[coreboot-gerrit] Change in coreboot[master]: nb/x4x: Disable IGD when external GPU is found

[Arthur Heymans (Code Review)]

Arthur Heymans has posted comments on this change. ( https://review.coreboot.org/18504 )

Change subject: nb/x4x: Disable IGD when external GPU is found
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Patch Set 14:

> Lenovo's Hybrid Driver is special, as it mimics a vendor bios
 > feature and you've got a hardware switch to connect the panel to
 > one of the GPUs.
 > In theory reverse prime should work, but in my opinion the option
 > ROM will be run on igd, as it's connected to the panel, and that
 > would make it decode VGA cycles/Primary.

I have only tested this setup to be 'working' (but useless in linux) without option rom. I'm not if SeaBIOS has some special rules for running VGA options roms but I'd think running IGD option rom while not decoding VGA would cause problems instead of switching back VGA decode cycles to it? (quickly going through eaglelake option disassembly makes me think option does not though that GGC bit1, but I'll try to test it)

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Gerrit-MessageType: comment
Gerrit-Change-Id: I74890918feb0f1ff6b971c4aaa96f1f7b75266ac
Gerrit-PatchSet: 14
Gerrit-Project: coreboot
Gerrit-Branch: master
Gerrit-Owner: Arthur Heymans <arthur at aheymans.xyz>
Gerrit-Reviewer: Arthur Heymans <arthur at aheymans.xyz>
Gerrit-Reviewer: Kyösti Mälkki <kyosti.malkki at gmail.com>
Gerrit-Reviewer: Nico Huber <nico.h at gmx.de>
Gerrit-Reviewer: Patrick Rudolph <siro at das-labor.org>
Gerrit-Reviewer: Paul Menzel <paulepanter at users.sourceforge.net>
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