Date: Mon, 06 May 2024 10:33:23 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Julien Stephan <jstephan@...libre.com>, Lars-Peter Clausen
 <lars@...afoo.de>,  Michael Hennerich <Michael.Hennerich@...log.com>, Nuno
 Sá <nuno.sa@...log.com>, David Lechner
 <dlechner@...libre.com>, Jonathan Cameron <jic23@...nel.org>, Rob Herring
 <robh@...nel.org>, Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
  Conor Dooley <conor+dt@...nel.org>, Liam Girdwood <lgirdwood@...il.com>,
 Mark Brown <broonie@...nel.org>
Cc: kernel test robot <lkp@...el.com>, linux-iio@...r.kernel.org, 
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v6 09/10] iio: adc: ad7380: add support for rolling
 average oversampling mode

On Wed, 2024-05-01 at 16:55 +0200, Julien Stephan wrote:
> Adds support for rolling average oversampling mode.
> 
> Rolling oversampling mode uses a first in, first out (FIFO) buffer of
> the most recent samples in the averaging calculation, allowing the ADC
> throughput rate and output data rate to stay the same, since we only need
> to take only one sample for each new conversion.
> 
> The FIFO length is 8, thus the available oversampling ratios are 1, 2, 4, 8
> in this mode (vs 1,  2, 4, 8, 16, 32 for the normal average)
> 
> In order to be able to change the averaging mode, this commit also adds
> the new "oversampling_mode" and "oversampling_mode_available" custom
> attributes along with the according documentation file in
> Documentation/ABI/testing/sysfs-bus-iio-adc-ad7380 since no standard
> attributes correspond to this use case.
> 
> Signed-off-by: Julien Stephan <jstephan@...libre.com>
> ---
>  Documentation/ABI/testing/sysfs-bus-iio-adc-ad7380 |  38 ++++++
>  MAINTAINERS                                        |   1 +
>  drivers/iio/adc/ad7380.c                           | 143 +++++++++++++++++++--
>  3 files changed, 174 insertions(+), 8 deletions(-)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-iio-adc-ad7380
> b/Documentation/ABI/testing/sysfs-bus-iio-adc-ad7380
> new file mode 100644
> index 000000000000..0a560ef3e32a
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-bus-iio-adc-ad7380
> @@ -0,0 +1,38 @@
> +What: /sys/bus/iio/devices/iio:deviceX/oversampling_mode
> +KernelVersion: 6.9
> +Contact: Michael Hennerich <michael.hennerich@...log.com>
> +Description:
> +    Writing this attribute sets the oversampling average mode.
> +    Reading it, shows the configured mode.
> +    Available modes can be displayed using the oversampling_mode_available
> +    attribute.
> +    When writing this attribute to change the oversampling mode, this will
> +    have the following side effects:
> +
> +      - soft reset the ADC to flush the oversampling block and FIFO
> +
> +      - the available oversampling ratios depend on the oversampling mode
> +        configured so to avoid misconfiguration, changing the mode will disable
> +        the oversampling by setting the ratio to 1.

Hmm, can we somehow re-enable it again with a proper configuration (after the mode
change)?

> +
> +      - the list of available ratios (displayed by reading the
> +        oversampling_ratio_available attribute) will be updated when changing
> +        the oversampling mode.
> +
> +What: /sys/bus/iio/devices/iio:deviceX/oversampling_mode_available
> +KernelVersion: 6.9
> +Contact: Michael Hennerich <michael.hennerich@...log.com>
> +Description:
> +    Display the available oversampling average modes. The two available modes
> +    are "normal" and "rolling" where "normal" average mode is the default one.
> +
> +      - normal averaging involves taking a number of samples, adding them
> +        together, and dividing the result by the number of samples taken.
> +        This result is then output from the device. The sample data is cleared
> +        when the process completes. Because we need more samples to output a
> +        value, the data output rate decrease with the oversampling ratio.
> +
> +      - rolling oversampling mode uses a first in, first out (FIFO) buffer of
> +        the most recent samples in the averaging calculation, allowing the ADC
> +        throughput rate and output data rate to stay the same, since we only need
> +        to take only one sample for each new conversion.
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 87724a9e9f9f..ca1e115f2aff 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -434,6 +434,7 @@ R:	David Lechner <dlechner@...libre.com>
>  S:	Supported
>  W:	
> https://wiki.analog.com/resources/tools-software/linux-drivers/iio-adc/ad738x
>  W:	https://ez.analog.com/linux-software-drivers
> +F:	Documentation/ABI/testing/sysfs-bus-iio-adc-ad7380
>  F:	Documentation/devicetree/bindings/iio/adc/adi,ad7380.yaml
>  F:	drivers/iio/adc/ad7380.c
>  
> diff --git a/drivers/iio/adc/ad7380.c b/drivers/iio/adc/ad7380.c
> index 1e3869f5e48c..7b021bb9cf87 100644
> --- a/drivers/iio/adc/ad7380.c
> +++ b/drivers/iio/adc/ad7380.c
> @@ -51,6 +51,8 @@
>  #define AD7380_REG_ADDR_ALERT_HIGH_TH	0x5
>  
>  #define AD7380_CONFIG1_OS_MODE		BIT(9)
> +#define OS_MODE_NORMAL_AVERAGE		0
> +#define OS_MODE_ROLLING_AVERAGE		1

