On Tue, Oct 05, 2021 at 01:13:31PM +0200, Cornelia Huck wrote: > On Tue, Oct 05 2021, Halil Pasic <pasic@xxxxxxxxxxxxx> wrote: > > > On Mon, 4 Oct 2021 05:07:13 -0400 > > "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > >> Well we established that we can know. Here's an alternative explanation: > > > > > > I thin we established how this should be in the future, where a transport > > specific mechanism is used to decide are we operating in legacy mode or > > in modern mode. But with the current QEMU reality, I don't think so. > > Namely currently the switch native-endian config -> little endian config > > happens when the VERSION_1 is negotiated, which may happen whenever > > the VERSION_1 bit is changed, or only when FEATURES_OK is set > > (vhost-user). > > > > This is consistent with device should detect a legacy driver by checking > > for VERSION_1, which is what the spec currently says. > > > > So for transitional we start out with native-endian config. For modern > > only the config is always LE. > > > > The guest can distinguish between a legacy only device and a modern > > capable device after the revision negotiation. A legacy device would > > reject the CCW. > > > > But both a transitional device and a modern only device would accept > > a revision > 0. So the guest does not know for ccw. > > Well, for pci I think the driver knows that it is using either legacy or > modern, no? > > And for ccw, the driver knows at that point in time which revision it > negotiated, so it should know that a revision > 0 will use LE (and the > device will obviously know that as well.) > > Or am I misunderstanding what you're getting at? Exactly what I'm saying.
