Re: [PATCH 1/5] iio: hmc5843: Add attribute for available measurement config

[Jonathan Cameron <jic23@kernel.org>]

On 07/02/16 22:21, Cristina Moraru wrote:
> Add static attribute meas_conf_available to show available
> configurations for the bias current.
> 
> API for setting bias measurement configuration:
> 
> 0 - Normal measurement configuration (default): In normal measurement
>     configuration the device follows normal measurement flow. Pins BP
>     and BN are left floating and high impedance.
> 
> 1 - Positive bias configuration: In positive bias configuration, a
>     positive current is forced across the resistive load on pins BP
>     and BN.
> 
> 2 - Negative bias configuration. In negative bias configuration, a
>     negative current is forced across the resistive load on pins BP
>     and BN.
> 
> 3 - Only available on HMC5983. Magnetic sensor is disabled.
>     Temperature sensor is enabled.
> 
> Signed-off-by: Cristina Moraru <cristina.moraru09@gmail.com>
I'd much prefer to see this done using the iio_enum magic, giving
something like.

cat meas_conf_available 
normal, positivebias, negativebias, disabled

then have meas_conf read as one of these strings and take one as a write.

This abi is never going to make all that much sense to someone who
hasn't read the datasheet / docs, but if possible it is nice to
give them a hint by using informative strings as the values.

