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Re: [Qemu-ppc] [Qemu-devel] [PULL 075/118] macio: handle non-block ATAPI

From: Mark Cave-Ayland
Subject: Re: [Qemu-ppc] [Qemu-devel] [PULL 075/118] macio: handle non-block ATAPI DMA transfers
Date: Wed, 25 Jun 2014 21:17:56 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:24.0) Gecko/20100101 Icedove/24.5.0

On 24/06/14 11:53, BALATON Zoltan wrote:

All I can say is that debugging this stuff isn't easy, particularly
with MorphOS which has some rather unusual behaviours. But what we
really need from you now over the next few days is for you to compare
the debug output between the working and non-working cases and figure
out if we can fix this in time for the 2.1 release. You have
everything you need (including my acceptance test of booting both
MorphOS and Darwin ISOs), so time to take a deep breath and begin what
should be a challenging yet ultimately rewarding debugging process :)

I'm still working on finding a solution for the exception problems with
OpenBIOS that prevent MorphOS from working and I failed to understand
the whole working of macio, DBDMA and the whole block layer so far but I
can try to debug it. Can you tell how to reproduce the problem with
Darwin? The Darwin images don't seem to work with -M mac99 either before
or after the patch so no regressions there.

It's fairly simple to reproduce here:

qemu-system-ppc -M g3beige -cdrom darwinppc-602.iso -boot d
qemu-system-ppc -M g3beige -cdrom darwinppc-801.iso -boot d
qemu-system-ppc -M mac99 -cdrom darwinppc-801.iso -boot d

For -M g3beige then darwinppc-602.iso tends to hang just after the "ADB present" line just before it finds the CDROM.

Rather annoyingly it seems to be a lot trickier to reproduce today than it was with my original tests, currently 1 in 8 boots compared to 1 in 3 when I did the OpenBIOS tests. Delays introduced by enabling debugging in pmac_ide_transfer() seem to make it easier to trigger, as does compiling with -O0 -g (slower) and also dropping the kernel FS cache.

Maybe it's an existing timing bug that happens to be exacerbated by the patch? :/

Darwin 6.02 doesn't support -M mac99 (always hangs) AFAICT.
Darwin 8.01 works but with -M mac99 IDE detection can take up to 30s or so.



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