Re: [PATCH v2 1/5] dt-bindings: virtio: Specify #iommu-cells value for a virtio-iommu

[Jean-Philippe Brucker <jean-philippe.brucker@arm.com>]

On 25/06/18 20:27, Rob Herring wrote:
> On Thu, Jun 21, 2018 at 08:06:51PM +0100, Jean-Philippe Brucker wrote:
>> A virtio-mmio node may represent a virtio-iommu device. This is discovered
>> by the virtio driver at probe time, but the DMA topology isn't
>> discoverable and must be described by firmware. For DT the standard IOMMU
>> description is used, as specified in bindings/iommu/iommu.txt and
>> bindings/pci/pci-iommu.txt. Like many other IOMMUs, virtio-iommu
>> distinguishes masters by their endpoint IDs, which requires one IOMMU cell
>> in the "iommus" property.
>>
>> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
>> ---
>>  Documentation/devicetree/bindings/virtio/mmio.txt | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/virtio/mmio.txt b/Documentation/devicetree/bindings/virtio/mmio.txt
>> index 5069c1b8e193..337da0e3a87f 100644
>> --- a/Documentation/devicetree/bindings/virtio/mmio.txt
>> +++ b/Documentation/devicetree/bindings/virtio/mmio.txt
>> @@ -8,6 +8,14 @@ Required properties:
>>  - reg:		control registers base address and size including configuration space
>>  - interrupts:	interrupt generated by the device
>>  
>> +Required properties for virtio-iommu:
>> +
>> +- #iommu-cells:	When the node describes a virtio-iommu device, it is
>> +		linked to DMA masters using the "iommus" property as
>> +		described in devicetree/bindings/iommu/iommu.txt. For
>> +		virtio-iommu #iommu-cells must be 1, each cell describing
>> +		a single endpoint ID.
> 
> The iommus property should also be documented for the client side.

Isn't section "IOMMU master node" of iommu.txt sufficient? Since the
iommus property applies to any DMA master, not only virtio-mmio devices,
the canonical description in iommu.txt seems the best place for it, and
I'm not sure what to add in this file. Maybe a short example below the
virtio_block one?

Thanks,
Jean