'comconsole_pcidev'. The former allows to set the base address of the
serial console i/o port. The later takes the string of the format
'bus:device:function:[bar]' as a value and uses the serial port attached
as PCI device at the specified location for console.
Both variants pass 'hw.uart.console' variable to the uart driver to
properly hand-over the kernel console.
Change allows to use ISA serial ports other than COM1 for the
loader/kernel console without loader recompilation. Also, you can use
PCI-attached port as the console, e.g. Intel AMT serial pseudo-port on
some motherboards based on Q67 chipset.
Reviewed by: jhb
MFC after: 2 weeks
b462104206