Change in coreboot[master]: console: Allow VPD to disable an otherwise enabled coreboot console

[Patrick Georgi (Code Review)]

Patrick Georgi has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/45208 )

Change subject: console: Allow VPD to disable an otherwise enabled coreboot console
......................................................................

Patch Set 4:

(1 comment)

Patchset:

PS4: 
Since this is coming back to my agenda, I intend to revive this patch in some shape or form.

Background: For some things we want to do in automated testing in CrOS we need access to a live feed of what happens during boot.

One option would be to use the image.serial.bin that we create in the Chrome OS firmware build process and switch between the two images. Big downside: We'd test a very different binary (instead of a binary with a few different flags, as we customarily do), which brings test validity issues and also process difficulties (we'd have to keep image.serial.bin around in lots of places where we don't ship it today)

Another option is to have the serial code present but normally disabled. So VPD is a bad place to put the toggle, got it.

As for Marc's proposal to use the get_console_loglevel() mechanism: The idea isn't to reduce verbosity, it's about having all log data end up in cbmem at all times, but have serial used only occasionally, but with the above properties.

GBB might be an easier sell wrt overhead brought into the bootblock (GBB support code is already compiled for the bootblock and liberally used across vboot), so that's something I'd be prepared to implement. That's still a relatively Chrome OS specific solution though, even if I can put most of the GBB wrangling into vboot and keep just a hook in the generic code.

Thoughts?