Hi,

This RFC series attempt to fix a regression introduced in a4cb773928e,
and reported by Emilio:
http://lists.nongnu.org/archive/html/qemu-devel/2018-06/msg00317.html

Mark noticed the VGA and parallel I/O were overlapping:

(qemu) info mtree
address-space: memory
  0000000000000000-ffffffffffffffff (prio 0, i/o): system
    00000801fc000000-00000801fdffffff (prio 0, i/o): pci0-io
      ...
      00000801fc0003b4-00000801fc0003b5 (prio 0, i/o): vga
      00000801fc0003ba-00000801fc0003ba (prio 0, i/o): vga
      00000801fc0003bc-00000801fc0003c3 (prio 0, i/o): parallel
                                    ^^^                ^^^^^^^^
      00000801fc0003c0-00000801fc0003cf (prio 0, i/o): vga
                   ^^^
      00000801fc0003d4-00000801fc0003d5 (prio 0, i/o): vga
      00000801fc0003da-00000801fc0003da (prio 0, i/o): vga
      ...

In reset the parallel port is enabled. Since the emulated PALcode
directly accesses the VGA port without checking if the SIO parallel
port is enabled, I suppose the real PALcode does this check.

To avoid changing the emulated PALcode, a "parallel" property is used
to reset the SIO with the parallel device disabled.

I tried to implement the quickest simpler fix...

references used:
- http://www.osdever.net/FreeVGA/vga/portidx.htm
- https://retired.beyondlogic.org/spp/parallel.htm
- http://ww1.microchip.com/downloads/en/DeviceDoc/37c669.pdf
- linux/arch/alpha/kernel/smc37c669.c
- https://github.com/rth7680/qemu-palcode/blob/master/init.c#L290
- https://github.com/rth7680/qemu-palcode/blob/master/ioport.h#L48

Regards,

Phil.

Philippe Mathieu-Daudé (2):
  hw/isa/smc37c669-superio: Basic 'Config Registers' implementation
  hw/alpha/dp264: Disable the Super I/O parallel port

 hw/alpha/dp264.c           |  6 +++-
 hw/isa/smc37c669-superio.c | 73 +++++++++++++++++++++++++++++++++-----
 2 files changed, 70 insertions(+), 9 deletions(-)

-- 
2.17.1