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

From: Rob Herring <robh+dt@kernel.org>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	devicetree@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	Diana Craciun <diana.craciun@oss.nxp.com>,
	PCI <linux-pci@vger.kernel.org>,
	Sudeep Holla <sudeep.holla@arm.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Makarand Pawagi <makarand.pawagi@nxp.com>,
	linux-acpi@vger.kernel.org,
	Linux IOMMU <iommu@lists.linux-foundation.org>,
	Marc Zyngier <maz@kernel.org>, Hanjun Guo <guohanjun@huawei.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	"moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH 09/12] dt-bindings: arm: fsl: Add msi-map device-tree binding for fsl-mc bus
Date: Fri, 22 May 2020 08:02:49 -0600	[thread overview]
Message-ID: <CAL_JsqKVyqc9QZhGD7FeNLpJ=x3oLzmY0zADBa+6ZaE46dN39w@mail.gmail.com> (raw)
In-Reply-To: <abca6ecb-5d93-832f-ff7c-de53bb6203f3@arm.com>

On Fri, May 22, 2020 at 3:42 AM Robin Murphy <robin.murphy@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@arm.com> wrote:
> >>
> >> From: Laurentiu Tudor <laurentiu.tudor@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@nxp.com>
> >> Cc: Rob Herring <robh+dt@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@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.

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?

Rob