iio: adc: ad7173: add calibration support

The ad7173 family of chips has up to four calibration modes.

Internal zero scale: removes ADC core offset errors.
Internal full scale: removes ADC core gain errors.
System zero scale: reduces offset error to the order of channel noise.
System full scale: reduces gain error to the order of channel noise.

All voltage channels will undergo an internal zero/full scale
calibration at bootup.

System zero/full scale can be done after bootup using the newly created
iio interface 'sys_calibration' and 'sys_calibration_mode'

Signed-off-by: Guillaume Ranquet <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jonathan Cameron <[e-mail]>

drivers/iio/adc/ad7173.c

···
 #define AD7173_FILTER_ODR0_MASK		GENMASK(5, 0)
 #define AD7173_MAX_CONFIGS		8
 
+#define AD7173_MODE_CAL_INT_ZERO		0x4 /* Internal Zero-Scale Calibration */
+#define AD7173_MODE_CAL_INT_FULL		0x5 /* Internal Full-Scale Calibration */
+#define AD7173_MODE_CAL_SYS_ZERO		0x6 /* System Zero-Scale Calibration */
+#define AD7173_MODE_CAL_SYS_FULL		0x7 /* System Full-Scale Calibration */
+
 struct ad7173_device_info {
 	const unsigned int *sinc5_data_rates;
 	unsigned int num_sinc5_data_rates;
···
 	bool has_input_buf;
 	bool has_int_ref;
 	bool has_ref2;
+	bool has_internal_fs_calibration;
 	bool higher_gpio_bits;
 	u8 num_gpios;
 };
···
 struct ad7173_channel {
 	unsigned int ain;
 	struct ad7173_channel_config cfg;
+	u8 syscalib_mode;
 };
 
