glamo backlight

Thomas White taw at
Sat Apr 10 17:37:31 CEST 2010

On Fri, 9 Apr 2010 12:43:10 +0200
mobi phil <mobi at> wrote:

> I am trying to use a kernel on 2.6.32 drm branch, but there are
> problems with the backlight. I got a "JBT not initialised!!" error
> blahblah.
> I looked into the driver code, and I see that theg jbt spi driver is
> not initialized. I think spi does not detect the jbt6k74 device,
> therefore it is not calling the driver init?
> fyi: /sys/bus/spi/devices does not list the jbt6k74 device... What
> could go wrong?

Hi - sorry for the late reply.  I'd marked your earlier email to reply
to, but never got round to it due to having a few other things to sort

The "JBT not initliased!!" error can safely be ignored.  It's a side
effect of a dirty hack I did to keep JBT and Glamo in sync when
switching modes - a simple function call and global device structure in
the JBT driver.  When the Glamo driver calls the JBT driver before the
JBT driver has been initialised, the JBT driver just skips over the
mode change.  This happens a couple of times during initialisation
before things get up and running.  That message should be ignored
and removed.

The correct full sysfs location for JBT should be:
/sys/bus/spi/devices/spi2.0/lcd/jbt6k74-lcd/ .  Getting the "not
initialised" message indicates that the correct code is compiled into
the kernel at least (the message is generated by the JBT driver, and
the Glamo driver won't compile without the JBT driver after my dirty
hack). If the device really doesn't exist, it'd be good to test with the
main 2.6.32 (non-KMS/DRM) branch (without trying to enable DRM in the
config, of course).  The 2.6.32-gdrm branch will not work with a non-KMS
configuration (i.e. normal glamo-fb compiled in) unless by sheer luck.
Main Openmoko 2.6.32 without DRM also still doesn't work, as far as I
know, but I could be slightly out of date there.

I've attached the config I currently use when compiling 2.6.32-gdrm.

Are you sure that the backlight is not coming on, rather than it being
on but the display being all black?  Neither the Glamo nor JBT driver
are actually responsible for the backlight coming on - the backlight
itself is "just" an LED-powering output from the PCF chip.  Is there
anything under /sys/class/backlight?


Thomas White <taw at>
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