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Re: [Qemu-devel] Re: PATCH, RFC: Generic DMA framework

From: Fabrice Bellard
Subject: Re: [Qemu-devel] Re: PATCH, RFC: Generic DMA framework
Date: Sun, 26 Aug 2007 13:30:40 +0200
User-agent: Thunderbird (X11/20070212)

Paul Brook wrote:
pci_gdma.diff: Convert PCI devices and targets

Any comments? The patches are a bit intrusive and I can't test the
targets except that they compile.
Shouldn't the PCI DMA object be a property of the PCI bus?
ie. we don't want/need to pass it round as a separate parameter. It can
be inferred form the device/bus.
I agree. Moreover the DMA is bus specific so I don't see a need to add a
generic DMA layer.

I can see use for a generic DMA interface. It has some nice possibilities for devices which can connect via a variety of busses and maybe for layering different busses within a system.

However I don't know how well this will work in practice for the machines qemu currently emulates.

I can see more uses for a simple bus interface which could be used at least for ISA devices. The API should include bus read/write functions (which can be used to implement DMA) and functions to allocate/free a memory region as we have for the CPU bus.

Of course the same must be added for PCI buses so that the PCI memory area can be mapped at any position in the CPU address space.


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