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Date: Fri, 6 Dec 2002 18:36:09 +0000
From: Matthew Wilcox <willy@debian.org>
To: "David S. Miller" <davem@redhat.com>
Cc: adam@yggdrasil.com, James.Bottomley@steeleye.com,
       linux-kernel@vger.kernel.org, willy@debian.org
Subject: Re: [RFC] generic device DMA implementation
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References: <200212061619.IAA22144@baldur.yggdrasil.com> <20021206.101715.113691767.davem@redhat.com>
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On Fri, Dec 06, 2002 at 10:17:15AM -0800, David S. Miller wrote:
> Specifically, it took years to get most developers confortable with
> pci_alloc_consitent() and friends.  I totally fear that asking them to
> now add cache flushing stuff to their drivers takes the complexity way
> over the edge.
> 
> Willy, these PCXS/T processors sound like a newer cpu, do you mean to
> tell me the caches are totally not coherent with device bus space?
> 
> Please elaborate, I want to learn more.

Nono, these are _old_ machines, probably stopped production round about
1995 or so.  We mentioned these briefly back in the original days of
the pci_alloc_consistent interface discussions.  These machines cannot
allocate uncached memory, nor can the peripherals snoop the CPU's cache
(or vice versa).  As I indicated to Adam, there's a fairly limited range
of devices available for these systems and there shouldn't be a huge
problem converting the few drivers we need to these interfaces.

-- 
"It's not Hollywood.  War is real, war is primarily not about defeat or
victory, it is about death.  I've seen thousands and thousands of dead bodies.
Do you think I want to have an academic debate on this subject?" -- Robert Fisk
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