Backlight Control Issues

[Chris Quartier]

Hi,

I'm porting Android 2.2 (linux kernel 2.6.32) onto an omap with other
custom hardware, and I'm having problems with Android controlling the
backlight for my LCD screen. In the kernel, I have used the generic
backlight driver, which creates sysfs nodes at "/sys/class/backlight/
my-bl/" and I can properly change the backlight brightness and power
from those nodes (echo [0 - 255] > /sys/class/backlight/my-bl/
brightness). In order for Android to change the backlight I saw that I
must create the liblights library. I've done that, and liblights
points at the correct sysfs nodes. The problem is, when I go to
Settings->Display->Brightness in Android, the slider does not do
anything. The screen off timeout also seems to have no effect - my LCD
stays on forever.

I have tried adding log prints into my liblights library but never see
any of them happen. From what I gather, there is a Lights Service that
calls into my liblights library. In the logcat output I see where the
SystemServer is starting the Lights Service, but I get no clue in any
other logs about what is happening with that service. I can see in the
logcat events buffer that something is happening when I change the
brightness slider.

As for the screen timeout, I do have power management disabled
(setprop hw.nopm true) in my init.rc file because currently it breaks
things. Will the screen timeout not work without power management?

Is there something I am missing? I feel like I am running in circles
with this.

[Chris Quartier]

I figured out my problems. It is a naming convention issue for the
shared library.

In hardware/libhardware/hardware.c, I noticed the call hw_get_module
looks for various sets of names for the hardware modules. If you
follow the porting guide from here: http://source.android.com/porting/lights.html
it says to name your library liblights.so. Well, that appears to be
misleading information. I had to name my lights library "lights.
($ro.board.platform).so" - the hardware module id ends up being the
first part (lights), and you can use one of 4 different system
properties for the 2nd name (in my case I used the system prop
ro.board.platform). The only other possibility is to name your lights
library "lights.default.so" Another caveat is to place this shared
library in /system/lib/hw and not in /system/lib. The hardware.c
implementation is hard-coded to look there.

Once I got the naming and location right, Android was finally able to
latch into my backlight and control it. I still have some minor
problems but they may be coding issues that I will iron out as I
continue testing.

Hope this helps anyone else with similar problems...