iio: adc: Add TI ADS131M0x ADC driver

Add a new IIO ADC driver for Texas Instruments ADS131M0x devices
(ADS131M02/03/04/06/08). These are 24-bit, up to 64 kSPS, simultaneous-
sampling delta-sigma ADCs accessed via SPI.

Highlights:
- Supports 2/3/4/6/8-channel variants with per-channel RAW and SCALE.
- Implements device-required full-duplex fixed-frame transfers.
- Handles both input and output CRC

Note: Despite the almost identical name, this hardware is not
compatible with the ADS131E0x series handled by
drivers/iio/adc/ti-ads131e08.c.

Signed-off-by: David Jander <david@protonic.nl>
Co-developed-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Author: yope

drivers/iio/adc/Kconfig

@@ -1722,6 +1722,17 @@ config TI_ADS131E08
 	  This driver can also be built as a module. If so, the module will be
 	  called ti-ads131e08.
 
+config TI_ADS131M02
+	tristate "Texas Instruments ADS131M02"
+	depends on SPI && REGULATOR
+	select CRC_ITU_T
+	help
+	  Say yes here to get support for Texas Instruments ADS131M02, ADS131M03,
+	  ADS131M04, ADS131M06 and ADS131M08 chips.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called ti-ads131m02.
+
 config TI_ADS7138
 	tristate "Texas Instruments ADS7128 and ADS7138 ADC driver"
 	depends on I2C

drivers/iio/adc/Makefile

@@ -150,6 +150,7 @@ obj-$(CONFIG_TI_ADS1119) += ti-ads1119.o
 obj-$(CONFIG_TI_ADS124S08) += ti-ads124s08.o
 obj-$(CONFIG_TI_ADS1298) += ti-ads1298.o
 obj-$(CONFIG_TI_ADS131E08) += ti-ads131e08.o
+obj-$(CONFIG_TI_ADS131M02) += ti-ads131m02.o
 obj-$(CONFIG_TI_ADS7138) += ti-ads7138.o
 obj-$(CONFIG_TI_ADS7924) += ti-ads7924.o
 obj-$(CONFIG_TI_ADS7950) += ti-ads7950.o