On Wed, Jan 26, 2022 at 10:56:39AM -0800, Stefano Stabellini wrote: > 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. fw_devlink=on is now the default (for at least a couple of cycles). > > 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. You would have to add that IOMMU driver to old, existing kernels if you want compatibility with a new DT. Otherwise, that kernel would stop booting with a new DT. Rob
