			\
> +	GENMASK(3, 1 - (temp)), GENMASK(4, 1 - (temp)),			\
> +	GENMASK(5, 1 - (temp)), GENMASK(6, 1 - (temp)),			\
> +	GENMASK(7, 1 - (temp)), GENMASK(8, 1 - (temp))
> +
> +#define MAX1X29_SCAN_MASKS(temp)					\
> +	MAX1X27_SCAN_MASKS(temp),					\
> +	GENMASK(9, 1 - (temp)), GENMASK(10, 1 - (temp)),		\
> +	GENMASK(11, 1 - (temp)), GENMASK(12, 1 - (temp))
> +
> +#define MAX1X31_SCAN_MASKS(temp)					\
> +	MAX1X29_SCAN_MASKS(temp),					\
> +	GENMASK(13, 1 - (temp)), GENMASK(14, 1 - (temp)),		\
> +	GENMASK(15, 1 - (temp)), GENMASK(16, 1 - (temp))
> +
>  static const unsigned long max1027_available_scan_masks[] = {
> -	0x000001ff,
> +	MAX1X27_SCAN_MASKS(0),
> +	MAX1X27_SCAN_MASKS(1),
>  	0x00000000,
>  };
>  
>  static const unsigned long max1029_available_scan_masks[] = {
> -	0x00001fff,
> +	MAX1X29_SCAN_MASKS(0),
> +	MAX1X29_SCAN_MASKS(1),
>  	0x00000000,
>  };
>  
>  static const unsigned long max1031_available_scan_masks[] = {
> -	0x0001ffff,
> +	MAX1X31_SCAN_MASKS(0),
> +	MAX1X31_SCAN_MASKS(1),
>  	0x00000000,
>  };
>  
> @@ -368,9 +389,15 @@ 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 chan 0 to the highest requested channel.
> +		 * Include temperature on demand.
> +		 */
> +		st->reg = MAX1027_CONV_REG | MAX1027_SCAN_0_N;
> +		st->reg |= MAX1027_CHAN(fls(*indio_dev->active_scan_mask) - 2);
> +		if (*indio_dev->active_scan_mask & MAX1X27_SCAN_MASK_TEMP)
> +			st->reg |= MAX1027_TEMP;
> +
>  		ret = spi_write(st->spi, &st->reg, 1);
>  		if (ret < 0)
>  			return ret;
> @@ -391,9 +418,14 @@ 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;
> +
> +	scanned_chans = fls(*indio_dev->active_scan_mask) - 1;
> +	if (*indio_dev->active_scan_mask & MAX1X27_SCAN_MASK_TEMP)
> +		scanned_chans++;
>  
>  	/* fill buffer with all channel */
> -	spi_read(st->spi, st->buffer, indio_dev->masklength * 2);
> +	spi_read(st->spi, st->buffer, scanned_chans * 2);
>  
>  	iio_push_to_buffers(indio_dev, st->buffer);
>