 struct ad7173_state {
···
 	.has_input_buf = true,
 	.has_current_inputs = true,
 	.has_int_ref = true,
+	.has_internal_fs_calibration = true,
 	.clock = 2 * HZ_PER_MHZ,
 	.sinc5_data_rates = ad7173_sinc5_data_rates,
 	.num_sinc5_data_rates = ARRAY_SIZE(ad7173_sinc5_data_rates),
···
 	.has_input_buf = true,
 	.has_current_inputs = true,
 	.has_int_ref = true,
+	.has_internal_fs_calibration = true,
 	.clock = 2 * HZ_PER_MHZ,
 	.sinc5_data_rates = ad7173_sinc5_data_rates,
 	.num_sinc5_data_rates = ARRAY_SIZE(ad7173_sinc5_data_rates),
···
 	.has_temp = true,
 	.has_input_buf = true,
 	.has_int_ref = true,
+	.has_internal_fs_calibration = true,
 	.clock = 2 * HZ_PER_MHZ,
 	.sinc5_data_rates = ad7173_sinc5_data_rates,
 	.num_sinc5_data_rates = ARRAY_SIZE(ad7173_sinc5_data_rates),
···
 	.has_temp = true,
 	.has_input_buf = true,
 	.has_int_ref = true,
+	.has_internal_fs_calibration = true,
 	.clock = 8 * HZ_PER_MHZ,
 	.sinc5_data_rates = ad4115_sinc5_data_rates,
 	.num_sinc5_data_rates = ARRAY_SIZE(ad4115_sinc5_data_rates),
···
 	.has_temp = true,
 	.has_input_buf = true,
 	.has_int_ref = true,
+	.has_internal_fs_calibration = true,
 	.clock = 4 * HZ_PER_MHZ,
 	.sinc5_data_rates = ad4116_sinc5_data_rates,
 	.num_sinc5_data_rates = ARRAY_SIZE(ad4116_sinc5_data_rates),
···
 	.wr_table = &ad7173_access_table,
 	.read_flag_mask = BIT(6),
 };
+
+enum {
+	AD7173_SYSCALIB_ZERO_SCALE,
+	AD7173_SYSCALIB_FULL_SCALE,
+};
+
+static const char * const ad7173_syscalib_modes[] = {
+	[AD7173_SYSCALIB_ZERO_SCALE] = "zero_scale",
+	[AD7173_SYSCALIB_FULL_SCALE] = "full_scale",
+};
+
+static int ad7173_set_syscalib_mode(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan,
+				    unsigned int mode)
+{
+	struct ad7173_state *st = iio_priv(indio_dev);
+
+	st->channels[chan->channel].syscalib_mode = mode;
+
+	return 0;
+}
+
+static int ad7173_get_syscalib_mode(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan)
+{
+	struct ad7173_state *st = iio_priv(indio_dev);
+
+	return st->channels[chan->channel].syscalib_mode;
+}
+
+static ssize_t ad7173_write_syscalib(struct iio_dev *indio_dev,
+				     uintptr_t private,
+				     const struct iio_chan_spec *chan,
+				     const char *buf, size_t len)
+{
+	struct ad7173_state *st = iio_priv(indio_dev);
+	bool sys_calib;
+	int ret, mode;
+
+	ret = kstrtobool(buf, &sys_calib);
+	if (ret)
+		return ret;
+
+	mode = st->channels[chan->channel].syscalib_mode;
+	if (sys_calib) {
+		if (mode == AD7173_SYSCALIB_ZERO_SCALE)
+			ret = ad_sd_calibrate(&st->sd, AD7173_MODE_CAL_SYS_ZERO,
+					      chan->address);
+		else
+			ret = ad_sd_calibrate(&st->sd, AD7173_MODE_CAL_SYS_FULL,
+					      chan->address);
+	}
+
+	return ret ? : len;
+}
+
+static const struct iio_enum ad7173_syscalib_mode_enum = {
+	.items = ad7173_syscalib_modes,
+	.num_items = ARRAY_SIZE(ad7173_syscalib_modes),
+	.set = ad7173_set_syscalib_mode,
+	.get = ad7173_get_syscalib_mode
+};
+
+static const struct iio_chan_spec_ext_info ad7173_calibsys_ext_info[] = {
+	{
+		.name = "sys_calibration",
+		.write = ad7173_write_syscalib,
+		.shared = IIO_SEPARATE,
+	},
+	IIO_ENUM("sys_calibration_mode", IIO_SEPARATE,
+		 &ad7173_syscalib_mode_enum),
+	IIO_ENUM_AVAILABLE("sys_calibration_mode", IIO_SHARED_BY_TYPE,
+			   &ad7173_syscalib_mode_enum),
+	{ }
+};
+
+static int ad7173_calibrate_all(struct ad7173_state *st, struct iio_dev *indio_dev)
+{
+	int ret;
+	int i;
+
+	for (i = 0; i < st->num_channels; i++) {
+		if (indio_dev->channels[i].type != IIO_VOLTAGE)
+			continue;
+
+		ret = ad_sd_calibrate(&st->sd, AD7173_MODE_CAL_INT_ZERO, st->channels[i].ain);
+		if (ret < 0)
+			return ret;
+
+		if (st->info->has_internal_fs_calibration) {
+			ret = ad_sd_calibrate(&st->sd, AD7173_MODE_CAL_INT_FULL,
+					      st->channels[i].ain);
+			if (ret < 0)
+				return ret;
+		}
+	}
+
+	return 0;
+}
 
 static int ad7173_mask_xlate(struct gpio_regmap *gpio, unsigned int base,
 			     unsigned int offset, unsigned int *reg,
···
 	if (!st->config_cnts)
 		return -ENOMEM;
 
+	ret = ad7173_calibrate_all(st, indio_dev);
+	if (ret)
+		return ret;
+
 	/* All channels are enabled by default after a reset */
 	return ad7173_disable_all(&st->sd);
 }
···
 		.storagebits = 32,
 		.endianness = IIO_BE,
 	},
+	.ext_info = ad7173_calibsys_ext_info,
 };
 
 static const struct iio_chan_spec ad7173_temp_iio_channel_template = {