[coreboot-gerrit] Change in coreboot[master]: lib: Add a mutex

[Raul Rangel (Code Review)]

Attention is currently required from: Nico Huber, Xiang W, Philipp Hug, Jonathan Neuschäfer, Tim Wawrzynczak, Angel Pons, Kyösti Mälkki, Rob Barnes, Karthik Ramasubramanian.
Raul Rangel has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/59320 )

Change subject: lib: Add a mutex
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Patch Set 15:

(1 comment)

Patchset:

PS15:
> You can have your size comparison of the two approaches, but for that I need a commit hash for Raul' […]

DMA performance doesn't depend on UART or log level. Each DMA transaction takes anywhere from 8-10ms, so we don't need to poll it constantly. As for numbers, the rest of the patch train has them.

I can rework the patch train sometime next week.