Figuring out the driver used for lcd-backlight
On my device vega a870k,
the lcd backlight control sysfs driver points to
driver -> ../../../bus/platform/drivers/msm_fb
doesn't seem to be useful in figuring out what exactly is being used for the driver. Unlike the led controls which point to
giving me hints that the driver should be something like pm8xxx
In the kernel source I see the following:
# CONFIG_FB_MSM_BACKLIGHT is not set
there are tons of menu config items, such as
tristate "Backlight driver for TI LP855X"
depends on BACKLIGHT_CLASS_DEVICE && I2C
This supports TI LP8550, LP8551, LP8552, LP8553 and LP8556
Now, I suppose the relevant building instruction should be contained in IM-A870K_defconfig. However, I find no references in building for any 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
tristate "Generic (aka Sharp Corgi) Backlight Driver"
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.
tristate "Sharp LOCOMO LCD/Backlight Driver"
depends on SHARP_LOCOMO
If you have a Sharp Zaurus SL-5500 (Collie) or SL-5600 (Poodle) say y to
enable the LCD/backlight driver.
tristate "OMAP1 PWL-based LCD Backlight"
depends on ARCH_OMAP1
This driver controls the LCD backlight level and power for
the PWL module of OMAP1 processors. Say Y if your board
uses this hardware.
tristate "HP Jornada 680 Backlight Driver"
depends on SH_HP6XX
If you have a HP Jornada 680, say y to enable the
tristate "HP Jornada 700 series Backlight Driver"
depends on SA1100_JORNADA720_SSP && !PREEMPT
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.