Re: [PATCH 02/16] dt-bindings: PCI: dwc: Add Baikal-T1 PCIe Root Port bindings

[Serge Semin <fancer.lancer@gmail.com>]

On Mon, Mar 28, 2022 at 06:20:03PM -0500, Rob Herring wrote:
> On Thu, Mar 24, 2022 at 04:37:20AM +0300, Serge Semin wrote:
> > Baikal-T1 SoC is equipped with DWC PCIe v4.60a Root Port controller, which
> > link can be trained to work on up to Gen.3 speed over up to x4 lanes. The
> > controller is supposed to be fed up with four clock sources: DBI
> > peripheral clock, AXI application Tx/Rx clocks and external PHY/core
> > reference clock generating the 100MHz signal. In addition to that the
> > platform provide a way to reset each part of the controller:
> > sticky/non-sticky bits, host controller core, PIPE interface, PCS/PHY and
> > Hot/Power reset signal. The Root Port controller is equipped with multiple
> > IRQ lines like MSI, system AER, PME, HP, Bandwidth change, Link
> > equalization request and eDMA ones. The registers space is accessed over
> > the DBI interface. There can be no more than four inbound or outbound iATU
> > windows configured.
> > 
> > Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
> > 
> > ---
> > 
> > Rob, this DT-bindings most likely will fail the dt_bindings_check
> > evaluations with the "'*' is not of type 'array'" errors for the same
> > reason described in the previous patch. Let's discuss the problem there.
> > ---
> >  .../bindings/pci/baikal,bt1-pcie.yaml         | 148 ++++++++++++++++++
> >  1 file changed, 148 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/pci/baikal,bt1-pcie.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/pci/baikal,bt1-pcie.yaml b/Documentation/devicetree/bindings/pci/baikal,bt1-pcie.yaml
> > new file mode 100644
> > index 000000000000..f34438330a86
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/pci/baikal,bt1-pcie.yaml
> > @@ -0,0 +1,148 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/pci/baikal,bt1-pcie.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Baikal-T1 PCIe Root Port Controller
> > +
> > +maintainers:
> > +  - Serge Semin <fancer.lancer@gmail.com>
> > +
> > +description: |
> > +  Embedded into Baikal-T1 SoC Root Complex controller. It's based on the
> > +  DWC RC PCIe v4.60a IP-core, which is configured to have just a single Root
> > +  Port function and is capable of establishing the link up to Gen.3 speed
> > +  on x4 lanes. It doesn't have embedded clock and reset control module, so
> > +  the proper interface initialization is supposed to be performed by software.
> > +
> > +allOf:
> > +  - $ref: /schemas/pci/pci-bus.yaml#
> > +  - $ref: snps,dw-pcie.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    contains:
> > +      const: baikal,bt1-pcie
> > +
> > +  reg:
> > +    description:
> > +      DBI, DBI2 and at least 4KB outbound iATU-capable region are available.
> 

> outbound iATU-capable region? While configured with iATU, it's just 
> config space from a binding standpoint.

In this particular device the config-space is supposed to be mapped
over the outbound iATU region. It's a MMIO region mapped to the Source
side of the outbound iATU interface.

> 
> It's a bit more precise to do this:
> 
> items:
>   - description: DBI...
>   - description: DBI2...
>   - ...

I know, but I prefer using the reg-names property for that, while
having the 'reg' property with minItems/maxItems constraints specified.
In this case the reg property would be left unordered.

> 
> 
> > +    maxItems: 3
> 
> And then drop this.
> 
> > +
> > +  reg-names:
> > +    minItems: 3
> > +    maxItems: 3
> > +    items:
> > +      enum: [ dbi, dbi2, config ]
> 

> To enforce the order:
> 
> items:
>   - const: dbi
>   - const: dbi2
>   - const: config

Could you please explain why do you always suggest to define the ordered
X/X-names properties group? I just don't see much benefits in such
approach except that it's a bit more readable and one line shorter.

> 
> > +
> > +  interrupts:
> > +    description:
> > +      MSI, AER, PME, Hot-plug, Link Bandwidth Management, Link Equalization
> > +      request and eight Read/Write eDMA IRQ lines are available.
> > +    maxItems: 14
> > +
> > +  interrupt-names:
> > +    minItems: 14
> > +    maxItems: 14
> > +    items:
> > +      oneOf:
> > +        - pattern: '^dma[0-7]$'
> > +        - enum: [ msi, aer, pme, hp, bw_mg, l_eq ]
> 

> Can't you define the order?

Please, see my question in the previous comment.

