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

[Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>]

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? :/

Notes:
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.


ATB,

Mark.