Re: [Qemu-devel] [PATCH v3 01/33] Create Resettable QOM interface

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 30 Jul 2019 at 14:56, Cornelia Huck <cohuck@redhat.com> wrote:
>
> On Tue, 30 Jul 2019 14:44:21 +0100
> Peter Maydell <peter.maydell@linaro.org> wrote:
>
> > On Tue, 30 Jul 2019 at 14:42, Cornelia Huck <cohuck@redhat.com> wrote:
> > > I'm having a hard time figuring out what a 'cold' or a 'warm' reset is
> > > supposed to be... can you add a definition/guideline somewhere?
> >
> > Generally "cold" reset is "power on" and "warm" is "we were already
> > powered-on, but somebody flipped a reset line somewhere".
>
> Ok, that makes sense... my main concern is to distinguish that in a
> generic way, as it is a generic interface. What about adding something
> like:
>
> "A 'cold' reset means that the object to be reset is initially reset; a 'warm'
> reset means that the object to be reset has already been initialized."
>
> Or is that again too generic?

I think it doesn't quite capture the idea -- an object can have already
been reset and then get a 'cold' reset: this is like having a powered-on
machine and then power-cycling it.

The 'warm' reset is the vaguer one, because the specific behaviour
is somewhat device-dependent (many devices might not have any
difference from 'cold' reset, for those that do the exact detail
of what doesn't get reset on warm-reset will vary). But every
device should have some kind of "as if you power-cycled it" (or
for QEMU, "go back to the same state as if you just started QEMU on the
command line"). Our current "reset" method is really cold-reset.

thanks
-- PMM