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Date: Wed, 5 Feb 2003 18:38:08 +0100
From: Stephan von Krawczynski <skraw@ithnet.com>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: rossb@google.com, alan@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: 2.4.21-pre4: PDC ide driver problems with shared interrupts
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On 05 Feb 2003 18:34:55 +0100
Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Wed, 2003-02-05 at 18:19, Ross Biro wrote:
> > Benjamin Herrenschmidt wrote:
> > 
> > >While I agree with you here, I don't think it's what's happening.
> > >	/* clear INTR & ERROR flags */
> > >	hwif->OUTB(dma_stat|6, hwif->dma_status);
> > >
> > >  
> > >
> > You have way to much faith in the hardware.  Promise is especially known 
> > for not keeping to the spec.  I wouldn't trust the interrupt bit to be 
> > valid unless a dma is actually active, i.e. that
> > 
> >                   hwif->OUTB(hwif->INB(dma_base)|1, dma_base);
> > 
> > has actually been written.  
> > 
> > I've actually had a manufacturer tell me that they don't worry about the 
> > spec, just making things work with Windows.
> 
> Ok, so that gives us 2 possibilities. The above problem, which would be
> fixed by locking all around ide_dma_read/write (or rather in the
> _caller_, seems better so we don't have to drop the lock for ATAPI).
> 
> And a possible wraparound of waiting_for_dma if 255 IRQs come in from
> whatever device we share the IRQ line with.
> 
> I beleive both need fixing...
> 
> Ben.

Ok, yet another small brick in the wall: this mb has 64bit/66MHz PCI slots. PDC
is only 32bit/33MHz PCI. So it may well be that others are in fact _able_ to
produce a damn lot more data/interrupts than the PDC. I am pretty astonished by
the number of interrupts created by the 3com tg3 cards anyways...

-- 
Regards,
Stephan
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