video: backlight: mt6370: Add MediaTek MT6370 support

MediaTek MT6370 is a SubPMIC consisting of a single cell battery charger
with ADC monitoring, RGB LEDs, dual channel flashlight, WLED backlight
driver, display bias voltage supply, one general purpose LDO, and the
USB Type-C & PD controller complies with the latest USB Type-C and PD
standards.

Add support for the MediaTek MT6370 backlight driver.
It controls 4 channels of 8 series WLEDs in
2048 (only for MT6370/MT6371) / 16384 (only for MT6372)
current steps (30 mA) in exponential or linear mapping curves.
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: ChiaEn Wu <chiaen_wu@richtek.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220830034042.9354-11-peterwu.pub@gmail.com

drivers/video/backlight/Kconfig

@@ -268,6 +268,19 @@ config BACKLIGHT_MAX8925
 	  If you have a LCD backlight connected to the WLED output of MAX8925
 	  WLED output, say Y here to enable this driver.
 
+config BACKLIGHT_MT6370
+	tristate "MediaTek MT6370 Backlight Driver"
+	depends on MFD_MT6370
+	help
+	  This enables support for Mediatek MT6370 Backlight driver.
+	  It's commonly used to drive the display WLED. There are 4 channels
+	  inside, and each channel supports up to 30mA of current capability
+	  with 2048 current steps (only for MT6370/MT6371) or 16384 current
+	  steps (only for MT6372) in exponential or linear mapping curves.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called "mt6370-backlight".
+
 config BACKLIGHT_APPLE
 	tristate "Apple Backlight Driver"
 	depends on X86 && ACPI

drivers/video/backlight/Makefile

@@ -44,6 +44,7 @@ obj-$(CONFIG_BACKLIGHT_LP855X)		+= lp855x_bl.o
 obj-$(CONFIG_BACKLIGHT_LP8788)		+= lp8788_bl.o
 obj-$(CONFIG_BACKLIGHT_LV5207LP)	+= lv5207lp.o
 obj-$(CONFIG_BACKLIGHT_MAX8925)		+= max8925_bl.o
+obj-$(CONFIG_BACKLIGHT_MT6370)		+= mt6370-backlight.o
 obj-$(CONFIG_BACKLIGHT_OMAP1)		+= omap1_bl.o
 obj-$(CONFIG_BACKLIGHT_PANDORA)		+= pandora_bl.o
 obj-$(CONFIG_BACKLIGHT_PCF50633)	+= pcf50633-backlight.o