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SubjectRe: [BUG] PDC20268 crashing during DMA setup on stock Debian 2.6.12-1-powerpc
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> BusMaster-DMA definitely should be enabled on that card. After a lot
> of looking through icky IDE code, I've determined that the reason for
> the crash is that if there is a "mate", or another IDE bus on the
> same card, then hwif->dma_master is set to hwif->mate->dma_base on
> the secondary channel. Since DMA explicitly wasn't enabled on the
> primary channel, hwif->dma_master on the secondary is 0 even though
> dma is enabled, and therefore we hit that BUG().
>
> Therefore it seems that the only issue is ide_get_or_set_dma_base is
> returning 0 when it should return a valid DMA base. In that
> function, the only ways that function can even theoretically return 0
> without printing any weird error messages is "if (hwif->mmio)" or "if
> (hwif->mate && hwif->mate->dma_base)". The latter can't happen
> before hwif->mate is set up (since the problem is while initializing
> the primary). Could hwif->mmio be nonzero somehow? The only drivers
> that seem to set it are pci/sgiioc4, pci/siimage, ppc/pmac, and a
> couple misc arch drivers.
>
> I see a couple theoretical possibilities:
> * hwif->mate and hwif->mate->dma_base are set for the primary
> while still initializing it (before any secondary is set up.
> * hwif->mmio is set somehow even though it shouldn't be, is the
> value ever pre-initialized to 0?

Maybe there is some fighting going on between ppc/pmac.c and that driver
over the hwif's and you end up with mmio inadvertently set ?

> > Again, best is you pour printk's all over setup-pci.c and ide-dma.c
> > to figure out what's going on...
>
> I wish I could but the machine is remote and in-production, so it's
> hard to have time to do much with it. I'm trying as best I can to
> walk through the sources by hand, specifically with regards to
> changes between the two. I'm hoping I can come up with a good enough
> guess by Thanksgiving, so that when I have a week near the server to
> test things out I can make significant progress.


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