[Gta04-owner] Linux 3.2-rc2 on GTA04

NeilBrown neilb at suse.de
Thu Nov 24 22:29:48 CET 2011


On Thu, 24 Nov 2011 21:57:04 +0100 "Dr. H. Nikolaus Schaller"
<hns at goldelico.com> wrote:

> 
> 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).

Of course - that makes sense.  And now that I know where to look it is easy
to find.

> 
> 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.

The original report said that shining a bright torch the display made the
image just visible, so it wasn't blank, just no backlight.
Very strange.

NeilBrown
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