On Wed, Oct 02, 2013 at 10:02:28AM +0930, Rusty Russell wrote:
> "Michael S. Tsirkin" <> writes:
> > On Thu, Sep 26, 2013 at 11:35:53AM +0930, Rusty Russell wrote:
> >> How about a PCI note something like:
> >>
> >> If a device does not support legacy mode, and is on a platform
> >> where a legacy device with the same ID has previously existed,
> >> it MUST take the following steps to fail gracefully when a
> >> legacy driver attempts to drive it:
> >>
> >> 1) Present no I/O BAR, and no BAR 0, OR
> >> 2) Respond to a single-byte zero write to offset 18 of any I/O
> >> BAR or BAR0 by presenting zeroes on every BAR and ignoring
> >> writes.
> >>
> >> This means it presents 0 virtqueues; at the very least, it makes the
> >> device harmless.
> >>
> >> Note that I didn't specify that it should only be the first write: think
> >> of the kexec case, where an OS crash causes an older OS to come in and
> >> try to reset the device...
> >>
> >> Would that work?
> >> Rusty.
> >
> > So I guess we can also suggest revision id > 0 for pci
> > and > 1 for mmio for non transitional devices.
>
> Only if mmio changes its layout in an incompatible way: that's not
> confimed yet. Otherwise there's no reason to worry about older drivers
> as the device can fail gracefully when feature 32 isn't acknowledged.
>
> > At least with recent windows drivers, this will be enough
> > to not make them bind, and it will also work for
> > linux drivers.
> >
> > Question: what to do if we want do create a non transitional
> > device on ccw?
>
> I think they're happy with their current layout, but I leave this to
> Cornelia (CC'd, but she's still away).
>
> Cheers,
> Rusty.
Well this means they aren't interested in addressing
https://tools.oasis-open.org/issues/browse/VIRTIO-40
?
Also, endian-ness change if it goes through is enough to
break drivers in weird ways, isn't it?
--
MST
