On Tue, 16 Feb 2021 at 23:10, Robin Murphy <robin.murphy@xxxxxxx> wrote: > > On 2021-02-10 19:21, Rob Herring wrote: > > On Fri, Feb 5, 2021 at 1:21 AM Chunyan Zhang <zhang.lyra@xxxxxxxxx> wrote: > >> > >> 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" > > OK, so apparently the hardware is not quite as trivial as my initial > impression, and you should have interrupts as well. Ok, I will have a look. > > >>>> + > >>>> +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. > > Having stumbled across the DRM driver patches the other day, I now see > where this is coming from, and it's even worse than that - this whole > binding seems to be largely working around bad driver design. > I guess you mean bad h/w design (not bad driver design)? Having this syscon node just because I don't want a same register range to be mapped to multiple virtual address ranges, and that's the case for many media devices and their IOMMUs. If this issue exsists for one device only, I can even endure, but that's not unfortunately. But anyway, as you all think this is not a good way, I will change to use reg property. > >> 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>; > > In fact judging by the other driver it looks like the length only needs > to be 0x200 here (but maybe there's more to come in future). > > >> + iommus = <&iommu_dispc>; > >> + }; > >> + > >> + iommu_dispc: iommu@63000000 { > >> + compatible = "sprd,iommu-v1"; > >> + sprd,iommu-regs = <&dpu_regs 0x800>; > > > > reg = <0 0x63000800 0 0x800>; > > ...and this one looks to need less than 0x80, even :) There're some registers not be added in the current driver indeed. The specification defines registers up to 0x7c. > > > > >> + #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. > > FWIW that's really a very different situation - the MMUs in a Mali GPU > are fundamental parts of its internal pipelines and would never make > sense to handle as separate devices (if it were even feasible to try). > An IOMMU like this one is typically a logically-distinct block stuck to > the external bus interface of any old device, rewriting transactions > that said device has already issued - it's telling that it needs to > allocate the prot_page scratchpad for "faulting" transactions to still > flow somewhere, implying that it's not even involved enough to be able > to terminate them. > > As such I think it *does* make complete sense to describe even > "dedicated" IOMMUs like this one, Rockchip, Exynos, etc. in DT. > Otherwise you'd be effectively forcing OSes to turn half their > display/media drivers into mini board files with secret knowledge of > which blocks are integrated with IOMMUs on which SoCs. > Thanks for helping me explain the situation. Regards, Chunyan > Robin.
