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Re: [Qemu-devel] [PATCH 01/10] Add stub functions for PCI device models

From: Anthony Liguori
Subject: Re: [Qemu-devel] [PATCH 01/10] Add stub functions for PCI device models to do PCI DMA
Date: Thu, 01 Sep 2011 11:05:48 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20110516 Lightning/1.0b2 Thunderbird/3.1.10

On 09/01/2011 11:03 AM, Avi Kivity wrote:
On 09/01/2011 06:55 PM, Anthony Liguori wrote:
On 09/01/2011 12:00 AM, David Gibson wrote:
This patch adds functions to pci.[ch] to perform PCI DMA operations. At
present, these are just stubs which perform directly cpu physical memory

Using these stubs, however, distinguishes PCI device DMA transactions
other accesses to physical memory, which will allow PCI IOMMU support to
be added in one place, rather than updating every PCI driver at that

That is, it allows us to update individual PCI drivers to support an
without having yet determined the details of how the IOMMU emulation
operate. This will let us remove the most bitrot-sensitive part of an
IOMMU patch in advance.

Signed-off-by: David Gibson<address@hidden>

I think this is the wrong approach given the introduction of the
memory API.

I think we should have a generic memory access function that takes a
MemoryRegion as it's first argument.

The PCI bus should then expose one memory region for each device
(that's how it can figure out where the access is coming from).

Richard/Avi, what do you think?

I think the patchset is fine. It routes all access through pci_dma_rw(),
which accepts a PCIDevice. We can later define pci_dma_rw() in terms of
the memory API and get the benefit of the memory hierarchy.

The challenge is what you do about something like ne2k where the core chipset can either be a PCI device or an ISA device. You would have to implement a wrapper around pci_dma_rw() in order to turn it into cpu_physical_memory_rw when doing ISA.


Anthony Liguori

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