Currently, x86 firmware decides at coreboot bootblock time whether to enable the AP UART or not.

Enabling it costs power in suspend, so on MP firmware, the answer is "not".

Changing this setting currently requires deasserting WP and reflashing AP-RO.

It would be handy if this setting could be changed via crossystem, so that OS developers can get access to the AP UART via CCD without needing to deassert WP.