> 
> > +
> > +  clocks:
> > +    description:
> > +      DBI (attached to the APB bus), AXI-bus master and slave interfaces
> > +      are fed up by the dedicated application clocks. A common reference
> > +      clock signal is supposed to be attached to the corresponding Ref-pad
> > +      of the SoC. It will be redistributed amongst the controller core
> > +      sub-modules (pipe, core, aux, etc).
> > +    minItems: 4
> > +    maxItems: 4
> > +
> > +  clock-names:
> > +    minItems: 4
> > +    maxItems: 4
> > +    items:
> > +      enum: [ dbi, mstr, slv, ref ]
> > +
> > +  resets:
> > +    description:
> > +      A comprehensive controller reset logic is supposed to be implemented
> > +      by software, so almost all the possible application and core reset
> > +      signals are exposed via the system CCU module.
> > +    minItems: 9
> > +    maxItems: 9
> > +
> > +  reset-names:
> > +    minItems: 9
> > +    maxItems: 9
> > +    items:
> > +      enum: [ mstr, slv, pwr, hot, phy, core, pipe, sticky, non-sticky ]
> 

> Again, define the order.

Could you tell me why it's better than unordered property? Really I
don't see good reason enough to define more constraints than required.

> 
> > +
> > +  syscon:
> 

> Needs a vendor prefix.

Ok.

> 
> > +    $ref: /schemas/types.yaml#/definitions/phandle
> > +    description:
> > +      Phandle to the Baikal-T1 System Controller DT node. It's required to
> > +      access some additional PM, Reset-related and LTSSM signals.
> > +
> > +  num-lanes:
> > +    maximum: 4
> > +
> > +  max-link-speed:
> > +    maximum: 3
> > +
> 
> > +  num-ob-windows:
> > +    const: 4
> > +
> > +  num-ib-windows:
> > +    const: 4
> 

> These are deprecated. The driver probes for how many now.

I know that they are deprecated. But they are deprecated on the DT
node level, not in the DT schema. Here by explicitly defining these
properties I signify that there are four in- and outbound iATU
windows. Doesn't that better describe our hardware?

-Sergey

> 
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - reg-names
> > +  - interrupts
> > +  - interrupt-names
> > +  - clocks
> > +  - clock-names
> > +  - resets
> > +  - reset-names
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > +  - |
> > +    pcie@1f052000 {
> > +      compatible = "baikal,bt1-pcie", "snps,dw-pcie-4.60a", "snps,dw-pcie";
> > +      device_type = "pci";
> > +      reg = <0x1f052000 0x1000>, <0x1f053000 0x1000>, <0x1bdbf000 0x1000>;
> > +      reg-names = "dbi", "dbi2", "config";
> > +      #address-cells = <3>;
> > +      #size-cells = <2>;
> > +      ranges = <0x81000000 0 0x00000000 0x1bdb0000 0 0x00008000>,
> > +               <0x82000000 0 0x20000000 0x08000000 0 0x13db0000>;
> > +      bus-range = <0x0 0xff>;
> > +
> > +      interrupts = <0 80 4>, <0 81 4>, <0 82 4>, <0 83 4>,
> > +                   <0 84 4>, <0 85 4>, <0 86 4>, <0 87 4>,
> > +                   <0 88 4>, <0 89 4>, <0 90 4>, <0 91 4>,
> > +                   <0 92 4>, <0 93 4>;
> > +      interrupt-names = "dma0", "dma1", "dma2", "dma3", "dma4", "dma5", "dma6",
> > +                        "dma7", "msi", "aer", "pme", "hp", "bw_mg", "l_eq";
> > +
> > +      clocks = <&ccu_sys 1>, <&ccu_axi 6>, <&ccu_axi 7>, <&clk_pcie>;
> > +      clock-names = "dbi", "mstr", "slv", "ref";
> > +
> > +      resets = <&ccu_axi 6>, <&ccu_axi 7>, <&ccu_sys 7>, <&ccu_sys 10>,
> > +               <&ccu_sys 4>, <&ccu_sys 6>, <&ccu_sys 5>, <&ccu_sys 8>,
> > +               <&ccu_sys 9>;
> > +      reset-names = "mstr", "slv", "pwr", "hot", "phy", "core", "pipe",
> > +                    "sticky", "non-sticky";
> > +
> > +      reset-gpios = <&port0 0 1>;
> > +
> > +      num-lanes = <4>;
> > +      max-link-speed = <3>;
> > +    };
> > +...
> > -- 
> > 2.35.1
> > 
> >