On 11 May 2013 06:09, liu ping fan <qemul...@gmail.com> wrote: > On Wed, May 8, 2013 at 2:30 AM, Peter Maydell <peter.mayd...@linaro.org> > wrote: >> Also, technically speaking get_system_memory() is never the >> right answer, though in practice it's good enough for our >> purposes. (returning get_system_memory() would allow a bus >> master DMA device to access back into the PCI bus by >> DMAing to the address in system memory where the PCI host >> controller is mapped, which I'm guessing is not possible >> on real hardware.) >> > I think although it is rare case, but PCI device can fetch another's > data on its pci-ram, expecially pci-spec does not forbid it.
Yes, certainly, but this happens because the other pci device is present in the PCI address space, not because PCI device A talks to the host controller's CPU-facing interface and accesses PCI device B that way... -- PMM
