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Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and
From: |
Anthony Liguori |
Subject: |
Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices |
Date: |
Mon, 07 Jan 2013 14:20:35 -0600 |
User-agent: |
Notmuch/0.13.2+93~ged93d79 (http://notmuchmail.org) Emacs/23.3.1 (x86_64-pc-linux-gnu) |
Peter Maydell <address@hidden> writes:
> On 7 January 2013 19:10, Anthony Liguori <address@hidden> wrote:
>> Paolo Bonzini <address@hidden> 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.
I don't mean a BusState level concept, I mean a PCIBus concept.
There is clearly such a thing as a PCI bus reset. In fact, there are
multiple types of PCI bus resets. There should be a PCIBus method that
calls out to PCIDevices on the bus.
But that isn't something that should be fitted into generalized to a
BusState::reset method.
> 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.
Agreed.
>
> 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 :-)
Yes, and that's basically what qemu_system_reset() is. Of course, we
model it like everything is directly connected to a single power source
which is true 99% of the time. That's why we've gotten away with it for
so long.
Regards,
Anthony Liguori
> -- PMM
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Anthony Liguori, 2013/01/07
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Michael S. Tsirkin, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Michael S. Tsirkin, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Michael S. Tsirkin, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Paolo Bonzini, 2013/01/09
- Re: [Qemu-devel] [PATCH 00/15] qdev: make reset semantics more clear and consistent, reset qbuses under virtio devices, Anthony Liguori, 2013/01/09