what do you mean "coreboot driver"? libgfxinit?
Yes, that's what's being used. The first logo looks full sized and the "press enter" message is on the actual bottom of the screen. Then tianocore boots and the logo is the same size but tianocore interface is just slightly bigger. It's all centered in my screen in a 600x600ish square.
Why would you do that? You can use upstream Tianocore master as-is by simply selecting the Uefipayload option.
To check for fixes. I thought the 2 options were coreboot_fb and uefipayloadpkg both from the mrchromebox repo. Tianocore master has 3k more commits than those. I figured out how to try it though and switched to upstream/master... same problem just missing the logo, etc. Does it run at a fixed size or something without scaling?
I'm only 5 days into this so I can for sure be wrong.