Re: [PATCH 1/2] dt-bindings: pci: Add DT bindings for apple,pcie

[Mark Kettenis <mark.kettenis@xs4all.nl>]

> From: Rob Herring <robh+dt@kernel.org>
> Date: Mon, 17 May 2021 09:16:49 -0500

Hi Rob,

Thanks for taking a look.  Below are some further explanations and
questions.  I'll probably wait to collect a bit more feedback before
re-rolling this series.

> On Sun, May 16, 2021 at 4:19 PM Mark Kettenis <mark.kettenis@xs4all.nl> wrote:
> >
> > From: Mark Kettenis <kettenis@openbsd.org>
> >
> > The Apple PCIe host controller is a PCIe host controller with
> > multiple root ports present in Apple ARM SoC platforms, including
> > various iPhone and iPad devices and the "Apple Silicon" Macs.
> 
> All the cover letter will be lost in the git history. Please mention
> some details like this is a DWC controller here. I disagree that you
> can't use the DWC binding. You can use it and extend it with what's
> needed here. And that way, we could move from generic ECAM to an
> actual driver in the OS if needed (hopefully not). More below.

Should I mention the DWC heritage in the description of the device in
the DT schema or in the commit message of the schema?  Or both?

Note that it looks as if Apple has replaced most of the DWC logic in
the controller with their own logic.  The DWC ATU isn't there, not in
its original form nor in its newer "unrolled" form.  The MSI logic is
Apple's own as well.  As such, none of the properties specified in
Documentation/devicetree/bindings/pci/designware-pcie.txt that aren't
specified by /schemas/pci/pci-bus.yaml apply.  That said, the binding
doesn't deliberately deviate from the DWC binding either.

> > Signed-off-by: Mark Kettenis <kettenis@openbsd.org>
> > ---
> >  .../devicetree/bindings/pci/apple,pcie.yaml   | 150 ++++++++++++++++++
> >  MAINTAINERS                                   |   1 +
> >  2 files changed, 151 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pci/apple,pcie.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/pci/apple,pcie.yaml b/Documentation/devicetree/bindings/pci/apple,pcie.yaml
> > new file mode 100644
> > index 000000000000..af3c9f64e380
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pci/apple,pcie.yaml
> > @@ -0,0 +1,150 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/pci/apple,pcie.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Apple PCIe host controller
> > +
> > +maintainers:
> > +  - Mark Kettenis <kettenis@openbsd.org>
> > +
> > +description: |
> > +  The Apple PCIe host controller is a PCIe host controller with
> > +  multiple root ports present in Apple ARM SoC platforms, including
> > +  various iPhone and iPad devices and the "Apple Silicon" Macs.
> > +
> > +allOf:
> > +  - $ref: /schemas/pci/pci-bus.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    items:
> > +      - const: apple,t8103-pcie
> > +      - const: apple,pcie
> > +
> > +  reg:
> > +    minItems: 4
> > +    maxItems: 6
> 
> 6 or...
> 
> > +  reg-names:
> > +    minItems: 4
> > +    maxItems: 7
> 
> 7?

Oops.  That is a leftover from when I was checking whether the schema
would catch certain errors in the dts files.

> > +    items:
> > +      - const: ecam
> 
> 'config'
> 
> The difference between ECAM or not in existing devices is really just
> the size. If you look at the addresses on other DWC bindings, the
> config region is just an iATU window within the host's PCI address
> range.

If 'config' is a better name, sure, I can change that.  I don't think
the config region is just a window into the host's PCI address range
though as config space requires a nGnRnE mapping whereas the PCI
address range requires a nGnRE mapping.  That's what the
"nonposted-mmio" discussion was all about.

> > +      - const: rc
> 
> This would be 'dbi'?

I don't think so.  As far as I can determine this registers block
contains only Apple-specific registers and none of the registers that
live in "Designware DBI space" on other hardware.

> Also check if we need 'atu' (only if it's not at the default offset)?

As far as I can tell there is no Designware ATU on the Apple hardware.

> > +      - const: phy
> 
> Should there be a separate phy node?

At this point neither the U-Boot driver nor the OpenBSD driver access
registers in this block.  Should I leave it out for now?

> > +      - const: port0
> > +      - const: port1
> > +      - const: port2
> 
> What's in these registers?

This block contains registers that are per-port.  This includes the
Apple-specific link control registers, the Apple-specific MSI
registers, PCI requestor ID to IOMMU stream ID mapping registers.

> > +
> > +  ranges:
> > +    minItems: 2
> > +    maxItems: 2
> > +
> > +  interrupts:
> > +    minItems: 3
> > +    maxItems: 3
> 
> Need to define what each one is.

Hmm, haven't figured that out yet.  U-Boot doesn't need them and
neither does my OpenBSD driver.  Should I leave these out for now?

> > +
> > +  msi-ranges:
> > +    description:
> > +      A list of pairs <intid span>, where "intid" is the first
> > +      interrupt number that can be used as an MSI, and "span" the size
> > +      of that range.
> 
> Hopefully, Marc Z will comment on the MSI bits. msi-map doesn't work
> here? If we need something else, then it should be added to
> pci-msi.txt.

