Re: [PATCH 09/12] dt-bindings: arm: fsl: Add msi-map device-tree binding for fsl-mc bus

[Diana Craciun OSS <diana.craciun@oss.nxp.com>]

On 5/22/2020 12:42 PM, Robin Murphy wrote:
> On 2020-05-22 00:10, Rob Herring wrote:
>> On Thu, May 21, 2020 at 7:00 AM Lorenzo Pieralisi
>> <lorenzo.pieralisi@arm.com> wrote:
>>>
>>> From: Laurentiu Tudor <laurentiu.tudor@nxp.com>
>>>
>>> The existing bindings cannot be used to specify the relationship
>>> between fsl-mc devices and GIC ITSes.
>>>
>>> Add a generic binding for mapping fsl-mc devices to GIC ITSes, using
>>> msi-map property.
>>>
>>> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
>>> Cc: Rob Herring <robh+dt@kernel.org>
>>> ---
>>>   .../devicetree/bindings/misc/fsl,qoriq-mc.txt | 30 
>>> +++++++++++++++++--
>>>   1 file changed, 27 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt 
>>> b/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
>>> index 9134e9bcca56..b0813b2d0493 100644
>>> --- a/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
>>> +++ b/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
>>> @@ -18,9 +18,9 @@ same hardware "isolation context" and a 10-bit 
>>> value called an ICID
>>>   the requester.
>>>
>>>   The generic 'iommus' property is insufficient to describe the 
>>> relationship
>>> -between ICIDs and IOMMUs, so an iommu-map property is used to define
>>> -the set of possible ICIDs under a root DPRC and how they map to
>>> -an IOMMU.
>>> +between ICIDs and IOMMUs, so the iommu-map and msi-map properties 
>>> are used
>>> +to define the set of possible ICIDs under a root DPRC and how they 
>>> map to
>>> +an IOMMU and a GIC ITS respectively.
>>>
>>>   For generic IOMMU bindings, see
>>>   Documentation/devicetree/bindings/iommu/iommu.txt.
>>> @@ -28,6 +28,9 @@ Documentation/devicetree/bindings/iommu/iommu.txt.
>>>   For arm-smmu binding, see:
>>>   Documentation/devicetree/bindings/iommu/arm,smmu.yaml.
>>>
>>> +For GICv3 and GIC ITS bindings, see:
>>> +Documentation/devicetree/bindings/interrupt-controller/arm,gic-v3.yaml. 
>>>
>>> +
>>>   Required properties:
>>>
>>>       - compatible
>>> @@ -119,6 +122,15 @@ Optional properties:
>>>     associated with the listed IOMMU, with the iommu-specifier
>>>     (i - icid-base + iommu-base).
>>>
>>> +- msi-map: Maps an ICID to a GIC ITS and associated iommu-specifier
>>> +  data.
>>> +
>>> +  The property is an arbitrary number of tuples of
>>> +  (icid-base,iommu,iommu-base,length).
>>
>> I'm confused because the example has GIC ITS phandle, not an IOMMU.
>>
>> What is an iommu-base?
>
> Right, I was already halfway through writing a reply to say that all 
> the copy-pasted "iommu" references here should be using the 
> terminology from the pci-msi.txt binding instead.

Right, will change it.

>
>>> +
>>> +  Any ICID in the interval [icid-base, icid-base + length) is
>>> +  associated with the listed GIC ITS, with the iommu-specifier
>>> +  (i - icid-base + iommu-base).
>>>   Example:
>>>
>>>           smmu: iommu@5000000 {
>>> @@ -128,6 +140,16 @@ Example:
>>>                  ...
>>>           };
>>>
>>> +       gic: interrupt-controller@6000000 {
>>> +               compatible = "arm,gic-v3";
>>> +               ...
>>> +               its: gic-its@6020000 {
>>> +                       compatible = "arm,gic-v3-its";
>>> +                       msi-controller;
>>> +                       ...
>>> +               };
>>> +       };
>>> +
>>>           fsl_mc: fsl-mc@80c000000 {
>>>                   compatible = "fsl,qoriq-mc";
>>>                   reg = <0x00000008 0x0c000000 0 0x40>,    /* MC 
>>> portal base */
>>> @@ -135,6 +157,8 @@ Example:
>>>                   msi-parent = <&its>;
>
> Side note: is it right to keep msi-parent here? It rather implies that 
> the MC itself has a 'native' Device ID rather than an ICID, which I 
> believe is not strictly true. Plus it's extra-confusing that it 
> doesn't specify an ID either way, since that makes it look like the 
> legacy PCI case that gets treated implicitly as an identity msi-map, 
> which makes no sense at all to combine with an actual msi-map.

Before adding msi-map, the fsl-mc code assumed that ICID and streamID 
are equal and used msi-parent just to get the reference to the ITS node. 
Removing msi-parent will break the backward compatibility of the already 
existing systems. Maybe we should mention that this is legacy and not to 
be used for newer device trees.


>
>>>                   /* define map for ICIDs 23-64 */
>>>                   iommu-map = <23 &smmu 23 41>;
>>> +                /* define msi map for ICIDs 23-64 */
>>> +                msi-map = <23 &its 23 41>;
>>
>> Seeing 23 twice is odd. The numbers to the right of 'its' should be an
>> ITS number space.
>
> On about 99% of systems the values in the SMMU Stream ID and ITS 
> Device ID spaces are going to be the same. Nobody's going to bother 
> carrying *two* sets of sideband data across the interconnect if they 
> don't have to ;)
>
> Robin.

Diana


>
>>>                   #address-cells = <3>;
>>>                   #size-cells = <1>;
>>>
>>> -- 
>>> 2.26.1
>>>
>> _______________________________________________
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>> iommu@lists.linux-foundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>>

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