staging: iio: adc: ad7192: Add system calibration support

This patch will add a system calibration attribute for each channel. Using
this option the user will have the ability to calibrate each channel for
zero scale and full scale. It uses the iio_chan_spec_ext_info and IIO_ENUM
to implement the functionality.
Signed-off-by: Mircea Caprioru <mircea.caprioru@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/ABI/testing/sysfs-bus-iio-adc-ad7192

@@ -13,3 +13,27 @@ Description:
 		need to minimize the system current consumption.
 		Reading gives the state of the bridge switch.
 		Writing '1' enables the bridge switch.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltagex_sys_calibration
+KernelVersion:
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Initiates the system calibration procedure. This is done on a
+		single channel at a time. Write '1' to start the calibration.
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltagex_sys_calibration_mode_available
+KernelVersion:
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Reading returns a list with the possible calibration modes.
+		There are two available options:
+		"zero_scale" - calibrate to zero scale
+		"full_scale" - calibrate to full scale
+
+What:		/sys/bus/iio/devices/iio:deviceX/in_voltagex_sys_calibration_mode
+KernelVersion:
+Contact:	linux-iio@vger.kernel.org
+Description:
+		Sets up the calibration mode used in the system calibration
+		procedure. Reading returns the current calibration mode.
+		Writing sets the system calibration mode.

drivers/staging/iio/adc/ad7192.c

@@ -155,6 +155,11 @@
  * The DOUT/RDY output must also be wired to an interrupt capable GPIO.
  */
 
+enum {
+   AD7192_SYSCALIB_ZERO_SCALE,
+   AD7192_SYSCALIB_FULL_SCALE,
+};
+
 struct ad7192_state {
 	struct regulator		*avdd;
 	struct regulator		*dvdd;
@@ -169,10 +174,80 @@ struct ad7192_state {
 	u8				devid;
 	u8				clock_sel;
 	struct mutex			lock;	/* protect sensor state */
+	u8				syscalib_mode[8];
 
 	struct ad_sigma_delta		sd;
 };
 
+static const char * const ad7192_syscalib_modes[] = {
+	[AD7192_SYSCALIB_ZERO_SCALE] = "zero_scale",
+	[AD7192_SYSCALIB_FULL_SCALE] = "full_scale",
+};
+
+static int ad7192_set_syscalib_mode(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan,
+				    unsigned int mode)
+{
+	struct ad7192_state *st = iio_priv(indio_dev);
+
+	st->syscalib_mode[chan->channel] = mode;
+
+	return 0;
+}
+
+static int ad7192_get_syscalib_mode(struct iio_dev *indio_dev,
+				    const struct iio_chan_spec *chan)
+{
+	struct ad7192_state *st = iio_priv(indio_dev);
+
+	return st->syscalib_mode[chan->channel];
+}
+
+static ssize_t ad7192_write_syscalib(struct iio_dev *indio_dev,
+				     uintptr_t private,
+				     const struct iio_chan_spec *chan,
+				     const char *buf, size_t len)
+{
+	struct ad7192_state *st = iio_priv(indio_dev);
+	bool sys_calib;
+	int ret, temp;
+
+	ret = strtobool(buf, &sys_calib);
+	if (ret)
+		return ret;
+
+	temp = st->syscalib_mode[chan->channel];
+	if (sys_calib) {
+		if (temp == AD7192_SYSCALIB_ZERO_SCALE)
+			ret = ad_sd_calibrate(&st->sd, AD7192_MODE_CAL_SYS_ZERO,
+					      chan->address);
+		else
+			ret = ad_sd_calibrate(&st->sd, AD7192_MODE_CAL_SYS_FULL,
+					      chan->address);
+	}
+
+	return ret ? ret : len;
+}
+
+static const struct iio_enum ad7192_syscalib_mode_enum = {
+	.items = ad7192_syscalib_modes,
+	.num_items = ARRAY_SIZE(ad7192_syscalib_modes),
+	.set = ad7192_set_syscalib_mode,
+	.get = ad7192_get_syscalib_mode
+};
+
+static const struct iio_chan_spec_ext_info ad7192_calibsys_ext_info[] = {
+	{
+		.name = "sys_calibration",
+		.write = ad7192_write_syscalib,
+		.shared = IIO_SEPARATE,
+	},
+	IIO_ENUM("sys_calibration_mode", IIO_SEPARATE,
+		 &ad7192_syscalib_mode_enum),
+	IIO_ENUM_AVAILABLE("sys_calibration_mode", &ad7192_syscalib_mode_enum),
+	{}
+};
+
 static struct ad7192_state *ad_sigma_delta_to_ad7192(struct ad_sigma_delta *sd)
 {
 	return container_of(sd, struct ad7192_state, sd);
@@ -770,9 +845,11 @@ static int ad7192_channels_config(struct iio_dev *indio_dev)
 		*chan = channels[i];
 		chan->info_mask_shared_by_all |=
 			BIT(IIO_CHAN_INFO_LOW_PASS_FILTER_3DB_FREQUENCY);
-		if (chan->type != IIO_TEMP)
+		if (chan->type != IIO_TEMP) {
 			chan->info_mask_shared_by_type_available |=
 				BIT(IIO_CHAN_INFO_SCALE);
+			chan->ext_info = ad7192_calibsys_ext_info;
+		}
 		chan++;
 	}