[PATCH v7 net-next 01/15] dt-bindings: net: dsa: update the description of 'dsa,member' property

[Wei Fang <wei.fang@nxp.com>]

The current description indicates that the 'dsa,member' property cannot
be set for a switch that is not part of any cluster. Vladimir thinks
that this is a case where the actual technical limitation was poorly
transposed into words when this restriction was first documented, in
commit 8c5ad1d6179d ("net: dsa: Document new binding").

The true technical limitation is that many DSA tagging protocols are
topology-unaware, and always call dsa_conduit_find_user() with a
switch_id of 0. Specifying a custom "dsa,member" property with a
non-zero switch_id would break them.

Therefore, for topology-aware switches, it is fine to specify this
property for them, even if they are not part of any cluster. Our NETC
switch is a good example which is topology-aware, the switch_id is
carried in the switch tag, but the switch_id 0 is reserved for VEPA
switch and cannot be used, so we need to use this property to assign
a non-zero switch_id for it.

Suggested-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Wei Fang <wei.fang@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
---
 Documentation/devicetree/bindings/net/dsa/dsa.yaml | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/net/dsa/dsa.yaml b/Documentation/devicetree/bindings/net/dsa/dsa.yaml
index 2abd036578d1..801e1411e5c2 100644
--- a/Documentation/devicetree/bindings/net/dsa/dsa.yaml
+++ b/Documentation/devicetree/bindings/net/dsa/dsa.yaml
@@ -28,7 +28,11 @@ properties:
       A two element list indicates which DSA cluster, and position within the
       cluster a switch takes. <0 0> is cluster 0, switch 0. <0 1> is cluster 0,
       switch 1. <1 0> is cluster 1, switch 0. A switch not part of any cluster
-      (single device hanging off a CPU port) must not specify this property
+      (single device hanging off a CPU port) does not usually need to specify
+      this property, and then it becomes cluster 0, switch 0. For a topology
+      aware switch, its switch index can be specified through this property,
+      even if it is not part of any cluster. Also, topology-unaware switches
+      must always be defined as index 0 of their cluster.
     $ref: /schemas/types.yaml#/definitions/uint32-array
 
 additionalProperties: true
-- 
2.34.1