Re: [PATCH v3 1/2] dt-bindings: iommu: add bindings for sprd iommu

[Chunyan Zhang]

Hi Rob,

On Fri, 5 Feb 2021 at 07:25, Rob Herring <robh@xxxxxxxxxx> wrote:
>
> On Wed, Feb 03, 2021 at 05:07:26PM +0800, Chunyan Zhang wrote:
> > From: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
> >
> > This iommu module can be used by Unisoc's multimedia devices, such as
> > display, Image codec(jpeg) and a few signal processors, including
> > VSP(video), GSP(graphic), ISP(image), and CPP(camera pixel processor), etc.
> >
> > Signed-off-by: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
> > ---
> >  .../devicetree/bindings/iommu/sprd,iommu.yaml | 72 +++++++++++++++++++
> >  1 file changed, 72 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/iommu/sprd,iommu.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/iommu/sprd,iommu.yaml b/Documentation/devicetree/bindings/iommu/sprd,iommu.yaml
> > new file mode 100644
> > index 000000000000..4fc99e81fa66
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/iommu/sprd,iommu.yaml
> > @@ -0,0 +1,72 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +# Copyright 2020 Unisoc Inc.
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/iommu/sprd,iommu.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Unisoc IOMMU and Multi-media MMU
> > +
> > +maintainers:
> > +  - Chunyan Zhang <zhang.lyra@xxxxxxxxx>
> > +
> > +properties:
> > +  compatible:
> > +    enum:
> > +      - sprd,iommu-v1
> > +
> > +  "#iommu-cells":
> > +    const: 0
> > +    description:
> > +      Unisoc IOMMUs are all single-master IOMMU devices, therefore no
> > +      additional information needs to associate with its master device.
> > +      Please refer to the generic bindings document for more details,
> > +      Documentation/devicetree/bindings/iommu/iommu.txt
> > +
> > +  reg:
> > +    maxItems: 1
> > +    description:
> > +      Not required if 'sprd,iommu-regs' is defined.
> > +
> > +  clocks:
> > +    description:
> > +      Reference to a gate clock phandle, since access to some of IOMMUs are
> > +      controlled by gate clock, but this is not required.
> > +
> > +  sprd,iommu-regs:
> > +    $ref: /schemas/types.yaml#/definitions/phandle-array
> > +    description:
> > +      Reference to a syscon phandle plus 1 cell, the syscon defines the
> > +      register range used by the iommu and the media device, the cell
> > +      defines the offset for iommu registers. Since iommu module shares
> > +      the same register range with the media device which uses it.
> > +
> > +required:
> > +  - compatible
> > +  - "#iommu-cells"
> > +
> > +oneOf:
> > +  - required:
> > +      - reg
> > +  - required:
> > +      - sprd,iommu-regs
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    iommu_disp: iommu-disp {
> > +      compatible = "sprd,iommu-v1";
> > +      sprd,iommu-regs = <&dpu_regs 0x800>;
>
> If the IOMMU is contained within another device, then it should just be
> a child node of that device.

Yes, actually IOMMU can be seen as a child of multimedia devices, I
considered moving IOMMU under into multimedia device node, but
multimedia devices need IOMMU when probe[1], so I dropped that idea.

And they share the same register base, e.g.

+               mm {
+                       compatible = "simple-bus";
+                       #address-cells = <2>;
+                       #size-cells = <2>;
+                       ranges;
+
+                       dpu_regs: syscon@63000000 {
+                               compatible = "sprd,sc9863a-dpuregs", "syscon";
+                               reg = <0 0x63000000 0 0x1000>;
+                       };
+
+                       dpu: dpu@63000000 {
+                               compatible = "sprd,sharkl3-dpu";
+                               sprd,disp-regs = <&dpu_regs>;
+                               iommus = <&iommu_dispc>;
+                       };
+
+                       iommu_dispc: iommu@63000000 {
+                               compatible = "sprd,iommu-v1";
+                               sprd,iommu-regs = <&dpu_regs 0x800>;
+                               #iommu-cells = <0>;
+                        };

DPU use the registers from 0, IOMMU from 0x800, the purpose of using
syscon node was to avoid remapping register physical address.

> Or just make 'dpu_regs' an IOMMU provider
> (i.e. just add #iommu-cells to it).

xxx_regs(syscon node) defines the register range for IOMMU and a
multimedia device (such as dpu, image codec, etc.)

Hope I've explained the relationship of xxx_regs, multimedia device,
and iommu clearly :)

Any suggestion for this kind of cases?

Thanks,
Chunyan

[1] https://elixir.bootlin.com/linux/v5.11-rc6/source/drivers/iommu/of_iommu.c#L145
>
> > +      #iommu-cells = <0>;
> > +    };
> > +
> > +  - |
> > +    iommu_jpg: iommu-jpg {
> > +      compatible = "sprd,iommu-v1";
> > +      sprd,iommu-regs = <&jpg_regs 0x300>;
> > +      #iommu-cells = <0>;
> > +      clocks = <&mm_gate 1>;
> > +    };
> > +
> > +...
> > --
> > 2.25.1
> >