On 2020-05-22 15:08, Rob Herring wrote:
On Fri, May 22, 2020 at 3:57 AM Diana Craciun OSS
<diana.crac...@oss.nxp.com> wrote:

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.pieral...@arm.com> wrote:

From: Laurentiu Tudor <laurentiu.tu...@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.tu...@nxp.com>
Cc: Rob Herring <robh...@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
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
-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
@@ -28,6 +28,9 @@ Documentation/devicetree/bindings/iommu/iommu.txt.
   For arm-smmu binding, see:

+For GICv3 and GIC ITS bindings, see:

   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).

           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.

If ids are 1:1, then the DT should use msi-parent. If there is
remapping, then use msi-map. A given system should use one or the
other. I suppose if some ids are 1:1 and the msi-map was added to add
additional support for ids not 1:1, then you could end up with both.
That's fine in dts files, but examples should reflect the 'right' way.

Is that defined anywhere? The generic MSI binding just has some weaselly wording about buses:

"When #msi-cells is non-zero, busses with an msi-parent will require additional properties to describe the relationship between devices on the bus and the set of MSIs they can potentially generate."

which appears at odds with its own definition of msi-parent as including an msi-specifier (or at best very unclear about what value that specifier should take in this case).

The PCI MSI binding goes even further and specifically reserves msi-parent for cases where there is no sideband data. As far as I'm aware, the fact that the ITS driver implements a bodge for the "empty msi-parent even though #msi-cells > 0" case is merely a compatibility thing for old DTs from before this was really thought through, not an officially-specified behaviour.

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