Re: [PATCH v3 1/2] dt-bindings: arm: xen: document Xen iommu device

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Wed, 26 Jan 2022, Robin Murphy wrote:
> On 2022-01-26 15:09, Sergiy Kibrik wrote:
> > Hi Robin,
> > 
> > > 
> > > This could break Linux guests, since depending on the deferred probe
> > > timeout setting it could lead to drivers never probing because the "IOMMU"
> > > never becomes available.
> > > 
> > 
> > I've noticed no deferred probe timeouts when booting with this patch. Could
> > you please explain more on how this would break guests?
> 
> Right now I think it would actually require command-line intervention, e.g.
> "fw_devlink=on" or "deferred_probe_timeout=3600" (with modules enabled for the
> latter to take full effect), but I'm wary of the potential for future config
> options to control those behaviours by default.

If deferred_probe_timeout=3600 was specified, we would just need an
IOMMU driver in Linux for the "xen,iommu-el2-v1" node to solve the
problem, right? I guess I am trying to say that it wouldn't be a device
tree interface problem but rather a Linux implementation discussion.