Jonathan
> ---
>  drivers/staging/iio/magnetometer/hmc5843_core.c | 83 +++++++++++++++++++------
>  1 file changed, 65 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/staging/iio/magnetometer/hmc5843_core.c b/drivers/staging/iio/magnetometer/hmc5843_core.c
> index 4aab022..4e2a7ec 100644
> --- a/drivers/staging/iio/magnetometer/hmc5843_core.c
> +++ b/drivers/staging/iio/magnetometer/hmc5843_core.c
> @@ -66,6 +66,34 @@
>  #define HMC5843_MEAS_CONF_NEGATIVE_BIAS		0x02
>  #define HMC5843_MEAS_CONF_MASK			0x03
>  
> +/*
> + * API for setting the measurement configuration to
> + * Normal, Positive bias and Negative bias
> + *
> + * From the datasheet:
> + * 0 - Normal measurement configuration (default): In normal measurement
> + *     configuration the device follows normal measurement flow. Pins BP
> + *     and BN are left floating and high impedance.
> + *
> + * 1 - Positive bias configuration: In positive bias configuration, a
> + *     positive current is forced across the resistive load on pins BP
> + *     and BN.
> + *
> + * 2 - Negative bias configuration. In negative bias configuration, a
> + *     negative current is forced across the resistive load on pins BP
> + *     and BN.
> + *
> + * 3 - Only available on HMC5983. Magnetic sensor is disabled.
> + *     Temperature sensor is enabled.
> + */
> +static const int hmc5843_regval_to_meas_conf[] = {
> +	0, 1, 2
> +};
> +
> +static const int hmc5983_regval_to_meas_conf[] = {
> +	0, 1, 2, 3
> +};
> +
>  /* Scaling factors: 10000000/Gain */
>  static const int hmc5843_regval_to_nanoscale[] = {
>  	6173, 7692, 10309, 12821, 18868, 21739, 25641, 35714
> @@ -109,6 +137,8 @@ static const int hmc5983_regval_to_samp_freq[][2] = {
>  /* Describe chip variants */
>  struct hmc5843_chip_info {
>  	const struct iio_chan_spec *channels;
> +	const int *regval_to_meas_conf;
> +	const int n_regval_to_meas_conf;
>  	const int (*regval_to_samp_freq)[2];
>  	const int n_regval_to_samp_freq;
>  	const int *regval_to_nanoscale;
> @@ -174,24 +204,6 @@ static int hmc5843_read_measurement(struct hmc5843_data *data,
>  	return IIO_VAL_INT;
>  }
>  
> -/*
> - * API for setting the measurement configuration to
> - * Normal, Positive bias and Negative bias
> - *
> - * From the datasheet:
> - * 0 - Normal measurement configuration (default): In normal measurement
> - *     configuration the device follows normal measurement flow. Pins BP
> - *     and BN are left floating and high impedance.
> - *
> - * 1 - Positive bias configuration: In positive bias configuration, a
> - *     positive current is forced across the resistive load on pins BP
> - *     and BN.
> - *
> - * 2 - Negative bias configuration. In negative bias configuration, a
> - *     negative current is forced across the resistive load on pins BP
> - *     and BN.
> - *
> - */
>  static int hmc5843_set_meas_conf(struct hmc5843_data *data, u8 meas_conf)
>  {
>  	int ret;
> @@ -248,6 +260,28 @@ static IIO_DEVICE_ATTR(meas_conf,
>  			hmc5843_set_measurement_configuration,
>  			0);
>  
> +static ssize_t hmc5843_show_meas_conf_avail(struct device *dev,
> +					    struct device_attribute *attr,
> +					    char *buf)
> +{
> +	struct hmc5843_data *data = iio_priv(dev_to_iio_dev(dev));
> +
> +	size_t len = 0;
> +	int i;
> +
> +	for (i = 0; i < data->variant->n_regval_to_meas_conf; i++)
> +		len += scnprintf(buf + len, PAGE_SIZE - len,
> +			"%d ", data->variant->regval_to_meas_conf[i]);
> +
> +	/* replace trailing space by newline */
> +	buf[len - 1] = '\n';
> +
> +	return len;
> +}
> +
> +static IIO_DEVICE_ATTR(meas_conf_available, S_IRUGO,
> +	hmc5843_show_meas_conf_avail, NULL, 0);
> +
>  static
>  ssize_t hmc5843_show_samp_freq_avail(struct device *dev,
>  				     struct device_attribute *attr, char *buf)
> @@ -478,6 +512,7 @@ static const struct iio_chan_spec hmc5883_channels[] = {
>  
>  static struct attribute *hmc5843_attributes[] = {
>  	&iio_dev_attr_meas_conf.dev_attr.attr,
> +	&iio_dev_attr_meas_conf_available.dev_attr.attr,
>  	&iio_dev_attr_scale_available.dev_attr.attr,
>  	&iio_dev_attr_sampling_frequency_available.dev_attr.attr,
>  	NULL
> @@ -490,6 +525,9 @@ static const struct attribute_group hmc5843_group = {
>  static const struct hmc5843_chip_info hmc5843_chip_info_tbl[] = {
>  	[HMC5843_ID] = {
>  		.channels = hmc5843_channels,
> +		.regval_to_meas_conf = hmc5843_regval_to_meas_conf,
> +		.n_regval_to_meas_conf =
> +				ARRAY_SIZE(hmc5843_regval_to_meas_conf),
>  		.regval_to_samp_freq = hmc5843_regval_to_samp_freq,
>  		.n_regval_to_samp_freq =
>  				ARRAY_SIZE(hmc5843_regval_to_samp_freq),
> @@ -499,6 +537,9 @@ static const struct hmc5843_chip_info hmc5843_chip_info_tbl[] = {
>  	},
>  	[HMC5883_ID] = {
>  		.channels = hmc5883_channels,
> +		.regval_to_meas_conf = hmc5843_regval_to_meas_conf,
> +		.n_regval_to_meas_conf =
> +				ARRAY_SIZE(hmc5843_regval_to_meas_conf),
>  		.regval_to_samp_freq = hmc5883_regval_to_samp_freq,
>  		.n_regval_to_samp_freq =
>  				ARRAY_SIZE(hmc5883_regval_to_samp_freq),
> @@ -508,6 +549,9 @@ static const struct hmc5843_chip_info hmc5843_chip_info_tbl[] = {
>  	},
>  	[HMC5883L_ID] = {
>  		.channels = hmc5883_channels,
> +		.regval_to_meas_conf = hmc5843_regval_to_meas_conf,
> +		.n_regval_to_meas_conf =
> +				ARRAY_SIZE(hmc5843_regval_to_meas_conf),
>  		.regval_to_samp_freq = hmc5883_regval_to_samp_freq,
>  		.n_regval_to_samp_freq =
>  				ARRAY_SIZE(hmc5883_regval_to_samp_freq),
> @@ -517,6 +561,9 @@ static const struct hmc5843_chip_info hmc5843_chip_info_tbl[] = {
>  	},
>  	[HMC5983_ID] = {
>  		.channels = hmc5883_channels,
> +		.regval_to_meas_conf = hmc5983_regval_to_meas_conf,
> +		.n_regval_to_meas_conf =
> +				ARRAY_SIZE(hmc5983_regval_to_meas_conf),
>  		.regval_to_samp_freq = hmc5983_regval_to_samp_freq,
>  		.n_regval_to_samp_freq =
>  				ARRAY_SIZE(hmc5983_regval_to_samp_freq),
>