Re: [PATCH 2/4] reset: Add RESET_TYPE_WAKEUP

[David Hildenbrand]

On 08.08.24 17:28, Juraj Marcin wrote:
> On Thu, Aug 8, 2024 at 2:18 PM Peter Maydell <peter.maydell@linaro.org> wrote:
> > On Tue, 6 Aug 2024 at 17:08, Juraj Marcin <jmarcin@redhat.com> wrote:
> > > Some devices need to distinguish cold start reset from waking up from a
> > > suspended state. This patch adds new value to the enum, and updates the
> > > i386 wakeup method to use this new reset type.
> > >
> > > Signed-off-by: Juraj Marcin <jmarcin@redhat.com>
> > > ---
> > >   docs/devel/reset.rst    | 7 +++++++
> > >   hw/i386/pc.c            | 2 +-
> > >   include/hw/resettable.h | 2 ++
> > >   3 files changed, 10 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/docs/devel/reset.rst b/docs/devel/reset.rst
> > > index 9746a4e8a0..30c9a0cc2b 100644
> > > --- a/docs/devel/reset.rst
> > > +++ b/docs/devel/reset.rst
> > > @@ -44,6 +44,13 @@ The Resettable interface handles reset types with an enum 
> > > ``ResetType``:
> > >     value on each cold reset, such as RNG seed information, and which they
> > >     must not reinitialize on a snapshot-load reset.
> > >
> > > +``RESET_TYPE_WAKEUP``
> > > +  This type is used when the machine is woken up from a suspended state (deep
> > > +  sleep, suspend-to-ram). Devices that must not be reset to their initial state
> > > +  after wake-up (for example virtio-mem) can use this state to differentiate
> > > +  cold start from wake-up can use this state to differentiate cold start from
> > > +  wake-up.
> >
> > I feel like this needs more clarity about what this is, since
> > as a reset type it's a general behaviour, not a machine
> > specific one. What exactly is "wakeup" and when does it happen?
> > How does it differ from what you might call a "warm" reset,
> > where the user pressed the front-panel reset button?
> > Why is virtio-mem in particular interesting here?
>
> Thank you for the feedback!
>
> I have rewritten the paragraph:
>
> This type is called for a reset when the system is being woken up from
> a suspended state using the ``qemu_system_wakeup()`` function. If the
> machine type needs to reset in its ``MachineClass::wakeup()`` method,
> this reset type should be used so that devices can differentiate
> system wake-up from other reset types. For example, a virtio-mem
> device must not unplug its memory during wake-up, as that would clear
> the guest RAM.
>
> Is it clearer? Thank you!

Conceptually, if we want to avoid the "WAKEUP" terminology here, maybe 
we should consider talking about a WARM reset -- in contrast to a COLD one?

During a WARM reset, memory content is supposed to stay untouched, which 
is what we effectively want to achieve with virtio-mem.

Peter, what would be your preference?

--
Cheers,

David / dhildenb