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Subject: Re: [virtio-dev] [PATCH] transitional issues: add new IDs for all devices
On Wed, Oct 02, 2013 at 10:02:28AM +0930, Rusty Russell wrote: > "Michael S. Tsirkin" <mst@redhat.com> 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
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