Re: [PATCH 4/5] hw/arm/smmuv3: Move reset to exit phase

[Peter Maydell]

On Fri, 7 Feb 2025 at 17:48, Peter Xu <peterx@redhat.com> wrote:
>
> On Fri, Feb 07, 2025 at 04:58:39PM +0000, Peter Maydell wrote:
> > (I wonder if we ought to suggest quiescing outstanding
> > DMA in the enter phase? But it's probably easier to fix
> > the iommus like this series does than try to get every
> > dma-capable pci device to do something different.)
>
> I wonder if we should provide some generic helper to register vIOMMU reset
> callbacks, so that we'll be sure any vIOMMU model impl that will register
> at exit() phase only, and do nothing during the initial two phases.  Then
> we can put some rich comment on that helper on why.
>
> Looks like it means the qemu reset model in the future can be a combination
> of device tree (which resets depth-first) and the three phases model.  We
> will start to use different approach to solve different problems.

The tree of QOM devices (i.e. the one based on the qbus buses
and rooted at the sysbus) resets depth-first, but it does so in
three phases: first we traverse everything doing 'enter'; then
we traverse everything doing 'hold'; then we traverse everything
doing 'exit'. There *used* to be an awkward mix of some things
being three-phase and some not, but we have now got rid of all
of those so a system reset does a single three-phase reset run
which resets everything.

-- PMM