This was actually based on discussions I had with Marc on #asahilinux
some time ago.  But certainly something that we need his blessing on
;).

> One problem with this is it assumes 'intid' is one cell. It's really 2
> for the AIC if we ignore flags (which would be another assumption that
> we can ignore the last cell). Or maybe this belongs in the AIC
> binding?

The MSI translation defenitely happens in the PCIe host bridge.  The
MSI target address is programmed in a per-port register and not
translated by the IOMMU.

> 
> > +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> > +    items:
> > +      minItems: 2
> > +      maxItems: 2
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - reg-names
> > +  - bus-range
> > +  - interrupts
> > +  - msi-controller
> > +  - msi-parent
> > +  - msi-ranges
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/interrupt-controller/apple-aic.h>
> > +    #include <dt-bindings/pinctrl/apple.h>
> > +
> > +    soc {
> > +      #address-cells = <2>;
> > +      #size-cells = <2>;
> > +
> > +      pcie0: pcie@690000000 {
> > +        compatible = "apple,t8103-pcie", "apple,pcie";
> > +        device_type = "pci";
> > +
> > +        reg = <0x6 0x90000000 0x0 0x1000000>,
> > +              <0x6 0x80000000 0x0 0x4000>,
> > +              <0x6 0x8c000000 0x0 0x4000>,
> > +              <0x6 0x81000000 0x0 0x8000>,
> > +              <0x6 0x82000000 0x0 0x8000>,
> > +              <0x6 0x83000000 0x0 0x8000>;
> > +        reg-names = "ecam", "rc", "phy", "port0", "port1", "port2";
> > +
> > +        interrupt-parent = <&aic>;
> > +        interrupts = <AIC_IRQ 695 IRQ_TYPE_LEVEL_HIGH>,
> > +                     <AIC_IRQ 698 IRQ_TYPE_LEVEL_HIGH>,
> > +                     <AIC_IRQ 701 IRQ_TYPE_LEVEL_HIGH>;
> > +
> > +        msi-controller;
> > +        msi-parent = <&pcie0>;
> > +        msi-ranges = <704 32>;
> > +
> > +        iommu-map = <0x0 &dart0 0x8000 0x100>,
> > +                    <0x100 &dart0 0x100 0x100>,
> > +                    <0x200 &dart1 0x200 0x100>,
> > +                    <0x300 &dart2 0x300 0x100>;
> > +        iommu-map-mask = <0xff00>;
> 
> These need to be documented. You can assume they have a type already,
> so just 'true' or any constraints.

No examples of that yet, but I can try to get that right...

> > +
> > +        bus-range = <0 7>;
> > +        #address-cells = <3>;
> > +        #size-cells = <2>;
> > +        ranges = <0x43000000 0x6 0xa0000000 0x6 0xa0000000 0x0 0x20000000>,
> > +                 <0x02000000 0x0 0xc0000000 0x6 0xc0000000 0x0 0x40000000>;
> > +
> > +        clocks = <&pcie_core_clk>, <&pcie_aux_clk>, <&pcie_ref_clk>;
> > +        pinctrl-0 = <&pcie_pins>;
> > +        pinctrl-names = "default";
> > +
> > +        pci@0,0 {
> > +          device_type = "pci";
> > +          reg = <0x0 0x0 0x0 0x0 0x0>;
> > +          reset-gpios = <&pinctrl_ap 152 0>;
> > +          max-link-speed = <2>;
> > +
> > +          #address-cells = <3>;
> > +          #size-cells = <2>;
> > +          ranges;
> > +        };
> > +
> > +        pci@1,0 {
> > +          device_type = "pci";
> > +          reg = <0x800 0x0 0x0 0x0 0x0>;
> > +          reset-gpios = <&pinctrl_ap 153 0>;
> > +          max-link-speed = <2>;
> > +
> > +          #address-cells = <3>;
> > +          #size-cells = <2>;
> > +          ranges;
> > +        };
> > +
> > +        pci@2,0 {
> > +          device_type = "pci";
> > +          reg = <0x1000 0x0 0x0 0x0 0x0>;
> > +          reset-gpios = <&pinctrl_ap 33 0>;
> > +          max-link-speed = <1>;
> > +
> > +          #address-cells = <3>;
> > +          #size-cells = <2>;
> > +          ranges;
> > +        };
> > +      };
> > +    };
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 7327c9b778f1..789d79315485 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -1654,6 +1654,7 @@ C:        irc://chat.freenode.net/asahi-dev
> >  T:     git https://github.com/AsahiLinux/linux.git
> >  F:     Documentation/devicetree/bindings/arm/apple.yaml
> >  F:     Documentation/devicetree/bindings/interrupt-controller/apple,aic.yaml
> > +F:     Documentation/devicetree/bindings/pci/apple,pcie.yaml
> >  F:     Documentation/devicetree/bindings/pinctrl/apple,pinctrl.yaml
> >  F:     arch/arm64/boot/dts/apple/
> >  F:     drivers/irqchip/irq-apple-aic.c
> > --
> > 2.31.1
> >
> 

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