On 21/05/2018 17:02, Peter Maydell wrote: > On 21 May 2018 at 15:34, Paolo Bonzini <pbonz...@redhat.com> wrote: >> Why do the levels have to be migrated at all? It should be enough if >> the IRQ level is either migrated manually, or restored (e.g. in >> post_save callbacks) through other data that is migrated. > This is standard behaviour for devices: they track their > inbound irq/gpio lines, and then that becomes internal state for > them that must be migrated.
But or_irq's input are another device's outbound lines, so tracking them should not be necessary. The other device would do it for or_irq. Paolo > If we didn't migrate the input line state, then after a migration > the levels[] array would be all zeroes, and the next time a > connected device signalled a high-to-low transition we'd take > the output line low even if it should not be (because we'd have > forgotten that some other input lines were high). > > In a different world, the state would be in the qemu_irq line itself > (in the same way that in hardware signal lines are their own state), > but we can't get there from here.
