[coreboot] Hi-DPI displays and showing text information for kevin in depthcharge

[Paul Kocialkowski]

I am using upstream coreboot with top-of-tree depthcharge and vboot on
kevin (Chromebook Plus from Samsung) and I've patched depthcharge[0] to
display text messages instead of looking up bitmaps in the GBB/cbfs.

I noticed that corebootfb is using[1] a fixed 8x16 font for showing text
there. In addition, the RK3399 eDP code will always go with the
"recommended resolution" from the EDID, which is the highest one.

The result of this is that the displayed text looks really small on-
screen, which does not really provide a great user experience.

So I am wondering what the best way to solve this would be. I see a few
options:
* Having larger fonts for hi-dpi displays
* Scaling the font to reach a particular DPI (e.g. based on the physical
screen size reported from the EDID)
* Reducing the resolution, by optionally providing a preferred one from
the config

Among these, which ones do you think is the way to go? I think the
question is also whether we want a generic way to handle this or to do
it per-device (and also keep in mind that not every device has EDID
available, but may have a single hardcoded resolution, which could still
superseded by the suggested config option).

I like the idea of reducing the resolution. It may however also break
compatibility with e.g. ChromeOS that expects the framebuffer to be set
at the max resolution by coreboot.

[0]: http://git.code.paulk.fr/gitweb/?p=libettereboot.git;a=tree;f=projects/depthcharge/patches;h=dd17766e4b5217456f1d8ae20619a08bd34e9be4;hb=HEAD
[1]: https://review.coreboot.org/cgit/coreboot.git/tree/payloads/libpayload/drivers/video/corebootfb.c#n124

Cheers,

-- 
Paul Kocialkowski,

developer of free digital technology and hardware support.

Website: https://www.paulk.fr/
Coding blog: https://code.paulk.fr/
Git repositories: https://git.paulk.fr/ https://git.code.paulk.fr/
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