RE: RFC: extend iommu-map binding to support #iommu-cells > 1

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> -----Original Message-----
> From: Stuart Yoder
> Sent: Friday, December 16, 2016 8:07 AM
> To: Mark Rutland <mark.rutland@xxxxxxx>; robin.murphy@xxxxxxx;
> will.deacon@xxxxxxx
> Cc: robh+dt@xxxxxxxxxx; Bharat Bhushan <bharat.bhushan@xxxxxxx>;
> Nipun Gupta <nipun.gupta@xxxxxxx>; Diana Madalina Craciun
> <diana.craciun@xxxxxxx>; devicetree@xxxxxxxxxxxxxxx; iommu@lists.linux-
> foundation.org
> Subject: RFC: extend iommu-map binding to support #iommu-cells > 1
> 
> For context, please see the thread:
> https://www.spinics.net/lists/arm-kernel/msg539066.html
> 
> The existing iommu-map binding did not account for the situation where
> #iommu-cells == 2, as permitted in the ARM SMMU binding.  The 2nd cell of
> the IOMMU specifier being the SMR mask.  The existing binding defines the
> mapping as:
>    Any RID r in the interval [rid-base, rid-base + length) is associated with
>    the listed IOMMU, with the iommu-specifier (r - rid-base + iommu-base).
> 
> ...and that does not work if iommu-base is 2 cells, the second being the SMR
> mask.
> 
> While this can be worked around by always having length=1, it seems we can
> get this cleaned up by updating the binding definition for iommu-map.
> 
> See patch below.  Thoughts?
> 
> Thanks,
> Stuart
> 
> -------------------------------------------------------------------------
> 
> diff --git a/Documentation/devicetree/bindings/pci/pci-iommu.txt
> b/Documentation/devicetree/bindings/pci/pci-iommu.txt
> index 56c8296..e81b461 100644
> --- a/Documentation/devicetree/bindings/pci/pci-iommu.txt
> +++ b/Documentation/devicetree/bindings/pci/pci-iommu.txt
> @@ -38,8 +38,20 @@ Optional properties
>    The property is an arbitrary number of tuples of
>    (rid-base,iommu,iommu-base,length).
> 
> -  Any RID r in the interval [rid-base, rid-base + length) is associated with
> -  the listed IOMMU, with the iommu-specifier (r - rid-base + iommu-base).
> +  If the associated IOMMU has an #iommu-cells value of 1, any RID r in
> + the  interval [rid-base, rid-base + length) is associated with the
> + listed IOMMU,  with the iommu-specifier (r - rid-base + iommu-base).
> +
> +  ARM SMMU Note:
> +    The ARM SMMU binding permits an #iommu-cells value of 2 and in this
> +    case defines an IOMMU specifier to be: (stream-id,smr-mask)
> +
> +    In an iommu-map this means the iommu-base consists of 2 cells:
> +        (rid-base,iommu,[stream-id,smr-mask],length).
> +
> +    In this case the RID to IOMMU specifier mapping is defined to be:
> +    any RID r in the interval [rid-base, rid-base + length) is associated
> +    with the listed IOMMU, with the iommu-specifier (r - rid-base + stream-
> id).

Should not this be (r - rid-base + (stream-id & smr-mask)) ?

So basically stream-id ranges from (stream-id & smr-mask) - (stream-id & smr-mask + (length - 1) )

Thanks
-Bharat
> 
>  - iommu-map-mask: A mask to be applied to each Requester ID prior to
> being
>    mapped to an iommu-specifier per the iommu-map property.
> 
> 

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