[coreboot] Getting an WXGA+ LED MVA panel to work on T400: "G141C1-L01"

[Merlin Büge]

Hello everyone!


This is my first post to this mailing list :)


I'm trying to get a specific panel working on my Thinkpad T400 which runs
libreboot. It's an WXGA+ MVA panel (CMO G141C1-L01) and I have soldered an
adapter cable for it. From what I have found, nobody succeeded on this mod yet -
there are some attempts on 51nb.com, but only for the T410. I basically took
some already existing adapter cable, and modified a few pins, so that it would
match up exactly with the datasheets. I used the LG LP141WP2-TLB1 for reference.
Some details about my adapter cable can be found here:

http://forum.thinkpads.com/viewtopic.php?f=45&t=121151

In the first post there are also links to the datasheets of the two panels in
question.

Of course I thoroughly checked all my self-made connections and modifications,
but only with some general purpose DMM for continuity. They all seem fine.


So far backlight + PWM control works, but I have no image displayed, both in
libreboot (with GRUB2 as payload) and Linux (up-to-date Arch Linux).

I tried the panel both with the latest stock ROM (3.23/EC 1.06) and with
the latest libreboot release, which is currently 2016090
(t400_8mb_usqwerty_vesafb.rom in my case).

Since I have not much experience with such low-level hardware stuff, could
someone maybe help me with this or direct me to some useful direction, how I
can debug this?

I already tried booting with i915.lvds_channel_mode=2 (since I was not able
to figure out what mode was actually used, because this module parameter is
normally set to "0", which means the channel mode is taken from BIOS).

I attached the EDIDs of both panels, the coreboot log (cbmem -c) of both
panels, and a kernel log of both panels. I also attached a kernel log of the
MVA panel with drm debbuging enabled (drm.debug=0x1e log_buf_len=1M). Note that
all of the logs were taken from the T400 with the latest libreboot release.
It would be great if somebody could have a look at it. (I don't understand much
of it.)

Here is a picture of the adapter cable, so that you have an idea what it looks
like: https://lut.im/funPftuHF0/3sndAspbdiwOpTN4.jpg


I already put *a lot* of effort in this project, and I would be very happy if it
succeeded at the end of the day. I would design some PCBs then, so that this
would basically become a drop-in replacement. Background is: The T400 is a very
desirable target for libreboot, since it's build on the latest Intel hardware
currently supported in libreboot for laptops. And (not only in the libreboot
community) it is sadly well known for its rather bad TN panels. Also, it would
be something that I could give back to the libreboot community.

Since I have not much experience with mailing lists, please correct my of any
'bad' behavior.

Thank you for reading this,
and for any advice in advance :)


Regards,

Merlin





-- 
Merlin Büge <toni at bluenox07.de>
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