dt-bindings: memory: Add jedec,lpddrX-channel binding

This patch adds a new device tree binding for an LPDDR channel to serve
as a top-level organizing node for LPDDR part nodes nested below it. An
LPDDR channel needs to have an "io-width" property to describe its width
(this is important because this width does not always match the io-width
of the part number, indicating that multiple parts are wired in parallel
on the same channel), as well as one or more nested "rank@X" nodes.
Those represent information about the individual ranks of each LPDDR
part connected on that channel and should match the existing
"jedec,lpddrX" bindings for individual LPDDR parts.

New platforms should be using this node -- the existing practice of
providing a raw, toplevel "jedec,lpddrX" node without indication of how
many identical parts are in the system should be considered deprecated.

Signed-off-by: Julius Werner <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Krzysztof Kozlowski <[e-mail]>

Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr-channel.yaml

···
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/memory-controllers/ddr/jedec,lpddr-channel.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: LPDDR channel with chip/rank topology description
+
+description:
+  An LPDDR channel is a completely independent set of LPDDR pins (DQ, CA, CS,
+  CK, etc.) that connect one or more LPDDR chips to a host system. The main
+  purpose of this node is to overall LPDDR topology of the system, including the
+  amount of individual LPDDR chips and the ranks per chip.
+
+maintainers:
+  - Julius Werner <[e-mail]>
+
+properties:
+  compatible:
+    enum:
+      - jedec,lpddr2-channel
+      - jedec,lpddr3-channel
+      - jedec,lpddr4-channel
+      - jedec,lpddr5-channel
+
+  io-width:
+    description:
+      The number of DQ pins in the channel. If this number is different
+      from (a multiple of) the io-width of the LPDDR chip, that means that
+      multiple instances of that type of chip are wired in parallel on this
+      channel (with the channel's DQ pins split up between the different
+      chips, and the CA, CS, etc. pins of the different chips all shorted
+      together).  This means that the total physical memory controlled by a
+      channel is equal to the sum of the densities of each rank on the
+      connected LPDDR chip, times the io-width of the channel divided by
+      the io-width of the LPDDR chip.
+    enum:
+      - 8
+      - 16
+      - 32
+      - 64
+      - 128
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^rank@[0-9]+$":
+    type: object
+    description:
+      Each physical LPDDR chip may have one or more ranks. Ranks are
+      internal but fully independent sub-units of the chip. Each LPDDR bus
+      transaction on the channel targets exactly one rank, based on the
+      state of the CS pins. Different ranks may have different densities and
+      timing requirements.
+    required:
+      - reg
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: jedec,lpddr2-channel
+    then:
+      patternProperties:
+        "^rank@[0-9]+$":
+          $ref: /schemas/memory-controllers/ddr/jedec,lpddr2.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: jedec,lpddr3-channel
+    then:
+      patternProperties:
+        "^rank@[0-9]+$":
+          $ref: /schemas/memory-controllers/ddr/jedec,lpddr3.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: jedec,lpddr4-channel
+    then:
+      patternProperties:
+        "^rank@[0-9]+$":
+          $ref: /schemas/memory-controllers/ddr/jedec,lpddr4.yaml#
+  - if:
+      properties:
+        compatible:
+          contains:
+            const: jedec,lpddr5-channel
+    then:
+      patternProperties:
+        "^rank@[0-9]+$":
+          $ref: /schemas/memory-controllers/ddr/jedec,lpddr5.yaml#
+
+required:
+  - compatible
+  - io-width
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    lpddr-channel0 {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      compatible = "jedec,lpddr3-channel";
+      io-width = <32>;
+
+      rank@0 {
+        compatible = "lpddr3-ff,0100", "jedec,lpddr3";
+        reg = <0>;
+        density = <8192>;
+        io-width = <16>;
+        revision-id = <1 0>;
+      };
+    };
+
+    lpddr-channel1 {
+      #address-cells = <1>;
+      #size-cells = <0>;
+      compatible = "jedec,lpddr4-channel";
+      io-width = <32>;
+
+      rank@0 {
+        compatible = "lpddr4-05,0301", "jedec,lpddr4";
+        reg = <0>;
+        density = <4096>;
+        io-width = <32>;
+        revision-id = <3 1>;
+      };
+
+      rank@1 {
+        compatible = "lpddr4-05,0301", "jedec,lpddr4";
+        reg = <1>;
+        density = <2048>;
+        io-width = <32>;
+        revision-id = <3 1>;
+      };
+    };

Documentation/devicetree/bindings/memory-controllers/ddr/jedec,lpddr-props.yaml

···
 description:
   Different LPDDR types generally use the same properties and only differ in the
   range of legal values for each. This file defines the common parts that can be
-  reused for each type.
+  reused for each type. Nodes using this schema should generally be nested under
+  an LPDDR channel node.
 
 maintainers:
   - Krzysztof Kozlowski <[e-mail]>
···
       formatted in lower case hexadecimal representation with leading zeroes.
       The latter form can be useful when LPDDR nodes are created at runtime by
       boot firmware that doesn't have access to static part number information.
+
+  reg:
+    description:
+      The rank number of this LPDDR rank when used as a subnode to an LPDDR
+      channel.
+    minimum: 0
+    maximum: 3
 
   revision-id:
     $ref: /schemas/types.yaml#/definitions/uint32-array