On Tue, Aug 13, 2024 at 6:37 PM Peter Maydell <peter.mayd...@linaro.org> wrote: > > On Tue, 13 Aug 2024 at 16:39, Juraj Marcin <jmar...@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 <jmar...@redhat.com> > > Reviewed-by: David Hildenbrand <da...@redhat.com> > > --- > > docs/devel/reset.rst | 8 ++++++++ > > hw/i386/pc.c | 2 +- > > include/hw/resettable.h | 2 ++ > > 3 files changed, 11 insertions(+), 1 deletion(-) > > > > diff --git a/docs/devel/reset.rst b/docs/devel/reset.rst > > index 9746a4e8a0..a7c9467313 100644 > > --- a/docs/devel/reset.rst > > +++ b/docs/devel/reset.rst > > @@ -44,6 +44,14 @@ 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 called for a reset when the system is being woken-up from a > > + suspended state using the ``qemu_system_wakeup()`` function. If the > > machine > > + needs to reset its devices in its ``MachineClass::wakeup()`` method, this > > + reset type should be used, so 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. > > + > > Devices which implement reset methods must treat any unknown ``ResetType`` > > as equivalent to ``RESET_TYPE_COLD``; this will reduce the amount of > > existing code we need to change if we add more types in future. > > diff --git a/hw/i386/pc.c b/hw/i386/pc.c > > index ccb9731c91..49efd0a997 100644 > > --- a/hw/i386/pc.c > > +++ b/hw/i386/pc.c > > @@ -1716,7 +1716,7 @@ static void pc_machine_reset(MachineState *machine, > > ResetType type) > > static void pc_machine_wakeup(MachineState *machine) > > { > > cpu_synchronize_all_states(); > > - pc_machine_reset(machine, RESET_TYPE_COLD); > > + pc_machine_reset(machine, RESET_TYPE_WAKEUP); > > cpu_synchronize_all_post_reset(); > > } > > I'm happy (following discussion in the previous thread) > that 'wakeup' is the right reset event to be using here. > But looking at the existing code for qemu_system_wakeup() > something seems odd here. qemu_system_wakeup() calls > the MachineClass::wakeup method if it's set, and does > nothing if it's not. The PC implementation of that calls > pc_machine_reset(), which does a qemu_devices_reset(), > which does a complete three-phase reset of the system. > But if the machine doesn't implement wakeup then we > never reset the system at all. > > Shouldn't qemu_system_wakeup() do a qemu_devices_reset() > if there's no MachineClass::wakeup, in a similar way to > how qemu_system_reset() does a qemu_devices_reset() > if there's no MachineClass::reset method ? Having the > wakeup event be "sometimes this will do a RESET_TYPE_WAKEUP > but sometimes it won't" doesn't seem right to me...
>From my understanding that I have gathered from the code (but please, someone correct me if I am wrong), this is machine specific. Some machine types might not support suspend+wake-up at all. The support has to be explicitly advertised through qemu_register_wakeup_support() (for example, aarch64 with a generic virt machine type does not advertise support). Even if the machine type advertises suspend+wake-up support, it might not need to do anything machine specific. This is the case of pSeries PowerPC machine (sPAPR) that advertises support, but does not implement MachineClass::wakeup() method as nothing needs to change in the machine state. [1] So, if a restart during wake-up happens, it can be differentiated with the wake-up reset type, and if the machine type does not need to reset its devices during wake-up, there is no reset that needs to be differentiated. [1]: https://gitlab.com/qemu-project/qemu/-/blob/a733f37aef3b7d1d33bfe2716af88cdfd67ba64e/hw/ppc/spapr.c?#L3155 > > thanks > -- PMM > -- Juraj Marcin