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Date: Fri, 15 Dec 2023 00:27:31 +0300
From: Serge Semin <fancer.lancer@gmail.com>
To: Rob Herring <robh@kernel.org>
Cc: Andrew Lunn <andrew@lunn.ch>, Heiner Kallweit <hkallweit1@gmail.com>, 
	Russell King <linux@armlinux.org.uk>, Alexandre Torgue <alexandre.torgue@foss.st.com>, 
	Jose Abreu <joabreu@synopsys.com>, Jose Abreu <Jose.Abreu@synopsys.com>, 
	Maxime Chevallier <maxime.chevallier@bootlin.com>, Tomer Maimon <tmaimon77@gmail.com>, 
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>, Conor Dooley <conor+dt@kernel.org>, 
	"David S. Miller" <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, 
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>, openbmc@lists.ozlabs.org, 
	netdev@vger.kernel.org, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 08/16] dt-bindings: net: Add Synopsys DW xPCS
 bindings
Message-ID: <52rttyyba6tbklxqv3gif2oyz4ttwlqcaljdkjesb6vaji45pz@46u6t573y7k2>
References: <20231205103559.9605-1-fancer.lancer@gmail.com>
 <20231205103559.9605-9-fancer.lancer@gmail.com>
 <20231214174058.GA624576-robh@kernel.org>
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In-Reply-To: <20231214174058.GA624576-robh@kernel.org>

Hi Rob

On Thu, Dec 14, 2023 at 11:40:58AM -0600, Rob Herring wrote:
> On Tue, Dec 05, 2023 at 01:35:29PM +0300, Serge Semin wrote:
> > Synopsys DesignWare XPCS IP-core is a Physical Coding Sublayer (PCS) layer
> > providing an interface between the Media Access Control (MAC) and Physical
> > Medium Attachment Sublayer (PMA) through a Media independent interface.
> > >From software point of view it exposes IEEE std. Clause 45 CSR space and
> > can be accessible either by MDIO or MCI/APB3 bus interfaces. The later
> > case is described by means of a dedicated DT-bindings which imply having
> > the DW XPCS Management Interface defined as a DT-supernode which child the
> > PCSs nodes would be (in the same way as the standard MDIO buses and
> > devices are normally defined).
> > 
> > Besides of that DW XPCS DT-nodes can have the interrupts and clock source
> > properties specified. The former one indicates the Clause 73/37
> > auto-negotiation events like: negotiation page received, AN is completed
> > or incompatible link partner. The clock DT-properties can describe up to
> > two clock sources: internal one and the one connected to the chip pad.
> > Either of them is supposed to be used as the device reference clocks.
> > 
> > Finally the DW XPCS IP-core can be optionally synthesized with a
> > vendor-specific interface connected to Synopsys PMA (also called
> > DesignWare Consumer/Enterprise PHY). Alas that isn't auto-detectable
> > anyhow so if the DW XPCS device has the respective PMA attached then it
> > should be reflected in the DT-node compatible string so the driver would
> > be aware of the PMA-specific device capabilities (mainly connected with
> > CSRs available for the fine-tunings).
> > 
> > Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
> > ---
> >  .../bindings/net/pcs/snps,dw-xpcs.yaml        | 88 +++++++++++++++++++
> >  .../bindings/net/snps,dw-xpcs-mi.yaml         | 88 +++++++++++++++++++
> >  2 files changed, 176 insertions(+)
> >  create mode 100644 Documentation/devicetree/bindings/net/pcs/snps,dw-xpcs.yaml
> >  create mode 100644 Documentation/devicetree/bindings/net/snps,dw-xpcs-mi.yaml
> > 
> > diff --git a/Documentation/devicetree/bindings/net/pcs/snps,dw-xpcs.yaml b/Documentation/devicetree/bindings/net/pcs/snps,dw-xpcs.yaml
> > new file mode 100644
> > index 000000000000..9694ef51abad
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/pcs/snps,dw-xpcs.yaml
> > @@ -0,0 +1,88 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/net/pcs/snps,dw-xpcs.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Synopsys DesignWare Ethernet PCS
> > +
> > +maintainers:
> > +  - Jose Abreu <Jose.Abreu@synopsys.com>
> > +
> > +description:
> > +  Synopsys DesignWare Ethernet Physical Coding Sublayer provides an interface
> > +  between Media Access Control and Physical Medium Attachment Sublayer through
> > +  the Media Independent Interface (XGMII, USXGMII, XLGMII, GMII, etc)
> > +  controlled by means of the IEEE std. Clause 45 registers set. The PCS can be
> > +  optionally synthesized with a vendor-specific interface connected to
> > +  Synopsys PMA (also called DesignWare Consumer/Enterprise PHY) although in
> > +  general it can be used to communicate with any compatible PHY.
> > +
> > +properties:
> > +  compatible:
> > +    oneOf:
> > +      - description: Synopsys DesignWare XPCS with none or unknown PMA
> > +        const: snps,dw-xpcs
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen1 3G PMA
> > +        const: snps,dw-xpcs-gen1-3g
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen2 3G PMA
> > +        const: snps,dw-xpcs-gen2-3g
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen2 6G PMA
> > +        const: snps,dw-xpcs-gen2-6g
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen4 3G PMA
> > +        const: snps,dw-xpcs-gen4-3g
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen4 6G PMA
> > +        const: snps,dw-xpcs-gen4-6g
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen5 10G PMA
> > +        const: snps,dw-xpcs-gen5-10g
> > +      - description: Synopsys DesignWare XPCS with Consumer Gen5 12G PMA
> > +        const: snps,dw-xpcs-gen5-12g
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    description:
> > +      System interface interrupt output (sbd_intr_o) indicating Clause 73/37
> > +      auto-negotiation events like':' Page received, AN is completed or
> 

