Re: [PATCH v14 08/11] virtio-iommu-pci: Introduce the x-dt-binding option

[Michael S. Tsirkin]

On Fri, Feb 07, 2020 at 11:05:40AM +0100, Jean-Philippe Brucker wrote:
> Hi Eric,
> 
> On Fri, Feb 07, 2020 at 10:32:00AM +0100, Eric Auger wrote:
> > At the moment, the kernel only supports device tree
> > integration of the virtio-iommu. DT bindings between the
> > PCI root complex and the IOMMU must be created by the machine
> > in conformance to:
> > 
> > Documentation/devicetree/bindings/virtio/iommu.txt.
> > 
> > To make sure the end-user is aware of this, force him to use the
> > temporary device option "x-dt-binding" and also double check the
> > machine has a hotplug handler for the virtio-iommu-pci device.
> > This hotplug handler is in charge of creating those DT bindings.
> > 
> > Signed-off-by: Eric Auger <address@hidden>
> > Suggested-by: Michael S. Tsirkin <address@hidden>
> [...]
> > @@ -39,6 +42,21 @@ static void virtio_iommu_pci_realize(VirtIOPCIProxy 
> > *vpci_dev, Error **errp)
> >      VirtIOIOMMUPCI *dev = VIRTIO_IOMMU_PCI(vpci_dev);
> >      DeviceState *vdev = DEVICE(&dev->vdev);
> >  
> > +    if (!dev->dt_binding) {
> > +        error_setg(errp,
> > +                   "Instantiation currently only is possible if the 
> > machine "
> > +                   "creates device tree iommu-map bindings, ie. ACPI is 
> > not "
> > +                   "yet supported");
> > +        error_append_hint(errp, "use -virtio-iommu-pci,x-dt-binding\n");
> 
> "use -device virtio-iommu-pci,x-dt-binding"?
> 
> Can the option be safely removed as soon as we implement a topology
> description for the remaining platforms?  Or will we need to carry it
> forever for backward-compatibility (ie. ensure that an old command-line
> invocation that contains this option still works)?
> 
> Thanks,
> Jean

I'd worry that if we actually document it then users will come to
depend on it for sure, even though it starts with x-.

-- 
MST