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

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

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?

thanks
-- PMM