[maemo-developers] [maemo-developers] Re: backlight

[From: Arnaud Patard (Rtp)]

Frantisek Dufka <dufkaf at seznam.cz> writes:

> I hope the darkest level won't be too bright either. I see darker
> level when writing 1 via sysfs then it is possible via gui. When
> writing 2 it is same level as possible with GUI. But when writing 2
> via sysfs it immediatelly returns 1 on read (and the brightness is
> same). I'll try the ioctl too. Thank you.

It's not too bright imho. If you want to test I've uploaded the source I
used for testing here : http://rtpnet.nerim.net/n770/test.c
Take care of not setting something more than 0x7f.

>
> Frantisek
>
> Arnaud Patard (Rtp) wrote:
>> 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