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    SubjectRe: [PATCH v3 1/2] dt-bindings: iommu: add bindings for sprd iommu
    On Thu, 11 Feb 2021 at 03:21, Rob Herring <robh@kernel.org> wrote:
    >
    > On Fri, Feb 5, 2021 at 1:21 AM Chunyan Zhang <zhang.lyra@gmail.com> wrote:
    > >
    > > Hi Rob,
    > >
    > > On Fri, 5 Feb 2021 at 07:25, Rob Herring <robh@kernel.org> wrote:
    > > >
    > > > On Wed, Feb 03, 2021 at 05:07:26PM +0800, Chunyan Zhang wrote:
    > > > > From: Chunyan Zhang <chunyan.zhang@unisoc.com>
    > > > >
    > > > > 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@unisoc.com>
    > > > > ---
    > > > > .../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@gmail.com>
    > > > > +
    > > > > +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.
    >
    > Don't design your binding around working-around linux issues.
    >
    > > And they share the same register base, e.g.
    > >
    > > + mm {
    > > + compatible = "simple-bus";
    > > + #address-cells = <2>;
    > > + #size-cells = <2>;
    > > + ranges;
    > > +
    > > + dpu_regs: syscon@63000000 {
    >
    > Drop this node.
    >
    > > + compatible = "sprd,sc9863a-dpuregs", "syscon";
    > > + reg = <0 0x63000000 0 0x1000>;
    > > + };
    > > +
    > > + dpu: dpu@63000000 {
    > > + compatible = "sprd,sharkl3-dpu";
    > > + sprd,disp-regs = <&dpu_regs>;
    >
    > reg = <0 0x63000000 0 0x800>;
    >
    > > + iommus = <&iommu_dispc>;
    > > + };
    > > +
    > > + iommu_dispc: iommu@63000000 {
    > > + compatible = "sprd,iommu-v1";
    > > + sprd,iommu-regs = <&dpu_regs 0x800>;
    >
    > reg = <0 0x63000800 0 0x800>;

    Alright, considering you deprecate using syscon to map registers here,
    I will drop that.
    But that would cause the same physical address to be mapped two times at least.
    And this is not a single case, since there are a few media devices and
    their IOMMUs which all have this issue.

    Thanks,
    Chunyan

    >
    > > + #iommu-cells = <0>;
    >
    > Though given it seems there is only 1 client and this might really be
    > just 1 h/w block, you don't really need to use the iommu binding at
    > all. The DPU should be able to instantiate it's own IOMMU device.
    > There's other examples of this such as mali GPU though that is all one
    > driver, but that's a Linux implementation detail.
    >
    > Rob

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