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

[Laurentiu Tudor]

On 5/22/2020 5:02 PM, Rob Herring wrote:
> On Fri, May 22, 2020 at 3:42 AM Robin Murphy <robin.murphy at arm.com> wrote:
>>
>> On 2020-05-22 00:10, Rob Herring wrote:
>>> On Thu, May 21, 2020 at 7:00 AM Lorenzo Pieralisi
>>> <lorenzo.pieralisi at arm.com> wrote:
>>>>
>>>> From: Laurentiu Tudor <laurentiu.tudor at 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 at nxp.com>
>>>> Cc: Rob Herring <robh+dt at 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.
>>
>>>> +
>>>> +  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 at 5000000 {
>>>> @@ -128,6 +140,16 @@ Example:
>>>>                  ...
>>>>           };
>>>>
>>>> +       gic: interrupt-controller at 6000000 {
>>>> +               compatible = "arm,gic-v3";
>>>> +               ...
>>>> +               its: gic-its at 6020000 {
>>>> +                       compatible = "arm,gic-v3-its";
>>>> +                       msi-controller;
>>>> +                       ...
>>>> +               };
>>>> +       };
>>>> +
>>>>           fsl_mc: fsl-mc at 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.
> 
> No, it doesn't make sense from a binding perspective.
> 
>>
>>>>                   /* 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 ;)
> 
> I'm referring to the 23 on the left and right, not between the msi and
> iommu. If the left and right are the same, then what are we remapping
> exactly?
> 

I also insisted a lot on keeping things simple and don't do any kind of
translation but Robin convinced me that this is not such a great idea.
The truth is that the hardware can be configured in such a way that the
assumption that icid -> streamid mapping is 1:1 no longer holds.
It just happens that we currently setup the hw to have 1:1 mappings.

P.S. No idea why, but somehow I got dropped from the thread. Weird.

---
Best Regards, Laurentiu