Re: [PATCH v3 1/2] dt-bindings: iommu: add bindings for sprd iommu
From: Chunyan Zhang
Date: Fri Feb 26 2021 - 01:13:08 EST
On 2021年2月11日 at 03:21, Rob Herring <robh@xxxxxxxxxx> wrote:
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On Fri, Feb 5, 2021 at 1:21 AM Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote:
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> Hi Rob,
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> On Fri, 5 Feb 2021 at 07:25, Rob Herring <robh@xxxxxxxxxx> wrote:
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> >
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> > On Wed, Feb 03, 2021 at 05:07:26PM +0800, Chunyan Zhang wrote:
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> > > From: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
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> > >
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> > > This iommu module can be used by Unisoc's multimedia devices, such as
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> > > display, Image codec(jpeg) and a few signal processors, including
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> > > VSP(video), GSP(graphic), ISP(image), and CPP(camera pixel processor), etc.
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> > >
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> > > Signed-off-by: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
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> > > ---
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> > > .../devicetree/bindings/iommu/sprd,iommu.yaml | 72 +++++++++++++++++++
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> > > 1 file changed, 72 insertions(+)
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> > > create mode 100644 Documentation/devicetree/bindings/iommu/sprd,iommu.yaml
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> > >
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> > > diff --git a/Documentation/devicetree/bindings/iommu/sprd,iommu.yaml b/Documentation/devicetree/bindings/iommu/sprd,iommu.yaml
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> > > new file mode 100644
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> > > index 000000000000..4fc99e81fa66
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> > > --- /dev/null
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> > > +++ b/Documentation/devicetree/bindings/iommu/sprd,iommu.yaml
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> > > @@ -0,0 +1,72 @@
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> > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
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> > > +# Copyright 2020 Unisoc Inc.
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> > > +%YAML 1.2
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> > > +---
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> > > +$id: http://devicetree.org/schemas/iommu/sprd,iommu.yaml#
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> > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
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> > > +
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> > > +title: Unisoc IOMMU and Multi-media MMU
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> > > +
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> > > +maintainers:
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> > > + - Chunyan Zhang <zhang.lyra@xxxxxxxxx>
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> > > +
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> > > +properties:
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> > > + compatible:
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> > > + enum:
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> > > + - sprd,iommu-v1
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> > > +
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> > > + "#iommu-cells":
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> > > + const: 0
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> > > + description:
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> > > + Unisoc IOMMUs are all single-master IOMMU devices, therefore no
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> > > + additional information needs to associate with its master device.
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> > > + Please refer to the generic bindings document for more details,
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> > > + Documentation/devicetree/bindings/iommu/iommu.txt
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> > > +
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> > > + reg:
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> > > + maxItems: 1
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> > > + description:
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> > > + Not required if 'sprd,iommu-regs' is defined.
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> > > +
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> > > + clocks:
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> > > + description:
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> > > + Reference to a gate clock phandle, since access to some of IOMMUs are
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> > > + controlled by gate clock, but this is not required.
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> > > +
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> > > + sprd,iommu-regs:
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> > > + $ref: /schemas/types.yaml#/definitions/phandle-array
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> > > + description:
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> > > + Reference to a syscon phandle plus 1 cell, the syscon defines the
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> > > + register range used by the iommu and the media device, the cell
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> > > + defines the offset for iommu registers. Since iommu module shares
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> > > + the same register range with the media device which uses it.
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> > > +
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> > > +required:
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> > > + - compatible
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> > > + - "#iommu-cells"
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> > > +
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> > > +oneOf:
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> > > + - required:
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> > > + - reg
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> > > + - required:
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> > > + - sprd,iommu-regs
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> > > +
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> > > +additionalProperties: false
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> > > +
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> > > +examples:
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> > > + - |
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> > > + iommu_disp: iommu-disp {
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> > > + compatible = "sprd,iommu-v1";
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> > > + sprd,iommu-regs = <&dpu_regs 0x800>;
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> >
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> > If the IOMMU is contained within another device, then it should just be
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> > a child node of that device.
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> Yes, actually IOMMU can be seen as a child of multimedia devices, I
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> considered moving IOMMU under into multimedia device node, but
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> multimedia devices need IOMMU when probe[1], so I dropped that idea.
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Don't design your binding around working-around linux issues.
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> And they share the same register base, e.g.
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> + mm {
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> + compatible = "simple-bus";
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> + #address-cells = <2>;
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> + #size-cells = <2>;
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> + ranges;
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> +
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> + dpu_regs: syscon@63000000 {
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>
Drop this node.
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> + compatible = "sprd,sc9863a-dpuregs", "syscon";
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> + reg = <0 0x63000000 0 0x1000>;
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> + };
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> +
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> + dpu: dpu@63000000 {
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> + compatible = "sprd,sharkl3-dpu";
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> + sprd,disp-regs = <&dpu_regs>;
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reg = <0 0x63000000 0 0x800>;
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> + iommus = <&iommu_dispc>;
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> + };
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> +
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> + iommu_dispc: iommu@63000000 {
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> + compatible = "sprd,iommu-v1";
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> + sprd,iommu-regs = <&dpu_regs 0x800>;
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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
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> + #iommu-cells = <0>;
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Though given it seems there is only 1 client and this might really be
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just 1 h/w block, you don't really need to use the iommu binding at
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all. The DPU should be able to instantiate it's own IOMMU device.
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There's other examples of this such as mali GPU though that is all one
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driver, but that's a Linux implementation detail.
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>
Rob