gpio: Add driver for Maxim MAX3191x industrial serializer

The driver was developed for and tested with the MAX31913 built into
the Revolution Pi by KUNBUS, but should work with all members of the
MAX3191x family:

MAX31910: low power
MAX31911: LED drivers
MAX31912: LED drivers + 2nd voltage monitor + low power
MAX31913: LED drivers + 2nd voltage monitor
MAX31953: LED drivers + 2nd voltage monitor + isolation
MAX31963: LED drivers + 2nd voltage monitor + isolation + buck regulator

Cc: Mathias Duckeck <m.duckeck@kunbus.de>
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/gpio/Kconfig

@@ -1255,6 +1255,16 @@ config GPIO_74X164
 	  shift registers. This driver can be used to provide access
 	  to more gpio outputs.
 
+config GPIO_MAX3191X
+	tristate "Maxim MAX3191x industrial serializer"
+	select CRC8
+	help
+	  GPIO driver for Maxim MAX31910, MAX31911, MAX31912, MAX31913,
+	  MAX31953 and MAX31963 industrial serializer, a daisy-chainable
+	  chip to make 8 digital 24V inputs available via SPI.  Supports
+	  CRC checksums to guard against electromagnetic interference,
+	  as well as undervoltage and overtemperature detection.
+
 config GPIO_MAX7301
 	tristate "Maxim MAX7301 GPIO expander"
 	select GPIO_MAX730X

drivers/gpio/Makefile

@@ -69,6 +69,7 @@ obj-$(CONFIG_ARCH_LPC32XX)	+= gpio-lpc32xx.o
 obj-$(CONFIG_GPIO_LP873X)	+= gpio-lp873x.o
 obj-$(CONFIG_GPIO_LP87565)	+= gpio-lp87565.o
 obj-$(CONFIG_GPIO_LYNXPOINT)	+= gpio-lynxpoint.o
+obj-$(CONFIG_GPIO_MAX3191X)	+= gpio-max3191x.o
 obj-$(CONFIG_GPIO_MAX730X)	+= gpio-max730x.o
 obj-$(CONFIG_GPIO_MAX7300)	+= gpio-max7300.o
 obj-$(CONFIG_GPIO_MAX7301)	+= gpio-max7301.o