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

[Avi Kivity <avi@redhat.com>]

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
>> accesses.
>>
>> Using these stubs, however, distinguishes PCI device DMA transactions 
>> from
>> 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 
>> time.
>>
>> That is, it allows us to update individual PCI drivers to support an 
>> IOMMU
>> without having yet determined the details of how the IOMMU emulation 
>> will
>> operate.  This will let us remove the most bitrot-sensitive part of an
>> IOMMU patch in advance.
>>
>> Signed-off-by: David Gibson<david@gibson.dropbear.id.au>
>
> 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.

-- 
error compiling committee.c: too many arguments to function