Re: [PATCH] set altix preferred console

["Bjorn Helgaas" <bjorn.helgaas@hp.com>]

> Our prom currently does not build up ACPI tables describing PCI (or any
> IO)
> devices.  We are working toward that goal, but it is still
> work in progress and will be some time yet before this is done.
>
> It is because of this shortcoming that we have to rely on the PCDP table
> to provide the io addresses needed for VGA console.
>
> Outside of PCDP, our earliest opportunity to get information about VGA
> devices is through the call sequence initiated with
> subsys_initcall(sn_pci_init), which would seem way too late for early boot
> messages.

It's the same for us.  We don't find out about our built-in serial
ports until the 8250 driver initializes, which is pretty late.  So
we have "8250_early" that uses information from the PCDP to talk
to the serial port before the normal 8250 driver discovers it.
The important thing is that the PCDP doesn't influence the naming
of the device (and there isn't really a "name" for VGA devices,
AFAIK).

> Out of curiousity, what are the mmio_tra/ioport_tra fields in the PCDP PCI
> interface structure intended for if not for this purpose?

You *can* use the _tra fields in the PCDP -- that's what they're
there for.  But the PCDP should be *optional*, and I think it's
not for your current setup.

If we don't build pcdp.o on an HP box, the console still works
just fine; it just doesn't work until the 8250 driver discovers
the port, which is fairly late.

So I think all you need to do is add some SN-specific code
somewhere that discovers the VGA device.  It sounds like the
only way to do that right now is to get the information from
the PCDP, so I guess that's what you need to do.  But having
this duplicated in the SN code means that you won't need the
change to pcdp.c.