dt-bindings: net: Add Synopsys DW xPCS bindings

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. In the former
case the PCS device is supposed to be defined under the respective MDIO
bus DT-node. In the later case the DW xPCS will be just a normal IO
memory-mapped device.

Besides of that DW XPCS DT-nodes can have an interrupt signal 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
three clock sources: peripheral bus clock source, internal reference clock
and the externally connected reference clock.

Finally the DW XPCS IP-core can be optionally synthesized with a
vendor-specific interface connected to the Synopsys PMA (also called
DesignWare Consumer/Enterprise PHY). Alas that isn't auto-detectable in a
portable way. 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>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/pcs/snps,dw-xpcs.yaml

+# 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:
+  - Serge Semin <fancer.lancer@gmail.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.
+
+  The PCS CSRs can be accessible either 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.
+
+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:
+    items:
+      - description:
+          In case of the MDIO management interface this just a 5-bits ID
+          of the MDIO bus device. If DW XPCS CSRs space is accessed over the
+          MCI or APB3 management interfaces, then the space mapping can be
+          either 'direct' or 'indirect'. 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 MMD+REG[20:8] is supposed to be written in there
+          so the corresponding subset would be mapped to 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
+      each Clause 45 CSR is of 16-bits wide the access instructions must be
+      two bytes aligned at least.
+    default: 2
+    enum: [ 2, 4 ]
+
+  interrupts:
+    description:
+      System interface interrupt output (sbd_intr_o) indicating Clause 73/37
+      auto-negotiation events':' Page received, AN is completed or incompatible
+      link partner.
+    maxItems: 1
+
+  clocks:
+    description:
+      The MCI and APB3 interfaces are supposed to be equipped with a clock
+      source connected to the clk_csr_i line.
+
+      PCS/PMA layer can be clocked by an internal reference clock source
+      (phyN_core_refclk) or by an externally connected (phyN_pad_refclk) clock
+      generator. Both clocks can be supplied at a time.
+    minItems: 1
+    maxItems: 3
+
+  clock-names:
+    oneOf:
+      - minItems: 1
+        items: # MDIO
+          - enum: [core, pad]
+          - const: pad
+      - minItems: 1
+        items: # MCI or APB
+          - const: csr
+          - enum: [core, pad]
+          - const: pad
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/interrupt-controller/irq.h>
+
+    ethernet-pcs@1f05d000 {
+      compatible = "snps,dw-xpcs";
+      reg = <0x1f05d000 0x1000>;
+      reg-names = "indirect";
+
+      reg-io-width = <4>;
+
+      interrupts = <79 IRQ_TYPE_LEVEL_HIGH>;
+
+      clocks = <&ccu_pclk>, <&ccu_core>, <&ccu_pad>;
+      clock-names = "csr", "core", "pad";
+    };
+  - |
+    mdio-bus {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      ethernet-pcs@0 {
+        compatible = "snps,dw-xpcs";
+        reg = <0>;
+
+        clocks = <&ccu_core>, <&ccu_pad>;
+        clock-names = "core", "pad";
+      };
+    };
+...