-----Original Message-----
From: Robin Murphy [mailto:robin.murphy at arm.com]
Sent: Monday, March 05, 2018 20:23
To: Nipun Gupta <redacted>; will.deacon at arm.com;
mark.rutland at arm.com; catalin.marinas at arm.com
Cc: iommu at lists.linux-foundation.org; robh+dt at kernel.org; hch at lst.de;
m.szyprowski at samsung.com; gregkh at linuxfoundation.org; joro at 8bytes.org;
Leo Li [off-list ref]; shawnguo at kernel.org; linux-
kernel at vger.kernel.org; devicetree at vger.kernel.org; linux-arm-
kernel at lists.infradead.org; linuxppc-dev at lists.ozlabs.org; Bharat Bhushan
[off-list ref]; stuyoder at gmail.com; Laurentiu Tudor
[off-list ref]
Subject: Re: [PATCH 1/6] Docs: dt: add fsl-mc iommu-parent device-tree binding

On 05/03/18 14:29, Nipun Gupta wrote:

quoted

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"?

Hi Robin,

With 'msi-parent' the property is fixed up to have msi-map. In this case there is
no fixup required and simple 'iommu-parent' property can be used, with MC bus
itself providing the stream-id's (in the code execution via FW).

We can also use the iommu-map property similar to PCI, which will require u-boot
fixup. But then it leads to little bit complications of u-boot - kernel compatibility.

If you suggest we can re-use the iommu-map property. What is your opinion?

Thanks,
Nipun

quoted

Signed-off-by: Nipun Gupta <redacted>
---
  .../devicetree/bindings/misc/fsl,qoriq-mc.txt      | 31

++++++++++++++++++++++

quoted

  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

quoted

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

quoted

  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.

quoted

+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 at 5000000 {
+               compatible = "arm,mmu-500";
+               #iommu-cells = <1>;
+               stream-match-mask = <0x7C00>;
+               ...
+        };
+
          fsl_mc: fsl-mc at 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>;