no AD7380 prefix?

>  #define AD7380_CONFIG1_OSR		GENMASK(8, 6)
>  #define AD7380_CONFIG1_CRC_W		BIT(5)
>  #define AD7380_CONFIG1_CRC_R		BIT(4)
> @@ -159,16 +161,27 @@ static const struct ad7380_timing_specs ad7380_4_timing = {
>  	.t_csh_ns = 20,
>  };
>  

..

> 
> +static ssize_t oversampling_mode_store(struct device *dev,
> +				       struct device_attribute *attr,
> +				       const char *buf, size_t len)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct ad7380_state *st = iio_priv(indio_dev);
> +	int os_mode, ret;
> +
> +	ret = sysfs_match_string(ad7380_oversampling_average_modes, buf);
> +	if (ret < 0)
> +		return ret;
> +
> +	os_mode = ret;
> +
> +	iio_device_claim_direct_scoped(return -EBUSY, indio_dev) {
> +		ret = regmap_update_bits(st->regmap, AD7380_REG_ADDR_CONFIG1,
> +					 AD7380_CONFIG1_OS_MODE,
> +					 FIELD_PREP(AD7380_CONFIG1_OS_MODE,
> os_mode));
> +
> +		if (ret)
> +			return  ret;
> +
> +		st->oversampling_mode = os_mode;
> +
> +		/*
> +		 * Oversampling ratio depends on oversampling mode, to avoid
> +		 * misconfiguration when changing oversampling mode,
> +		 * disable oversampling by setting OSR to 0.
> +		 */

Given the comment, I would expect you to disable osr before changing the mode.

> +		ret = regmap_update_bits(st->regmap, AD7380_REG_ADDR_CONFIG1,
> +					 AD7380_CONFIG1_OSR,
> FIELD_PREP(AD7380_CONFIG1_OSR, 0));
> +
> +		if (ret)
> +			return ret;
> +
> +		st->oversampling_ratio = 1;
> +

1?

Also, it would be nice if we could re-enabled osr. So the flow would maybe be:

1) disable osr;
2) change mode;
3) do whatever we need so configuration makes sense for new mode?
4) re-enable osr;
5) soft-reset;

Also not sure if 4) and 5) are in the correct order.

> +		/*
> +		 * Perform a soft reset.
> +		 * This will flush the oversampling block and FIFO but will
> +		 * maintain the content of the configurable registers.
> +		 */
> +		ret = regmap_update_bits(st->regmap, AD7380_REG_ADDR_CONFIG2,
> +					 AD7380_CONFIG2_RESET,
> +					 FIELD_PREP(AD7380_CONFIG2_RESET,
> +						    AD7380_CONFIG2_RESET_SOFT));
> +	}
> +	return ret ?: len;
> +}
> +
> +static ssize_t oversampling_mode_available_show(struct device *dev,
> +						struct device_attribute *attr,
> char *buf)
> +{
> +	int i;
> +	size_t len = 0;
> +
> +	for (i = 0; i < ARRAY_SIZE(ad7380_oversampling_average_modes); i++)
> +		len += sysfs_emit_at(buf, len, "%s ",
> ad7380_oversampling_average_modes[i]);
> +
> +	buf[len - 1] = '\n';
> +
> +	return len;
> +}
> +
> +static IIO_DEVICE_ATTR_RW(oversampling_mode, 0);
> +static IIO_DEVICE_ATTR_RO(oversampling_mode_available, 0);
> +
> +static struct attribute *ad7380_attributes[] = {
> +	&iio_dev_attr_oversampling_mode.dev_attr.attr,
> +	&iio_dev_attr_oversampling_mode_available.dev_attr.attr,
> +	NULL
> +};
> +

Maybe use IIO_ENUM... It allows the core to do some of the stuff you're doing for
you.


- Nuno Sá

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