console: add support for QEMU's debugcon

Add support for sending debug output to an I/O port.

It can be used together with QEMU's isa-debugcon driver to log the
coreboot output to a file.  The port is configurable and defaults
to 0x402 which has established as the de facto standard. For example,
SeaBIOS+OVMF [1] use that one too.

    Open Virtual Machine Firmware
Change-Id: I0803f7fc70030242f80003e25c9449c37d71975e
Signed-off-by: Gerd Hoffmann <>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <>
Reviewed-by: Ronald G. Minnich <>
3 files changed