Re: [PATCH 03/11] dt-bindings: Add RISC-V IOMMU bindings

From: Anup Patel
Date: Mon Jul 24 2023 - 08:10:32 EST

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On Mon, Jul 24, 2023 at 5:01 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
>
> On Mon, Jul 24, 2023 at 6:02 PM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
> >
> > On Mon, Jul 24, 2023 at 1:33 PM Zong Li <zong.li@xxxxxxxxxx> wrote:
> > >
> > > On Thu, Jul 20, 2023 at 3:35 AM Tomasz Jeznach <tjeznach@xxxxxxxxxxxx> wrote:
> > > >
> > > > From: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > > >
> > > > We add DT bindings document for RISC-V IOMMU platform and PCI devices
> > > > defined by the RISC-V IOMMU specification.
> > > >
> > > > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > > > ---
> > > > .../bindings/iommu/riscv,iommu.yaml | 146 ++++++++++++++++++
> > > > 1 file changed, 146 insertions(+)
> > > > create mode 100644 Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > > > new file mode 100644
> > > > index 000000000000..8a9aedb61768
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/iommu/riscv,iommu.yaml
> > > > @@ -0,0 +1,146 @@
> > > > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > > > +%YAML 1.2
> > > > +---
> > > > +$id: http://devicetree.org/schemas/iommu/riscv,iommu.yaml#
> > > > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > > > +
> > > > +title: RISC-V IOMMU Implementation
> > > > +
> > > > +maintainers:
> > > > + - Tomasz Jeznach <tjeznach@xxxxxxxxxxxx>
> > > > +
> > > > +description:
> > > > + The RISC-V IOMMU specificaiton defines an IOMMU for RISC-V platforms
> > > > + which can be a regular platform device or a PCI device connected to
> > > > + the host root port.
> > > > +
> > > > + The RISC-V IOMMU provides two stage translation, device directory table,
> > > > + command queue and fault reporting as wired interrupt or MSIx event for
> > > > + both PCI and platform devices.
> > > > +
> > > > + Visit https://github.com/riscv-non-isa/riscv-iommu for more details.
> > > > +
> > > > +properties:
> > > > + compatible:
> > > > + oneOf:
> > > > + - description: RISC-V IOMMU as a platform device
> > > > + items:
> > > > + - enum:
> > > > + - vendor,chip-iommu
> > > > + - const: riscv,iommu
> > > > +
> > > > + - description: RISC-V IOMMU as a PCI device connected to root port
> > > > + items:
> > > > + - enum:
> > > > + - vendor,chip-pci-iommu
> > > > + - const: riscv,pci-iommu
> > > > +
> > > > + reg:
> > > > + maxItems: 1
> > > > + description:
> > > > + For RISC-V IOMMU as a platform device, this represents the MMIO base
> > > > + address of registers.
> > > > +
> > > > + For RISC-V IOMMU as a PCI device, this represents the PCI-PCI bridge
> > > > + details as described in Documentation/devicetree/bindings/pci/pci.txt
> > > > +
> > > > + '#iommu-cells':
> > > > + const: 2
> > > > + description: |
> > > > + Each IOMMU specifier represents the base device ID and number of
> > > > + device IDs.
> > > > +
> > > > + interrupts:
> > > > + minItems: 1
> > > > + maxItems: 16
> > > > + description:
> > > > + The presence of this property implies that given RISC-V IOMMU uses
> > > > + wired interrupts to notify the RISC-V HARTS (or CPUs).
> > > > +
> > > > + msi-parent:
> > > > + description:
> > > > + The presence of this property implies that given RISC-V IOMMU uses
> > > > + MSIx to notify the RISC-V HARTs (or CPUs). This property should be
> > > > + considered only when the interrupts property is absent.
> > > > +
> > > > + dma-coherent:
> > > > + description:
> > > > + Present if page table walks and DMA accessed made by the RISC-V IOMMU
> > > > + are cache coherent with the CPU.
> > > > +
> > > > + power-domains:
> > > > + maxItems: 1
> > > > +
> > >
> > > In RISC-V IOMMU, certain devices can be set to bypass mode when the
> > > IOMMU is in translation mode. To identify the devices that require
> > > bypass mode by default, does it be sensible to add a property to
> > > indicate this behavior?
> >
> > Bypass mode for a device is a property of that device (similar to dma-coherent)
> > and not of the IOMMU. Other architectures (ARM and x86) never added such
> > a device property for bypass mode so I guess it is NOT ADVISABLE to do it.
> >
> > If this is REALLY required then we can do something similar to the QCOM
> > SMMU driver where they have a whitelist of devices which are allowed to
> > be in bypass mode (i.e. IOMMU_DOMAIN_IDENTITY) based their device
> > compatible string and any device outside this whitelist is blocked by default.
> >
>
> I have considered that adding the property of bypass mode to that
> device would be more appropriate. However, if we want to define this
> property for the device, it might need to go through the generic IOMMU
> dt-bindings, but I'm not sure if other IOMMU devices need this. I am
> bringing up this topic here because I would like to explore if there
> are any solutions on the IOMMU side, such as a property that indicates
> the phandle of devices wishing to set bypass mode, somewhat similar to
> the whitelist you mentioned earlier. Do you think we should address
> this? After all, this is a case of RISC-V IOMMU supported.

