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Date:   Sun, 26 May 2019 18:45:07 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Fabien Lahoudere <fabien.lahoudere@...labora.com>
Cc:     kernel@...labora.com, Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        Benson Leung <bleung@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Guenter Roeck <groeck@...omium.org>,
        Lee Jones <lee.jones@...aro.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] iio: common: cros_ec_sensors: add sysfs
 attribute for frequencies

On Thu, 23 May 2019 11:07:36 +0200
Fabien Lahoudere <fabien.lahoudere@...labora.com> wrote:

> In order to provide minimum and maximum frequencies for each sensors,
> we use a standard API (sampling_frequency_available) to provide them
> to userland.
> As cros_ec_sensors_core_init do not manage default attrs, we change
> the signature to let all kind of sensors to provide "struct iio_info"
> with their callback. This change impact drivers using that function.
> 
> Then cros_ec_* sensors provides frequencies range in sysfs like this:
> [min step max]
> 
> Signed-off-by: Fabien Lahoudere <fabien.lahoudere@...labora.com>
When I was pointing at the _available syntax I was meaning that
the ideal is to implement this using the associated callbacks rather
than as a custom sysfs attribute.

> ---
>  .../common/cros_ec_sensors/cros_ec_sensors.c  |  6 +--
>  .../cros_ec_sensors/cros_ec_sensors_core.c    | 38 +++++++++++++++++++
>  drivers/iio/light/cros_ec_light_prox.c        |  6 +--
>  drivers/iio/pressure/cros_ec_baro.c           |  6 +--
>  .../linux/iio/common/cros_ec_sensors_core.h   |  4 +-
>  5 files changed, 50 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
> index 17af4e0fd5f8..a0ecee15a6c8 100644
> --- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
> +++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors.c
> @@ -172,7 +172,7 @@ static int cros_ec_sensors_write(struct iio_dev *indio_dev,
>  	return ret;
>  }
>  
> -static const struct iio_info ec_sensors_info = {
> +static struct iio_info ec_sensors_info = {
>  	.read_raw = &cros_ec_sensors_read,
>  	.write_raw = &cros_ec_sensors_write,
>  };
> @@ -195,11 +195,11 @@ static int cros_ec_sensors_probe(struct platform_device *pdev)
>  	if (!indio_dev)
>  		return -ENOMEM;
>  
> -	ret = cros_ec_sensors_core_init(pdev, indio_dev, true);
> +	ret = cros_ec_sensors_core_init(pdev, indio_dev, &ec_sensors_info,
> +					true);
>  	if (ret)
>  		return ret;
>  
> -	indio_dev->info = &ec_sensors_info;
>  	state = iio_priv(indio_dev);
>  	for (channel = state->channels, i = CROS_EC_SENSOR_X;
>  	     i < CROS_EC_SENSOR_MAX_AXIS; i++, channel++) {
> diff --git a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> index ac53ea32c1b1..08fb5d3dc7b5 100644
> --- a/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> +++ b/drivers/iio/common/cros_ec_sensors/cros_ec_sensors_core.c
> @@ -10,6 +10,7 @@
>  #include <linux/iio/buffer.h>
>  #include <linux/iio/common/cros_ec_sensors_core.h>
>  #include <linux/iio/iio.h>
> +#include <linux/iio/sysfs.h>
>  #include <linux/iio/kfifo_buf.h>
>  #include <linux/iio/trigger_consumer.h>
>  #include <linux/kernel.h>
> @@ -86,8 +87,42 @@ static int cros_ec_get_host_cmd_version_mask(struct cros_ec_device *ec_dev,
>  	return ret;
>  }
>  
> +/**
> + * cros_ec_sensors_read_freq() - sysfs function to get available frequencies
> + * @dev: Device structure for this device.
> + * @attr: Description of the attribute.
> + * @buf: Incoming string
> + *
> + * The later modes are only relevant to the ring buffer - and depend on current
> + * mode. Note that data sheet gives rather wide tolerances for these so integer
> + * division will give good enough answer and not all chips have them specified
> + * at all.
> + **/
> +static ssize_t cros_ec_sensors_read_freq(struct device *dev,
> +					 struct device_attribute *attr,
> +					 char *buf)
> +{
> +	struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> +	struct cros_ec_sensors_core_state *state = iio_priv(indio_dev);
> +
> +	return snprintf(buf, PAGE_SIZE, "[%d 1 %d]\n", state->min_freq,
> +			state->max_freq);
Whilst it is a bit more fiddly I would much prefer if this was done with
the info_mask_shared_by_all_available bit mask in the iio_dev and providing
the read_avail callback.

The original reason to introduce this form was as part of trying to
(far too slowly) kill off as much hand defined ABI as possible. 
Ultimate aim is to make the IIO interface optional for cases where
the channels are mostly being used by other consumer drivers rather than
being directly consumed by userspace.  To do that we need all of
these elements to be easily accessible from the consumer hooks.



