On Mon, 2017-03-06 at 13:46 -0600, Larry Finger wrote:
> I was able to create a PPC emulation with debian-8.7.1-powerpc-CD-1.iso
> > following the instructions in https://gmplib.org/~tege/qemu.html. My only
> problem was that "-net tap" fails and I did not find any way to get
> networking
> working.
>
> After looking at the screen through a number of crashes, I have determined
> that
> the top entry in the traceback comes from dmam_alloc_coherent(). I have not
> been
> able to see the offset to determine which BUG_ON call in that routine is
> being
> triggered.
>
> I tried to modify panic() to see if I could keep the screen on longer after
> the
> failure, but no joy so far.
I think the problem is this code in drivers/macintosh/macio_asic.c:
#ifdef CONFIG_PCI
/* Set the DMA ops to the ones from the PCI device, this could be
* fishy if we didn't know that on PowerMac it's always direct ops
* or iommu ops that will work fine
*
* To get all the fields, copy all archdata
*/
dev->ofdev.dev.archdata = chip->lbus.pdev->dev.archdata;
#endif /* CONFIG_PCI */
This is definitely bad. A quick fix is to copy the new dev->dma_ops field
(as well, there is still stuff in archdata that we need too).
A better long term fix is to have a set of macio_dma_ops wrappers that do
"the right thing".
Cheers,
Ben.