> like':' ?

Right. I'll drop it.

> 
> > +      incompatible link partner.
> > +    maxItems: 1
> > +
> > +  clocks:
> > +    description:

> > +      PCS/PMA interface be can clocked either by internal reference clock

s/be can/can be

> > +      source or by an externally connected (via a pad) clock generator.
> > +    minItems: 1
> > +    maxItems: 2
> > +
> > +  clock-names:
> > +    minItems: 1
> > +    maxItems: 2
> > +    items:
> > +      enum: [ core, pad ]
> > +
> > +required:
> > +  - compatible
> > +  - reg
> 

> Don't you always need a clock?

It depends on the PMA nature. Synopsys PHY requires either of the two
clocks: alt/core clock or pad clock. Both of them might be supplied on
a platform though, but only one can be selected at a time. It's done
by means of the Synopsys PHY-specific CSR exposed in the MMD 1
(PMA/PMD). If there is non-Synopsys PHY (PMA) attached then I guess it
can be also clocked somehow, but it will be platform-depended.

> 
> > +
> > +additionalProperties: false
> > +
> > +examples:
> > +  - |
> > +    #include <dt-bindings/interrupt-controller/irq.h>
> > +
> > +    mdio-bus {
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +
> > +      xgmac_pcs: ethernet-pcs@0 {
> > +        compatible = "snps,dw-xpcs";
> > +        reg = <0>;
> > +
> > +        interrupts = <79 IRQ_TYPE_LEVEL_HIGH>;
> > +
> > +        clocks = <&ccu_core>, <&ccu_pad>;
> > +        clock-names = "core", "pad";
> > +      };
> > +    };
> > +...
> > diff --git a/Documentation/devicetree/bindings/net/snps,dw-xpcs-mi.yaml b/Documentation/devicetree/bindings/net/snps,dw-xpcs-mi.yaml
> > new file mode 100644
> > index 000000000000..67ddba9d61fd
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/net/snps,dw-xpcs-mi.yaml
> > @@ -0,0 +1,88 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/net/snps,dw-xpcs-mi.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Synopsys DesignWare Ethernet PCS Management Interface
> > +
> > +maintainers:
> > +  - Serge Semin <fancer.lancer@gmail.com>
> > +
> > +description:
> > +  Synopsys DesignWare Ethernet PCS provides an interface between MAC and PMA
> > +  through the Media Independent Interface. The PCS CSRs can be accessible over
> > +  the Ethernet MDIO bus or directly by means of the APB3/MCI interfaces. In the
> > +  later case the XPCS can be mapped right to the system IO memory space.
> > +
> > +allOf:
> > +  - $ref: mdio.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    const: snps,dw-xpcs-mi
> > +
> > +  reg:
> > +    items:
> > +      - description:
> > +          DW XPCS CSRs space can be either 'directly' or 'indirectly'
> > +          accessible. In the former case all Clause 45 registers are
> > +          contiguously mapped within the address space MMD '[20:16]',
> > +          Reg '[15:0]'. In the later case the space is divided to the
> > +          multiple 256 register sets. There is a special viewport CSR
> > +          which is responsible for the set selection. The upper part of
> > +          the CSR address is supposed to be written in there thus the
> > +          corresponding subset would be mapped over the lowest 255 CSRs.
> > +
> > +  reg-names:
> > +    items:
> > +      - enum: [ direct, indirect ]
> > +
> > +  reg-io-width:
> > +    description:
> > +      The way the CSRs are mapped to the memory is platform depended. Since
> 

