Re: [qemu-s390x] [PATCH v3 09/33] add doc about Resettable interface

[David Gibson]

On Wed, Aug 07, 2019 at 05:01:42PM +0100, Peter Maydell wrote:
> On Wed, 31 Jul 2019 at 07:33, David Gibson <address@hidden> wrote:
> >
> > On Mon, Jul 29, 2019 at 04:56:30PM +0200, Damien Hedde wrote:
> > > Signed-off-by: Damien Hedde <address@hidden>
> > > +For Devices and Buses there is also the corresponding helpers:
> > > +void device_reset(Device *dev, bool cold)
> > > +void bus_reset(Device *dev, bool cold)
> >
> > What's the semantic difference between resetting a bus and resetting
> > the bridge device which owns it?
> 
> We should definitely explain this in the documentation, but
> consider for instance a SCSI controller. Resetting the
> SCSI controller puts all its registers back into whatever
> the reset state is for the device, as well as resetting
> everything on the SCSI bus. Resetting just the SCSI bus
> resets the disks and so on on the bus, but doesn't change
> the state of the controller itself, which remains programmed
> with whatever state the guest has set up.
> 
> PCI has a similar distinction between resetting the controller
> and resetting the bus.
> 
> Note that we have this distinction in the current APIs too:
> qbus_reset_all() vs qdev_reset_all().

Yeah, sorry, I didn't express my concern very well... and now I've
kind of forgotten the details of it.  I think the oddities you also
pointed out with the state saving made me think the two were
sorta equivalent in this patchset, but the interface suggested otherwise.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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