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

[Christophe de Dinechin <dinechin@redhat.com>]

Peter Maydell writes:

> 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.

Is there any concept of locality associated with warm reset?
For example, you'd expect a cold reset to happen on the whole system,
but I guess a warm reset could be restricted to a single bus.

The documentation should give examples of how warm reset could be
triggered, and what it could do differently from cold reset.

>
> thanks
> -- PMM


--
Cheers,
Christophe de Dinechin (IRC c3d)