T420: Legacy VGA display and external monitor issue
When an external monitor is connected (docking station 4337 + DVI), the boot up screen is shown on both monitors (SeaBios Text output).
With "highres framebuffer" selected, this works perfectly, also with the Ubuntu password screen for disk encryption.
(The original bios did not initialize the external monitor at all).
However, when building with legacy VGA mode, the following issue was observed:
* The bootup screen is only shown correctly on the EXTERNAL monitor
* The INTERNAL display shows a completely distorted image (colors, position shifted,...)
-> You cannot even use the display when Linux is booted, you can only work with the external monitor.
-> You have to reboot WITHOUT the external monitor connected, and plug it in afterwards.
Or: use highres framebuffer, as I mentioned. Nevertheless there might be situations when you want to use legacy VGA.
* at least provide an option to disable all external monitors at boot, so that they can be initialized later by the OS (this was the behavior the original bios of the T420 showed).