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

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Date:   Mon, 5 Mar 2018 14:53:21 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Nipun Gupta <nipun.gupta@....com>, will.deacon@....com,
        mark.rutland@....com, catalin.marinas@....com
Cc:     iommu@...ts.linux-foundation.org, robh+dt@...nel.org, hch@....de,
        m.szyprowski@...sung.com, gregkh@...uxfoundation.org,
        joro@...tes.org, leoyang.li@....com, shawnguo@...nel.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, bharat.bhushan@....com,
        stuyoder@...il.com, laurentiu.tudor@....com
Subject: Re: [PATCH 1/6] Docs: dt: add fsl-mc iommu-parent device-tree binding

On 05/03/18 14:29, 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.

Given that allowing "msi-parent" for #msi-cells > 1 is merely a 
backward-compatibility bodge full of hard-coded assumptions, why would 
we want to knowingly introduce a similarly unpleasant equivalent for 
IOMMUs? What's wrong with "iommu-map"?

> Signed-off-by: Nipun Gupta <nipun.gupta@....com>
> ---
>   .../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.

IOW, precisely the case for which "{msi,iommu}-map" exist. Yes, I know 
they're currently documented under bindings/pci, but they're not really 
intended to be absolutely PCI-specific.

Robin.

> +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.
> +
> +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.
>   
>   Example:
>   
> +        smmu: iommu@...0000 {
> +               compatible = "arm,mmu-500";
> +               #iommu-cells = <1>;
> +               stream-match-mask = <0x7C00>;
> +               ...
> +        };
> +
>           fsl_mc: fsl-mc@...000000 {
>                   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>;
>   
>