[coreboot] T400 screen issue / EDID handling

[Paul Menzel]

Dear Kroms,


Am Montag, den 13.07.2015, 09:43 +0200 schrieb kroms at posteo.be:

[…]

> > There are two more things two do.
> > 
> > 1. Contact the Linux i915 folks and ask them, if the module is able 
> > to detect the configuration itself and does not rely on the 
> > firmware or if there is a way to override that setting from the 
> > Linux command line.
> 
> Who is going to do this? Is this [1] the right community? I am not
> sure, if I am able to explain it right.
> If you want me to do this, what do you mean exactly with "the 
> module", is it "i915"?

Yes i915 and it’d be great if you could do it.

At least the second question should be answered. Looking at
`/sbin/modinfo i915` it shows that there is such an option already.

    parm:           lvds_channel_mode:Specify LVDS channel mode (0=probe BIOS [default], 1=single-channel, 2=dual-channel) (int)

So you could add `i915.lvds_channel_mode=2`, I think, to the Linux
command line and see if Linux is able to initialize your system.

> On [2], is written:
> "Linux (kernel) has its own init code (including EDID parsing). The
> current suspicion is that coreboot's own initialization code has 
> buggy EDID parsing in some way, such that the proper settings for the 
> panel are not used, leading to the failure."
> 
> Please tell me, if I understand it right:
> The kernel module should not rely on coreboot concerning the settings
> for the display and you want to know, 
> if the kernel module is able to get the needed information direct 
> from the display (EDID)? If this is possible, you want to know,
> if this is configurable with the Linux command line? Means "Linux 
> command line" the same as "kernel command line"?

Yes. But I am not sure if it’s related to EDID parsing at all. coreboot
just hard codes it.

> > 2. Improve coreboot so that the LVDS link configuration is detected
> > during runtime as the vendor firmware (VGA Option ROM/Video 
> > BIOS(?))
> > does.
> 
> While I am learning a lot of things working on this issue, this is 
> far above my skills.

No problem. Maybe somebody else will do it.


Thanks,

Paul


> [1] https://01.org/linuxgraphics/community/kernel
> [2] http://libreboot.org/docs/hcl/gm45_lcd.html
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