On 7 January 2013 19:10, Anthony Liguori <aligu...@us.ibm.com> wrote: > Paolo Bonzini <pbonz...@redhat.com> writes: >> 1) device-level reset is the kind of reset that you get with a register >> write on the device. It will clear interrupts and DMAs among other things, >> but not any bus-level state, for example it will not clear PCI BARs and >> other configuration space data. It is done with qdev_reset_all.
This isn't really right -- often writing the register on the device will reset some things but not the whole device state the way a qdev reset does. qdev reset (to the extent it's modelling anything) is more like yanking power to the device and reapplying it. >> 2) bus-level reset is the kind of reset that you get with a register >> write on the device that exports the bus (including triggering a device-level >> reset on the device that exports the bus). It will do a device-level >> reset on the child, but also clear bus-level state such as PCI BARs and >> other configuration space data. It can be triggered for all devices >> on a bus with qbus_reset_all. There is still no API for a bus-level >> reset of a single device (like PCI FLR), this can be added later. This doesn't sound very plausible: when would you do a bus level reset anyway? > I don't really understand this dual abstraction. I suspect it's > overgeneralizing something that's the result of poor modeling. Agreed. > What I'm missing with this series is what problem are we trying to > solve? I don't think we model reset correctly today because I don't > think there's a single notion of reset. Also agreed. > I think reset really ought to just be a bus level concept with > individual implementations for each bus. I'm not sure I really agree here, especially since QOM/qdev are moving away from the idea that there is a single bus tree and every device is on a single bus. It's quite common for a bus to include a reset signal but not all device reset is handled by a signal on a bus. If we want to model reset properly we should model actual reset lines (and/or power-cycling). If we don't care we can continue with whatever fudge we like :-) -- PMM