Re: [BUG] PDC20268 crashing during DMA setup on stock Debian 2.6.12-1-powerpc

[Kyle Moffett <mrmacman_g4@mac.com>]

On Oct 19, 2005, at 21:36:44, Benjamin Herrenschmidt wrote:

> Kyle Moffett wrote:
>
> > 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().

This is verified by adding printks to the code.  This is exactly  
where it crashes.


> > 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.

With heavy printk debugging, I have identified that the hwif->mmio is  
getting set to 2 somewhere (even though the PDC driver never touches  
it).  I added an extra line in the PDC init code to explicitly zero  
hwif->mmio, but I get the same result, so something else is mashing  
on the PDC hwif.


> 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 ?

This is the only possibility that I can think of, but I'm having a  
hard time getting enough lines of pre-BUG output.  Is there any way  
to turn off the BUG() lines and just show the printks before that point?

Cheers,
Kyle Moffett


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