Hello,
I just tried to compile my own kernel with backlight changes and found this:
- my kernel works in the device without any ill effects and without
messing with initfs, great :) I used kernel from
http://repository.maemo.org/pool/maemo1.1/free/k/kernel-source-2.6.12.3/
I removed translation from 0-15 to 0-127 so backlight_max returns 127
now and any value goes directly to tahvo backlight. UI works still the
same. It still has 9 levels going from same minimum to same maximum only
values in sysfs are scaled now. It means that either UI dynamically
adjusts itself to the value of sysfs backlight_max or it uses directly
tahvo. I hope the first one is true. Now I am trying to make translation
table in kernel and keep 16 levels but let each one to be configured
with value 0-127. Second soulution is trying to hack brigtness applet to
provide more levels than 9. I'll probably try both solutions.
Frantisek
Arnaud Patard (Rtp) wrote:
Brad Midgley <[EMAIL PROTECTED]> writes:
Arnaud
The strange thing is that when you're on the lowest level the gui will
allow (1), the display goes a little dimmer than that when idle and the
sys file actually reports the value 0. But if you *write* a 0 to the sys
file, the backlight turns off altogether.
This leaves two interpretations for a 0 value.
after looking at the kernel sources, you have 2 ways of setting the PWM
value for the backlight :
- through sysfs
- through /dev/tavho with an ioctl (look at the tahvo-user.c and tahvo.h
files in the kernel).
If you use the first method, you're have to cope with a scale factor eg
when you write 1, you'll write 1*0x7f/0x0f=0x08. This is also happening
when you read the file.
If you use the second method, you may write an arbitrary value for the
pwm. This is probably how is working the gui. This is why 1 with the gui
is not the same 1 as with sysfs.
If you try to set the level with the ioctl, to something like 1, you'll
get a darker screen as expected but it'll go a few sec later to the gui
setting.
I hope that this helps you :)
Arnaud
Brad
Looks like it can be controlled via ioctl on the framebuffer device.
http://maemo.org/lxr/source/osso-af-utils/src/omapfb.h
struct lcd_panel has pointer
int (*set_bklight_level)(struct lcd_panel *panel,unsigned int level);
I'll try to figure out how it can be called. If anyone knows, don't
hesitate to answer :)
well, you can call it by echoing to
/sys/bus/platform/devices/omapfb/panel/backlight_level
In reality, the function called is lph8923_panel_set_bklight_level() in
lcd_lph8923.c (which in turn calls tahvo_set_backlight_level). The code
is saying that 1 is the lowest value (except 0 :P) and 15 the highest.
So, you can't go lower unless there's an other way to play with the
level.
Arnaud
Frantisek
Brad Midgley wrote:
Frantisek
I noticed this too, but we know it can go lower... the backlight goes
just a bit lower when you're idle and before it turns off altogether.
Brad
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