Re: [PATCH V2] VFIO driver: Non-privileged user level PCI drivers

["Michael S. Tsirkin" <mst@redhat.com>]

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.

-- 
MST