On Thu, 5 Jan 2023, BALATON Zoltan wrote:
Hello,
I got reports from several users trying to run AmigaOS4 on sam460ex on Apple
silicon Macs that they get missing graphics that I can't reproduce on x86_64.
With help from the users who get the problem we've narrowed it down to the
following:
It looks like that data written to the sm501's ram in
qemu/hw/display/sm501.c::sm501_2d_operation() is then not seen from
sm501_update_display() in the same file. The sm501_2d_operation() function is
called when the guest accesses the emulated card so it may run in a different
thread than sm501_update_display() which is called by the ui backend but I'm
not sure how QEMU calls these. Is device code running in iothread and display
update in main thread? The problem is also independent of the display backend
and was reproduced with both -display cocoa and -display sdl.
We have confirmed it's not the pixman routines that sm501_2d_operation() uses
as the same issue is seen also with QEMU 4.x where pixman wasn't used and
with all versions up to 7.2 so it's also not some bisectable change in QEMU.
It also happens with --enable-debug so it doesn't seem to be related to
optimisation either and I don't get it on x86_64 but even x86_64 QEMU builds
run on Apple M1 with Rosetta 2 show the problem. It also only seems to affect
graphics written from sm501_2d_operation() which AmigaOS4 uses extensively
but other OSes don't and just render graphics with the vcpu which work
without problem also on the M1 Macs that show this problem with AmigaOS4.
Theoretically this could be some missing syncronisation which is something
ARM and PPC may need while x86 doesn't but I don't know if this is really the
reason and if so where and how to fix it). Any idea what may cause this and
what could be a fix to try?
Any idea anyone? At least some explanation if the above is plausible or if
there's an option to disable the iothread and run everyting in a single
thread to verify the theory could help. I've got reports from at least 3
people getting this problem but I can't do much to fix it without some
help.
(Info on how to run it is here:
http://zero.eik.bme.hu/~balaton/qemu/amiga/#amigaos
but AmigaOS4 is not freely distributable so it's a bit hard to reproduce.
Some Linux X servers that support sm501/sm502 may also use the card's 2d
engine but I don't know about any live CDs that readily run on sam460ex.)
Thank you,
BALATON Zoltan
