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    SubjectRe: [PATCH V2] VFIO driver: Non-privileged user level PCI drivers
    On Thu, Jul 01, 2010 at 09:29:04AM -0600, Alex Williamson wrote:
    > On Tue, 2010-06-08 at 14:21 -0700, Tom Lyon wrote:
    > > +The VFIO_DMA_MASK ioctl is used to set the maximum permissible DMA address
    > > +(device dependent). It takes a single unsigned 64 bit integer as an argument.
    > > +This call also has the side effect of enabling PCI bus mastership.
    > Hi Tom,
    > This interface doesn't make sense for the MAP_IOVA user. Especially in
    > qemu, we have no idea what the DMA mask is for the device we're
    > assigning. It doesn't really matter though because the guest will use
    > bounce buffers internally once it loads the device specific drivers and
    > discovers the DMA mask. This only seems relevant if we're using a
    > DMA_MAP call that gets to pick the dmaaddr, so I'd propose we only make
    > this a required call for that interface, and create a separate ioctl for
    > actually enabling bus master. Thanks,
    > Alex

    I expect there's no need for a separate ioctl to do this:
    you can do this by write to the control register.


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