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

[Eric Auger <eric.auger@redhat.com>]

Hi Peter,


On 2/7/25 6:47 PM, Peter Xu 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.
As discussed with Cédric, I think it shall think about having eventually
a base class for vIOMMU. Maybe this is something we can handle
afterwards though.
>
> 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.
>
> Maybe after we settle our mind, we should update the reset document,
> e.g. for device emulation developers, we need to be clear on where to
> quiesce the DMAs, and it must not happen at exit().  Both all devices and
> all iommu impls need to follow the rules to make it work like the plan.
The 3 phase documentation already states that you shouldn't do anything
in enter phase that can have side-effect on other devices. However I
agree we can add another example besides the qemu_irq line one.

Eric
>
> Thanks,
>