RE: [PATCH 1/6] Docs: dt: add fsl-mc iommu-parent device-tree binding

[Nipun Gupta]

Hi Rob,

> -----Original Message-----
> From: Rob Herring [mailto:robh@xxxxxxxxxx]
> Sent: Thursday, March 08, 2018 4:10
> To: Nipun Gupta <nipun.gupta@xxxxxxx>
> Cc: will.deacon@xxxxxxx; robin.murphy@xxxxxxx; mark.rutland@xxxxxxx;
> catalin.marinas@xxxxxxx; devicetree@xxxxxxxxxxxxxxx; stuyoder@xxxxxxxxx;
> Bharat Bhushan <bharat.bhushan@xxxxxxx>; gregkh@xxxxxxxxxxxxxxxxxxx;
> joro@xxxxxxxxxx; linuxppc-dev@xxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> Leo Li <leoyang.li@xxxxxxx>; iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx; Laurentiu
> Tudor <laurentiu.tudor@xxxxxxx>; shawnguo@xxxxxxxxxx; hch@xxxxxx; linux-
> arm-kernel@xxxxxxxxxxxxxxxxxxx; m.szyprowski@xxxxxxxxxxx
> Subject: Re: [PATCH 1/6] Docs: dt: add fsl-mc iommu-parent device-tree binding
> 
> On Mon, Mar 05, 2018 at 07:59:21PM +0530, Nipun Gupta wrote:
> > The existing IOMMU bindings cannot be used to specify the relationship
> > between fsl-mc devices and IOMMUs. This patch adds a binding for
> > mapping fsl-mc devices to IOMMUs, using a new iommu-parent property.
> >
> > Signed-off-by: Nipun Gupta <nipun.gupta@xxxxxxx>
> > ---
> >  .../devicetree/bindings/misc/fsl,qoriq-mc.txt      | 31
> ++++++++++++++++++++++
> >  1 file changed, 31 insertions(+)
> >
> > diff --git a/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
> b/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
> > index 6611a7c..011c7d6 100644
> > --- a/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
> > +++ b/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
> > @@ -9,6 +9,24 @@ blocks that can be used to create functional hardware
> objects/devices
> >  such as network interfaces, crypto accelerator instances, L2 switches,
> >  etc.
> >
> > +For an overview of the DPAA2 architecture and fsl-mc bus see:
> > +drivers/staging/fsl-mc/README.txt
> > +
> > +As described in the above overview, all DPAA2 objects in a DPRC share the
> > +same hardware "isolation context" and a 10-bit value called an ICID
> > +(isolation context id) is expressed by the hardware to identify
> > +the requester.
> > +
> > +The generic 'iommus' property is cannot be used to describe the relationship
> > +between fsl-mc and IOMMUs, so an iommu-parent property is used to define
> > +the same.
> 
> Why not? It is just a link between 2 nodes.

We have #iommu-cells as '1' i.e. iommu will have one stream ID configured for a device.
Once USB and other devices start to use IOMMU we will also need this iommu-cells.

When #iommu-cells is defined as '1' and we have 'iommus=<&smmu>' compilation
reports warning about the mismatch.
In fsl-mc bus case we do not have any stream id associated with the bus.

As suggested by Robin, we can simply use the iommu-map property.

> 
> > +
> > +For generic IOMMU bindings, see
> > +Documentation/devicetree/bindings/iommu/iommu.txt.
> > +
> > +For arm-smmu binding, see:
> > +Documentation/devicetree/bindings/iommu/arm,smmu.txt.
> > +
> >  Required properties:
> >
> >      - compatible
> > @@ -88,14 +106,27 @@ Sub-nodes:
> >                Value type: <phandle>
> >                Definition: Specifies the phandle to the PHY device node associated
> >                            with the this dpmac.
> > +Optional properties:
> > +
> > +- iommu-parent: Maps the devices on fsl-mc bus to an IOMMU.
> > +  The property specifies the IOMMU behind which the devices on
> > +  fsl-mc bus are residing.
> 
> If you want a generic property, this should be documented in the common
> binding.

We can use the iommu-map property which is already documented.

> 
> Couldn't you have more than 1 IOMMU upstream of a MC?

There is no such device currently with which fsl-mc bus uses more than one iommu.
Infact, our current systems have only single IOMMU :).

Even in future if such devices are there then we can use iommu-map to specify
more than one iommu with separate requester ID's (RID's).

Thank you for review...

Regards,
Nipun

> 
> >
> >  Example:
> >
> > +        smmu: iommu@5000000 {
> > +               compatible = "arm,mmu-500";
> > +               #iommu-cells = <1>;
> > +               stream-match-mask = <0x7C00>;
> > +               ...
> > +        };
> > +
> >          fsl_mc: fsl-mc@80c000000 {
> >                  compatible = "fsl,qoriq-mc";
> >                  reg = <0x00000008 0x0c000000 0 0x40>,    /* MC portal base */
> >                        <0x00000000 0x08340000 0 0x40000>; /* MC control reg */
> >                  msi-parent = <&its>;
> > +                iommu-parent = <&smmu>;
> >                  #address-cells = <3>;
> >                  #size-cells = <1>;
> >
> > --
> > 1.9.1
> >
> >
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