[Gta04-owner] Linux 3.2-rc2 on GTA04

[Dr. H. Nikolaus Schaller]

Am 24.11.2011 um 21:53 schrieb NeilBrown:

> On Thu, 24 Nov 2011 21:16:56 +0100 Johannes Schauer <j.schauer at email.de>
> wrote:
> 
>> Hi,
>> 
>> On Wed, Nov 23, 2011 at 06:42:38AM +1100, NeilBrown wrote:
>>> I don't even have a display plugged in - just the bare board with a
>>> paperclip to hold the battery in place, and the serial and USB cables
>>> plugged in.
>>> 
>>> As far as I can see, the backlight control code I have is exactly what is in
>>> the 3.1 'master' branch of the goldelico git tree.
>>> 
>>> It contains:
>>> 
>>> 	gpio_set_value(57, 0); //shutdown backlight first
>>> 
>>> in gta04_init() in arch/arm/mach-omap2/board-omap3gta04.c
>>> 
>>> The hw-validation kernel doesn't have that line.  You could try removing it
>>> and see what happens.
>>> It was added by commit 8d109e588b840c288ea1ad4d8f166080510be55a with minimal
>>> explanation.
>> 
>> There is no difference after removing that line.
>> 
>> Additionally, the backlight only turns off once xorg is starting. Before
>> the backlight is on and shows the penguin.
>> 
>> Is there something in /sys that I can use to control the backlight?
> 
> The gpio line can be controlled from
>   /sys/class/gpio/gpio57
> 
> cd /sys/class/gpio/gpio57
> echo 1 > value
> 
> however I suspect you will find that '1' is already the value.
> 
> I didn't change any of this code from the code David had, except that I
> replaced the base kernel:-)
> So presumably there is some change in common code that is messing things up.
> 
> The particular pin/ball/pad which GPIO57 comes out of can be multiplexed
> between 5 functions - the other important one being gpt_11_pwm_evt which can
> be pulse-width-modulated to get brightness levels.
> The default is gpmc_ncs6  which I think might be a General Purpose Memory
> Controller Chip Select line... In any case I cannot find where the multiplex
> is told to switch that line to gpio57.

Pinmux selection is done in U-Boot (unless there is additional code in the
kernel).

Are you sure that the backlight really turns off? Or does the
framebuffer turn completely black? In that case you see some
light glowing. If you remove the battery, there should be a
noticeable change.

BR,
Nikolaus