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SubjectRe: virtio-pci new configuration proposal
On Wed, Nov 02, 2011 at 09:07:12PM +0200, Sasha Levin wrote:
> On Wed, 2011-11-02 at 21:08 +0200, Michael S. Tsirkin wrote:
> > On Wed, Nov 02, 2011 at 08:49:27PM +0200, Sasha Levin wrote:
> > > This is a proposal for a new layout of the virtio-pci config space.
> > >
> > > We will separate the current configuration into two: A virtio-pci common
> > > configuration and a device specific configuration. This allows more flexibility
> > > with adding features and makes usage easier, specifically in cases like the
> > > ones in virtio-net where device specific configurations depend on device
> > > specific features.
> > >
> > > The preferred location of the configuration will be a MMIO BAR, therefore
> > > several size optimizations such as the queue selector which were useful
> > > on a PIO BAR were removed and linked lists were introduced to add
> > > flexibility to existing structures in attempt to keep their size and
> > > offsets constant and not dependent on features.
> > >
> > > While this is not a complete specification, it describes all the main
> > > structures and should be enough to make sure the idea is solid before
> > > going into implementation specifics.
> > >
> > > A new virtio-pci capability structure will be introduced. This structure
> > > will be used to describe the basics of a virtio-pci device. The
> > > structure is actually a PCI capability structure which wraps the new virtio-pci
> > > capability structure:
> > >
> > > +------------++------------+------------+------------+--------------+-----------------
> > > | Bits || 8 | 8 | 8 | 8 | Cap specific
> > > +------------++------------+------------+------------+--------------+-----------------
> > > | Read/Write || R | R | R | R | Cap specific
> > > +------------++------------+------------+------------+--------------+-----------------
> > > | Purpose || Capability | Capability | virtio-pci | virtio-pci | Cap specific
> > > | || ID | Next PTR | Cap ID | Next Cap PTR |
> > > +------------++------------+------------+------------+--------------+-----------------
> > >
> > > Currently, only one virtio-pci capability is defined, and is the one that defines
> > > the layout of the virtio-pci config space.
> > >
> > > VIRTIO_PCI_C_LAYOUT:
> > >
> > > +------------++---------------+---------------+-----------------+-----------------+
> > > | Bits || 29 | 3 | 29 | 3 |
> > > +------------++---------------+---------------+-----------------+-----------------+
> > > | Read/Write || R | R | R | R |
> > > +------------++---------------+---------------+-----------------+-----------------+
> > > | Purpose || Common config | Common config | Device specific | Device specific |
> > > | || Offset | BIR | Offset | BIR |
> > > +------------++---------------+---------------+-----------------+-----------------+
> >
> > I'm implementing a different layout, with
> > separate capabilities for common and device specific
> > fields.
>
> Which is what I have here, no?

No :) Give me a couple of hours I'll send an RFC patch so you can see
what I mean.

> --
>
> Sasha.


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