driver -> ../../../bus/platform/drivers/msm_fb
In the kernel source I see the following:
# CONFIG_FB_MSM_BACKLIGHT is not set CONFIG_BACKLIGHT_LCD_SUPPORT=y CONFIG_BACKLIGHT_CLASS_DEVICE=y
config BACKLIGHT_LP855X tristate "Backlight driver for TI LP855X" depends on BACKLIGHT_CLASS_DEVICE && I2C help This supports TI LP8550, LP8551, LP8552, LP8553 and LP8556 backlight driver.
What am I missing here? IM-A870K_defconfig attached.
I am looking at this because the backlight minimum level is way too bright. Haking system framework apk or using gravitybox to lower the minium brightness doesn't help - 20 seems to be the kernel limit in how low the brightness can go down. Values of 7-19 doesn't differ from 20, and values less than 7 turns off the backlight entirely. There is probably a constant minimum defined in the driver which is probably not exposed to sysfs control because there doesn't seem to have a register file for the minimum backlight current.
Edit: Several menu item in drivers/video/backlight/Kconfig has default value of y
config BACKLIGHT_GENERIC tristate "Generic (aka Sharp Corgi) Backlight Driver" default y help Say y to enable the generic platform backlight driver previously known as the Corgi backlight driver. If you have a Sharp Zaurus SL-C7xx, SL-Cxx00 or SL-6000x say y. config BACKLIGHT_LOCOMO tristate "Sharp LOCOMO LCD/Backlight Driver" depends on SHARP_LOCOMO default y help If you have a Sharp Zaurus SL-5500 (Collie) or SL-5600 (Poodle) say y to enable the LCD/backlight driver. config BACKLIGHT_OMAP1 tristate "OMAP1 PWL-based LCD Backlight" depends on ARCH_OMAP1 default y help This driver controls the LCD backlight level and power for the PWL module of OMAP1 processors. Say Y if your board uses this hardware. config BACKLIGHT_HP680 tristate "HP Jornada 680 Backlight Driver" depends on SH_HP6XX default y help If you have a HP Jornada 680, say y to enable the backlight driver. config BACKLIGHT_HP700 tristate "HP Jornada 700 series Backlight Driver" depends on SA1100_JORNADA720_SSP && !PREEMPT default y help If you have an HP Jornada 700 series, say Y to include backlight control driver.
It looks like msm_fb.C and msm_fb_bl.C in drivers/video/msm/ gives the generic sysfs interface to control lcd backlight brightness, but I still am unable to figure out the actual driver for the backlight driver chip used.