Linux Virtualization - Jun 2018 - [PATCH v2 1/5] dt-bindings: virtio: Specify #iommu-cells value for a virtio-iommu

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 at
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.

Rob

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 at
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

On Tue, Jun 26, 2018 at 11:59 AM Jean-Philippe Brucker
<jean-philippe.brucker at arm.com> wrote:
>
> 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 at
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?
No, because somewhere we have to capture if 'iommus' is valid for
'virtio-mmio' or not. Hopefully soon we'll actually be able to
validate that.

Rob