> dependent

Ok.

> 
> > +      each Clause 45 CSR is of 16-bits wide the access instructions must be
> > +      two bytes aligned at least.
> > +    default: 2
> > +    enum: [ 2, 4 ]
> > +
> > +  clocks:
> > +    items:
> > +      - description: Peripheral MCI/APB3 bus clock source
> > +
> > +  clock-names:
> > +    items:
> > +      - const: pclk
> > +
> > +patternProperties:
> > +  'ethernet-pcs@[0-9a-f]+$':
> > +    type: object
> > +
> > +    $ref: pcs/snps,dw-xpcs.yaml#
> 

> This causes dw-xpcs to be validated twice. Does this MDIO bus support 
> other devices on it or it is fixed config?

It turned out I was wrong to define the DW XPCS interface as the MDIO
bus. DW XPCS can be synthesized with one of the next management
interfaces:

1. MDIO - normal serial MDIO-bus interface.
2-3. MCI/APB3 - parallel interfaces so the PCS device can be easier
embedded into the system memory bus.

Initially I thought that more than one device can be accessible over
the same MCI/APB3 port with the MS bits being used to reach particular
device. But just recently I discovered that it wasn't correct. The
port_id_i[4:0] input signal isn't present for the MCI or APB3
interface. Thus the DW XPCS device is just a normal memory-mapped
platform device with no such thing like DW XPCS MI above. I'll change
the currently implemented hierarchical device representation from:

mdio@1f05d000 {
	compatible = "snps,dwmac-mi";
	reg = <0 0x1f05d000 0 0x1000>;

	xgmac_pcs: ethernet-pcs@0 {
		compatible = "snps,dw-xpcs";
		reg = <0>;
	};
};
to just a single node:
xgmac_pcs: ethernet-pcs@0 {
	compatible = "snps,dw-xpcs";
	reg = <0 0x1f05d000 0 0x1000>;

	...
};

I pointed that out earlier today in a comment to another patch of this
series:
https://lore.kernel.org/netdev/xhj7jchcv63y2bmnedxqffnmh3fvdxirccdugnnljruemuiurz@ceafs7mivbqp/

-Serge(y)

> 
> > +
> > +required:
> > +  - compatible
> > +  - reg
> > +  - reg-names
> > +
> > +unevaluatedProperties: false
> > +
> > +examples:
> > +  - |
> > +    mdio@1f05d000 {
> > +      compatible = "snps,dw-xpcs-mi";
> > +      reg = <0x1f05d000 0x1000>;
> > +      reg-names = "indirect";
> > +      #address-cells = <1>;
> > +      #size-cells = <0>;
> > +
> > +      clocks = <&ccu_pclk>;
> > +      clock-names = "pclk";
> > +
> > +      reg-io-width = <4>;
> > +
> > +      ethernet-pcs@0 {
> > +        compatible = "snps,dw-xpcs";
> > +        reg = <0>;
> > +      };
> > +    };
> > -- 
> > 2.42.1
> >