iio: magnetometer: Add driver for Yamaha YAS530

This adds an IIO magnetometer driver for the Yamaha
YAS530 family of magnetometer/compass chips YAS530,
YAS532 and YAS533.

A quick survey of the source code released by different
vendors reveal that we have these variants in the family
with some deployments listed:

 * YAS529 MS-3C (2005 Samsung Aries)
 * YAS530 MS-3E (2011 Samsung Galaxy S Advance)
 * YAS532 MS-3R (2011 Samsung Galaxy S4)
 * YAS533 MS-3F (Vivo 1633, 1707, V3, Y21L)
 * (YAS534 is a magnetic switch)
 * YAS535 MS-6C
 * YAS536 MS-3W
 * YAS537 MS-3T (2015 Samsung Galaxy S6, Note 5)
 * YAS539 MS-3S (2018 Samsung Galaxy A7 SM-A750FN)

The YAS529 is so significantly different from the
YAS53x variants that it will require its own driver.
The YAS537 and YAS539 have slightly different register
sets but have strong similarities so a common driver
patching this one will probably be reasonable.

The source code for Samsung Galaxy A7's YAS539 is not
that is significantly different from the YAS530 in the
Galaxy S Advance, so I believe we will only need this
one driver with quirks to handle all of them.

The YAS539 is actively announced on Yamaha's devices
site:
https://device.yamaha.com/en/lsi/products/e_compass/

This is a driver written from scratch using buffered
IIO and runtime PM handling regulators and reset.

Thanks to Andy Shevchenko for great help in finding all
the special kernel infrastructure functions and quirks
during review of this driver.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: phone-devel@vger.kernel.org
Cc: Jonathan Bakker <xc-racer2@live.ca>
Link: https://lore.kernel.org/r/20201224120820.1120099-2-linus.walleij@linaro.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/magnetometer/Kconfig

@@ -205,4 +205,19 @@ config SENSORS_RM3100_SPI
 	  To compile this driver as a module, choose M here: the module
 	  will be called rm3100-spi.
 
+config YAMAHA_YAS530
+	tristate "Yamaha YAS530 family of 3-Axis Magnetometers (I2C)"
+	depends on I2C
+	select REGMAP_I2C
+	select IIO_BUFFER
+	select IIO_TRIGGERED_BUFFER
+	help
+	  Say Y here to add support for the Yamaha YAS530 series of
+	  3-Axis Magnetometers. Right now YAS530, YAS532 and YAS533 are
+	  fully supported.
+
+	  This driver can also be compiled as a module.
+	  To compile this driver as a module, choose M here: the module
+	  will be called yamaha-yas.
+
 endmenu

drivers/iio/magnetometer/Makefile

@@ -28,3 +28,5 @@ obj-$(CONFIG_SENSORS_HMC5843_SPI)	+= hmc5843_spi.o
 obj-$(CONFIG_SENSORS_RM3100)		+= rm3100-core.o
 obj-$(CONFIG_SENSORS_RM3100_I2C)	+= rm3100-i2c.o
 obj-$(CONFIG_SENSORS_RM3100_SPI)	+= rm3100-spi.o
+
+obj-$(CONFIG_YAMAHA_YAS530)		+= yamaha-yas530.o