[RFC PATCH 2/2] dt-bindings: net: Add mctp-i2c bus-attach property

[Matt Johnston <matt@codeconstruct.com.au>]

Allows attaching multiple child busses in a mux topology
to an mctp-i2c instance on the root bus. In general I2C
slave mode does not make sense for mux busses, but the MCTP
request/response protocol means the the root can switch
between child muxes for incoming I2C messages.

Signed-off-by: Matt Johnston <matt@codeconstruct.com.au>
---
 .../devicetree/bindings/net/mctp-i2c.yaml     | 42 +++++++++++++++++--
 1 file changed, 38 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/net/mctp-i2c.yaml b/Documentation/devicetree/bindings/net/mctp-i2c.yaml
index f9378cd845d4..45429cbcc6a1 100644
--- a/Documentation/devicetree/bindings/net/mctp-i2c.yaml
+++ b/Documentation/devicetree/bindings/net/mctp-i2c.yaml
@@ -12,11 +12,10 @@ maintainers:
 description:
   The MCTP I2C binding defines an MCTP endpoint on the I2C bus to
   communicate with I2C peripherals using MCTP (DMTF specification DSP0237).
-
-  An mctp-i2c device must be attached to a hardware bus adapter which supports
+  A single binding node can attach to multiple child busses in a mux topology.
+  An mctp-i2c node's parent must be a hardware bus adapter which supports
   slave functionality. The reg address must include I2C_OWN_SLAVE_ADDRESS.
 
-
 properties:
   compatible:
     const: mctp-i2c
@@ -24,6 +23,17 @@ properties:
   reg:
     maxItems: 1
 
+  bus-attach:
+    $ref: "/schemas/types.yaml#/definitions/phandle-array"
+    description: |
+      List of phandles of I2C busses to attach to. I2C mux busses may only
+      be attached to an mctp-i2c binding on their parent root adapter in the
+      mux topology.
+      If no bus-attach property is specified then only the direct parent
+      I2C bus is attached. Otherwise to include a direct parent bus it
+      must be included in the bus-attach list if needed.
+
+
 additionalProperties: true
 
 required:
@@ -33,12 +43,36 @@ required:
 examples:
   - |
     #include <dt-bindings/i2c/i2c.h>
-    i2c {
+
+    // simple attaching to a root adapter i2c0
+    i2c0: i2cbus0 {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        mctp@50 {
+            compatible = "mctp-i2c";
+            reg = <(0x50 | I2C_OWN_SLAVE_ADDRESS)>;
+        };
+    };
+
+    // attaching to a root adapter i2c5 and a child mux bus i2c14
+    i2c5: i2cbus5 {
         #address-cells = <1>;
         #size-cells = <0>;
 
         mctp@50 {
             compatible = "mctp-i2c";
             reg = <(0x50 | I2C_OWN_SLAVE_ADDRESS)>;
+            attach-bus = <&i2c5 &i2c14>;
         };
     };
+
+    i2cmux0 {
+      compatible = "i2c-mux-gpio";
+      #address-cells = <1>;
+      #size-cells = <0>;
+      i2c-parent = <&i2c0>;
+      i2c14: i2c@5 {
+        reg = <0>;
+      };
+    };
-- 
2.30.2