[doc]: Add gnmi feedback design for SmartSwitch

doc/smart-switch/gnmi-feedback/smart-switch-gnmi-feedback-design.md

@@ -0,0 +1,158 @@
+# Smart Switch GNMI feedback design <!-- omit in toc -->
+
+## Table of content <!-- omit in toc -->
+
+- [Revision](#revision)
+- [Overview](#overview)
+- [Requirement](#requirement)
+- [Sequence flow](#sequence-flow)
+  - [Set/Remove](#setremove)
+  - [Message](#message)
+  - [Get](#get)
+  - [Subscribe](#subscribe)
+- [Table](#table)
+  - [APPL STATE DB](#appl-state-db)
+    - [Example 1 DASH\_ROUTE\_TABLE](#example-1-dash_route_table)
+    - [Example 2 DASH\_ROUTING\_APPLIANCE\_TABLE](#example-2-dash_routing_appliance_table)
+
+## Revision
+
+|  Rev  | Date  | Author | Change Description |
+| :---: | :---: | :----: | ------------------ |
+|  0.1  |       | Ze Gan | Initial version.   |
+
+## Overview
+
+The controller communicates with SmartSwitch via the GNMI interface. To enhance configuration efficiency, we provide batch GNMI operations to the GNMI client, allowing it to submit multiple operations in a single request. This document covers two communication channels: the external channel between the GNMI client and server, and the internal channel between the GNMI server and DPU SAI.
+
+## Requirement
+
+- Support for multiple operations in a single request
+- Non-child objects must always include the version ID field
+- The GNMI server supports set, remove, get, and subscribe operations
+- The GNMI client can proactively subscribe to or get objects/tables via object key or table name
+
+| Child object      |
+| ----------------- |
+| DASH_ACL_RULE     |
+| DASH_ROUTE        |
+| DASH_ROUTE_RULE   |
+| DASH_VNET_MAPPING |
+
+
+## Sequence flow
+
+### Set/Remove
+
+```mermaid
+sequenceDiagram
+    participant GC as GNMI Client
+    box NPU SONiC
+        participant GS as GNMI Server
+        participant AD as APP DB
+        participant ASD as APP STATE DB
+    end
+    Note over AD, ASD: DPUx Redis
+    box DPU SONiC
+        participant ZMQ as ZMQ
+        participant SW as SWSS
+        participant SY as SYNCD
+    end
+
+    GC ->> GS: Update commands
+    loop Each commands:
+        GS --) AD: Insert object
+        GS ->> ZMQ: Update command
+    end
+    GS -->> GC: 
+    ZMQ ->> SW: Consume commands
+    SW ->> SY: SAI call
+    SY -->> SW: 
+    alt Set command
+        SW ->> ASD: Update command result
+        Note over ZMQ: Include result code and version ID (If it's non-child object)
+    else Del command
+        SW ->> ASD: Remove objects
+    end
+
+```
+
+### Message
+
+### Get
+
+```mermaid
+sequenceDiagram
+    participant GC as GNMI Client
+    box NPU SONiC
+        participant GS as GNMI Server
+        participant ASD as APP STATE DB
+    end
+    Note over ASD: DPUx Redis
+
+    GC ->> GS: Query object or table result
+    GS ->> ASD: Get object via key or get objects via table name
+    ASD -->> GS: Query results
+    GS -->> GC: Query result
+
+```
+
+### Subscribe
+
+```mermaid
+sequenceDiagram
+    participant GC as GNMI Client
+    box NPU SONiC
+        participant GS as GNMI Server
+        participant ASD as APP STATE DB
+    end
+    Note over ASD: DPUx Redis
+    participant DPU as DPU
+
+    GC ->> GS: Subscribe object or table
+    GS ->> GS: Register subscribe events
+    GS ->> ASD: Get object via key or get objects via table name
+    Note over ASD: Cache result before subscribe
+    ASD -->> GS: Query results
+    GS -->> GC: Query results
+    loop Each commands
+        alt Set command
+            DPU ->> ASD: Update command result
+        else Del command
+            DPU ->> ASD: Remove objects
+        end
+    end
+    ASD -->> GS: Proactively push results
+    GS -->> GC: Proactively push results
+
+```
+
+## Table
+
+### APPL STATE DB
+
+DASH state table in APPL STATE DB, table name is the same as DASH table, key is the same, and fields are result and version ID if it's not a child object.
+
+#### Example 1 DASH_ROUTE_TABLE
+
+```text
+DASH_ROUTE_TABLE:{{group_id}}:{{prefix}}
+    "result": {{result}}
+
+key         = DASH_ROUTE_TABLE:group_id:prefix
+; field     = value
+result      = uint32 0 for success, > 0 for error code
+```
+
+#### Example 2 DASH_ROUTING_APPLIANCE_TABLE
+
+```
+DASH_ROUTE_GROUP_TABLE:{{group_id}}
+    "result": {{result}}
+    "version_id": {{string}}
+
+key         = DASH_ROUTE_GROUP_TABLE:group_id
+; field     = value
+result      = uint32 0 for success, > 0 for error code
+version_id  = string, Indicate the unique version of metadata of route group. E.G. "1", "1.1".
+```