Bypass mode is a common feature across IOMMUs. Other IOMMUs don't
have a special property for bypass mode at device-level or at IOMMU level,
which clearly indicates that defining a RISC-V specific property is not the
right way to go.

The real question is how do we set IOMMU_DOMAIN_IDENTITY (i.e.
bypass/identity domain) as the default domain for certain devices ?

One possible option is to implement def_domain_type() IOMMU operation
for RISC-V IOMMU which will return IOMMU_DOMAIN_IDENTITY for
certain devices based on compatible string matching (i.e. whitelist of
devices). As an example, refer qcom_smmu_def_domain_type()
of drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c

Regards,
Anup

>
> > Regards,
> > Anup
> >
> > >
> > > > +required:
> > > > + - compatible
> > > > + - reg
> > > > + - '#iommu-cells'
> > > > +
> > > > +additionalProperties: false
> > > > +
> > > > +examples:
> > > > + - |
> > > > + /* Example 1 (IOMMU platform device with wired interrupts) */
> > > > + immu1: iommu@1bccd000 {
> > > > + compatible = "vendor,chip-iommu", "riscv,iommu";
> > > > + reg = <0x1bccd000 0x1000>;
> > > > + interrupt-parent = <&aplic_smode>;
> > > > + interrupts = <32 4>, <33 4>, <34 4>, <35 4>;
> > > > + #iommu-cells = <2>;
> > > > + };
> > > > +
> > > > + /* Device with two IOMMU device IDs, 0 and 7 */
> > > > + master1 {
> > > > + iommus = <&immu1 0 1>, <&immu1 7 1>;
> > > > + };
> > > > +
> > > > + - |
> > > > + /* Example 2 (IOMMU platform device with MSIs) */
> > > > + immu2: iommu@1bcdd000 {
> > > > + compatible = "vendor,chip-iommu", "riscv,iommu";
> > > > + reg = <0x1bccd000 0x1000>;
> > > > + msi-parent = <&imsics_smode>;
> > > > + #iommu-cells = <2>;
> > > > + };
> > > > +
> > > > + bus {
> > > > + #address-cells = <2>;
> > > > + #size-cells = <2>;
> > > > +
> > > > + /* Device with IOMMU device IDs ranging from 32 to 64 */
> > > > + master1 {
> > > > + iommus = <&immu2 32 32>;
> > > > + };
> > > > +
> > > > + pcie@40000000 {
> > > > + compatible = "pci-host-cam-generic";
> > > > + device_type = "pci";
> > > > + #address-cells = <3>;
> > > > + #size-cells = <2>;
> > > > + bus-range = <0x0 0x1>;
> > > > +
> > > > + /* CPU_PHYSICAL(2) SIZE(2) */
> > > > + reg = <0x0 0x40000000 0x0 0x1000000>;
> > > > +
> > > > + /* BUS_ADDRESS(3) CPU_PHYSICAL(2) SIZE(2) */
> > > > + ranges = <0x01000000 0x0 0x01000000 0x0 0x01000000 0x0 0x00010000>,
> > > > + <0x02000000 0x0 0x41000000 0x0 0x41000000 0x0 0x3f000000>;
> > > > +
> > > > + #interrupt-cells = <0x1>;
> > > > +
> > > > + /* PCI_DEVICE(3) INT#(1) CONTROLLER(PHANDLE) CONTROLLER_DATA(2) */
> > > > + interrupt-map = < 0x0 0x0 0x0 0x1 &aplic_smode 0x4 0x1>,
> > > > + < 0x800 0x0 0x0 0x1 &aplic_smode 0x5 0x1>,
> > > > + <0x1000 0x0 0x0 0x1 &aplic_smode 0x6 0x1>,
> > > > + <0x1800 0x0 0x0 0x1 &aplic_smode 0x7 0x1>;
> > > > +
> > > > + /* PCI_DEVICE(3) INT#(1) */
> > > > + interrupt-map-mask = <0xf800 0x0 0x0 0x7>;
> > > > +
> > > > + msi-parent = <&imsics_smode>;
> > > > +
> > > > + /* Devices with bus number 0-127 are mastered via immu2 */
> > > > + iommu-map = <0x0000 &immu2 0x0000 0x8000>;
> > > > + };
> > > > + };
> > > > +...
> > > > --
> > > > 2.34.1
> > > >
> > > >
> > > > _______________________________________________
> > > > linux-riscv mailing list
> > > > linux-riscv@xxxxxxxxxxxxxxxxxxx
> > > > http://lists.infradead.org/mailman/listinfo/linux-riscv

Next message: Jeff Layton: "[PATCH v2] nfsd: inherit required unset default acls from effective set"
Previous message: Leon Romanovsky: "Re: [PATCH v2] IB/hfi1: Use struct_size()"
In reply to: Zong Li: "Re: [PATCH 03/11] dt-bindings: Add RISC-V IOMMU bindings"
Next in thread: Zong Li: "Re: [PATCH 03/11] dt-bindings: Add RISC-V IOMMU bindings"
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