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Re: [Qemu-devel] PATCH/RFC: PCI memory mapping

From: Brian Wheeler
Subject: Re: [Qemu-devel] PATCH/RFC: PCI memory mapping
Date: Fri, 03 Apr 2009 11:05:49 -0400

On Thu, 2009-04-02 at 22:40 +0000, Paul Brook wrote:
> On Thursday 02 April 2009, Brian Wheeler wrote:
> > [first off, if there's an easier way to do this, let me know!]
> >
> > This patch adds an address mapping function to the PCI bus so the host
> > chipset can remap PCI generated addresses to the appropriate physical
> > addresses.
> This should be integrated with the DMA APIs.  Individual devices must not 
> need 
> to be aware of bus bridges. All remapping should be handled by the DMA 
> routines.  In principle there's no reason for this to be specific to PCI. 
> SPARC machines already have an IOMMU, so you should make sure your solution 
> also covers those systems.
> I recommend looking back in the list archives, there have been several 
> discussions about the requirements for bus address mapping.
> Paul

I've been looking around the archives and I'm not finding what I'm
looking for...though it may be that words like dma, address, etc are
terribly generic in this context.  I've found a few promising patches in
the archives, but they don't seem to be in the code.

Here's the problem I'm trying to solve:  The alpha has an IOMMU which
translates pci addresses to addresses which are used by the system.  The
first mapping is for local connect addresses which work out to:
   (0x80000000000ULL | (bus * 0x200000000ULL) | address

Another mapping uses scatter-gather.  A third one uses a direct connect
mapping which is a base/range => new address mapping.

My question is:  where/how do I hook my function to translate the
address from cpu_physical_memory_{register,read,write}() as called by
the different devices into the addresses that I need?

So, for example, a cirrus vga device on bus 1 when calling:

cpu_register_physical_memory(addr, s->vram_size,

The address actually gets mapped to the alpha's address
0x80200000000 + addr?

How do other architectures do this?  Looking around the source, I'm not
finding anything that stands out....

Thanks, and sorry for the newbie questions!

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