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

[Cornelia Huck <cohuck@redhat.com>]

On Tue, 30 Jul 2019 16:08:59 +0200
Damien Hedde <damien.hedde@greensocs.com> wrote:

> On 7/30/19 3:59 PM, Peter Maydell wrote:
> > 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.

Ah ok, that makes sense.

> >   
> 
> Exactly. In the following patches, I've tried to replace existing reset
> calls by cold or warm reset depending on whether:
> + it is called through the main system reset -> cold
> + it is called during normal life-time       -> warm
> 
> But I definitely can add some docs/comments to better explain that.

Yes, that would be great; I think I now understand enough for looking
at the patches.