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

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

Hi

On 2/7/20 11:24 AM, Michael S. Tsirkin wrote:
> 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 <eric.auger@redhat.com>
>>> Suggested-by: Michael S. Tsirkin <mst@redhat.com>
>> [...]
>>> @@ -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-.

Let's rephrase my previous answer. Once we get the topology description
feature we can leave the x-dt-binding property supported but do not test
it anymore and document it at deprecated?

Thanks

Eric
>