ps2: Fix issue #501 and #502

[Volker Rümelin]

Since commit ff6e1624b3 (pckbd: don't update OBF flags if
KBD_STAT_OBF is set) the OSes Minoca OS and Visopsys no longer
have a working PS/2 keyboard and mouse. This is caused by a
PS/2 queue stall due to a lost interrupt in the guest OS. This
already happened before commit ff6e1624b3, but no one noticed
because up to that point QEMU sent gratuitous keyboard and mouse
interrupts and the queue restarted with keyboard input or mouse
movement.

The lost interrupt is a guest bug. The fact that it's always
lost is due to an inexact PS/2 keyboard emulation. The way in
which the two operating systems e.g. set the keyboard LEDs,
leaves a keyboard ACK reply in the keyboard queue that is
unexpected for the guests.

This patch series improves the PS/2 keyboard emulation.

There's a workaround for issue #501 and #502 so I don't think
this is rc3 material. But that decision is up to the maintainers.

To verify patch 2/3 I plugged in an additional PS/2 keyboard
into the host and started Linux with the command line option
initcall_blacklist=i8042_init. Here is an example of the sequence
to set the keyboard LEDs.

# #regular sequence to set the keyboard LEDs
# inb --hex 0x64
1c
# #PS/2 queue is empty
# outb 0x60 0xed
# inb --hex 0x64
15
# inb --hex 0x60
fa
# inb --hex 0x64
14
# outb 0x60 0x01
# inb --hex 0x64
15
# inb --hex 0x60
fa
# inb --hex 0x64
14

# #alternative sequence to set the keyboard LEDs
# inb --hex 0x64
14
# outb 0x60 0xed
# outb 0x60 0x01
# inb --hex 0x64
15
# inb --hex 0x60
fa
# inb --hex 0x64
14

Volker Rümelin (3):
  ps2: use the whole ps2 buffer but keep queue size
  ps2: use a separate keyboard command reply queue
  ps2: migration support for command reply queue

 hw/input/ps2.c | 214 ++++++++++++++++++++++++++++++-------------------
 1 file changed, 133 insertions(+), 81 deletions(-)

--
2.26.2