[Gta04-owner] Linux 3.2-rc2 on GTA04

NeilBrown neilb at suse.de
Thu Nov 24 21:53:17 CET 2011


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.

I hope to look at this in more detail later today so look forward to a more
complete answer in some hours.

NeilBrown



> 
> cheers, josch
> _______________________________________________
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> Gta04-owner at goldelico.com
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