> +}
> +
> +static IIO_DEV_ATTR_SAMP_FREQ_AVAIL(cros_ec_sensors_read_freq);
> +
> +static struct attribute *cros_ec_sensors_attributes[] = {
> +	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
> +	NULL,
> +};
> +
> +static const struct attribute_group cros_ec_sensors_attribute_group = {
> +	.attrs = cros_ec_sensors_attributes,
> +};
> +
>  int cros_ec_sensors_core_init(struct platform_device *pdev,
>  			      struct iio_dev *indio_dev,
> +			      struct iio_info *info,
>  			      bool physical_device)
>  {
>  	struct device *dev = &pdev->dev;
> @@ -149,6 +184,9 @@ int cros_ec_sensors_core_init(struct platform_device *pdev,
>  		}
>  	}
>  
> +	info->attrs = &cros_ec_sensors_attribute_group;
> +	indio_dev->info = info;
> +
>  	return 0;
>  }
>  EXPORT_SYMBOL_GPL(cros_ec_sensors_core_init);
> diff --git a/drivers/iio/light/cros_ec_light_prox.c b/drivers/iio/light/cros_ec_light_prox.c
> index 308ee6ff2e22..1772e339cf14 100644
> --- a/drivers/iio/light/cros_ec_light_prox.c
> +++ b/drivers/iio/light/cros_ec_light_prox.c
> @@ -161,7 +161,7 @@ static int cros_ec_light_prox_write(struct iio_dev *indio_dev,
>  	return ret;
>  }
>  
> -static const struct iio_info cros_ec_light_prox_info = {
> +static struct iio_info cros_ec_light_prox_info = {
>  	.read_raw = &cros_ec_light_prox_read,
>  	.write_raw = &cros_ec_light_prox_write,
>  };
> @@ -184,11 +184,11 @@ static int cros_ec_light_prox_probe(struct platform_device *pdev)
>  	if (!indio_dev)
>  		return -ENOMEM;
>  
> -	ret = cros_ec_sensors_core_init(pdev, indio_dev, true);
> +	ret = cros_ec_sensors_core_init(pdev, indio_dev,
> +					&cros_ec_light_prox_info, true);
>  	if (ret)
>  		return ret;
>  
> -	indio_dev->info = &cros_ec_light_prox_info;
>  	state = iio_priv(indio_dev);
>  	state->core.type = state->core.resp->info.type;
>  	state->core.loc = state->core.resp->info.location;
> diff --git a/drivers/iio/pressure/cros_ec_baro.c b/drivers/iio/pressure/cros_ec_baro.c
> index 034ce98d6e97..cd3be0f16226 100644
> --- a/drivers/iio/pressure/cros_ec_baro.c
> +++ b/drivers/iio/pressure/cros_ec_baro.c
> @@ -107,7 +107,7 @@ static int cros_ec_baro_write(struct iio_dev *indio_dev,
>  	return ret;
>  }
>  
> -static const struct iio_info cros_ec_baro_info = {
> +static struct iio_info cros_ec_baro_info = {
>  	.read_raw = &cros_ec_baro_read,
>  	.write_raw = &cros_ec_baro_write,
>  };
> @@ -130,11 +130,11 @@ static int cros_ec_baro_probe(struct platform_device *pdev)
>  	if (!indio_dev)
>  		return -ENOMEM;
>  
> -	ret = cros_ec_sensors_core_init(pdev, indio_dev, true);
> +	ret = cros_ec_sensors_core_init(pdev, indio_dev, &cros_ec_baro_info,
> +					true);
>  	if (ret)
>  		return ret;
>  
> -	indio_dev->info = &cros_ec_baro_info;
>  	state = iio_priv(indio_dev);
>  	state->core.type = state->core.resp->info.type;
>  	state->core.loc = state->core.resp->info.location;
> diff --git a/include/linux/iio/common/cros_ec_sensors_core.h b/include/linux/iio/common/cros_ec_sensors_core.h
> index 32fd08bbcf52..f170a72ac08d 100644
> --- a/include/linux/iio/common/cros_ec_sensors_core.h
> +++ b/include/linux/iio/common/cros_ec_sensors_core.h
> @@ -114,12 +114,14 @@ struct platform_device;
>   * cros_ec_sensors_core_init() - basic initialization of the core structure
>   * @pdev:		platform device created for the sensors
>   * @indio_dev:		iio device structure of the device
> + * @info:		iio info structure with read and write callback
>   * @physical_device:	true if the device refers to a physical device
>   *
>   * Return: 0 on success, -errno on failure.
>   */
>  int cros_ec_sensors_core_init(struct platform_device *pdev,
> -			      struct iio_dev *indio_dev, bool physical_device);
> +			      struct iio_dev *indio_dev, struct iio_info *info,
> +			      bool physical_device);
>  
>  /**
>   * cros_ec_sensors_capture() - the trigger handler function

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