[OpenBIOS] [PATCH 0/5] Enable bus master support for rtl8139 network cards on Apple PPC machines

Mark Cave-Ayland mark.cave-ayland at ilande.co.uk
Sun Aug 7 15:45:48 CEST 2016

On 05/08/16 21:44, BALATON Zoltan wrote:

>> Following up from this, I found out today that the reason OS 9 rtl8139
>> drivers don't work in QEMU is due to the same issue, i.e. by default
>> Apple OF appears to enable bus mastering upon boot (OpenBIOS currently
>> doesn't) and so many driver authors forget to explicitly enable this.
>> So taking this patch and making a few minor tweaks I was able to get the
>> rtl8139 working in OS 9.2 and surf the web in Classilla :)  I'm not sure
>> whether it solves similar issues people were having in 10.4.11 but I'd
>> invite people to test and report back.
> I'm not sure if this is the correct fix but I've found it before this
> was needed to get RTL8139 working.
> Recently I've seen changes in QEMU to calling realize functions for some
> devices that were not realized due to not being connected via a bridge
> and that mentioned that bus master is set on realize and this was needed
> to fix that (or something similar, not sure I got it completely and I've
> forgot it since; I think these were around commit 685f9a3 on QEMU). I've
> hoped this might also fix this issue but haven't tested that yet.
> Also on real hardware there's a bridge chip which is currently disabled
> due to OpenBIOS not handling it correctly according to a comment in
> uninorth.c.
> I'm not sure any of this is related to this issue, just mentioning it in
> case it rings a bell for someone.

AFAICT the bus mastering part is still needed since in QEMU the bus
master memory region (which is aliased onto system memory) is disabled
unless the bus master bit is set. It's fairly easy to spot this in the
monitor with "info mtree".

My interpretation of this is that any PCI device in QEMU which wishes to
read/write from system memory which isn't mapped via a BAR must also
have the bus master bit set. I'm not a PCI expert so someone feel free
to provide a more correct explanation :)



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