diff --git a/doc/smart-switch/pmon/images/dpu-reboot-seq.mmd b/doc/smart-switch/pmon/images/dpu-reboot-seq.mmd
new file mode 100644
index 00000000000..a3dee89fd89
--- /dev/null
+++ b/doc/smart-switch/pmon/images/dpu-reboot-seq.mmd
@@ -0,0 +1,56 @@
+%%{init: {
+ "theme": "default",
+ "themeVariables": {
+ "actorBkg": "#eaeaea",
+ "actorBorder": "#666",
+ "actorTextColor": "#333",
+ "actorLineColor": "#999",
+ "signalColor": "#333",
+ "signalTextColor": "#333",
+ "labelBoxBkgColor": "#eaeaea",
+ "labelBoxBorderColor": "#666",
+ "labelTextColor": "#333",
+ "loopTextColor": "#333",
+ "activationBkgColor": "#f4f4f4",
+ "activationBorderColor": "#666",
+ "noteBkgColor": "#fff5ad",
+ "noteBorderColor": "#aaaa33",
+ "noteTextColor": "#333"
+ }
+}}%%
+
+sequenceDiagram
+ actor User
+ participant HostService as NPU: host-service
+ participant StateDB as NPU: stateDB
+ participant DpuChassisd as DPU: chassisd
+ participant ChassisStateDB as NPU: chassisStateDB
+ participant Chassisd as NPU: chassisd
+ participant PlatformAPI as NPU: platform API
+
+ User->>HostService: Input: PowerOn or Reboot config or CLI
+ HostService->>HostService: determine-reboot-cause
+ HostService->>HostService: update-reboot-cause
+ activate HostService
+ HostService->>StateDB: update-reboot-cause
+ HostService->>ChassisStateDB: update-reboot-cause
+ HostService->>HostService: end processing
+ deactivate HostService
+
+ DpuChassisd->>ChassisStateDB: publish current boot_id when reachable
+ ChassisStateDB-->>Chassisd: boot_id appears or changes
+ activate Chassisd
+ Chassisd->>Chassisd: compare with persisted boot_id
+
+ alt boot_id differs or no valid baseline exists
+ Chassisd->>PlatformAPI: get-reboot-cause
+ activate PlatformAPI
+ PlatformAPI-->>Chassisd: reboot-cause
+ deactivate PlatformAPI
+ Chassisd->>Chassisd: persist history record with boot_id
+ Chassisd->>ChassisStateDB: refresh REBOOT_CAUSE entries
+ else boot_id is unchanged
+ Chassisd->>Chassisd: no new record
+ end
+
+ deactivate Chassisd
diff --git a/doc/smart-switch/pmon/images/dpu-reboot-seq.svg b/doc/smart-switch/pmon/images/dpu-reboot-seq.svg
index 8182562f926..17759bc53e6 100644
--- a/doc/smart-switch/pmon/images/dpu-reboot-seq.svg
+++ b/doc/smart-switch/pmon/images/dpu-reboot-seq.svg
@@ -1 +1 @@
-
\ No newline at end of file
+
\ No newline at end of file
diff --git a/doc/smart-switch/pmon/smartswitch-pmon.md b/doc/smart-switch/pmon/smartswitch-pmon.md
index b26e5d021be..d53760e8e9b 100644
--- a/doc/smart-switch/pmon/smartswitch-pmon.md
+++ b/doc/smart-switch/pmon/smartswitch-pmon.md
@@ -8,6 +8,7 @@
| 0.4 | 06/06/2024 | Ramesh Raghupathy | Added schema for DPU health-info and called out phase:1 and phase:2 activities for DPU health-info. Added key suffix to module reboot-cause to avoid key conflicts |
| 0.5 | 04/30/2025 | Gagan Punathil Ellath | Added Post Startup and Pre shutdown sections for DPU |
| 0.6 | 06/12/2025 | Gagan Punathil Ellath | DPU State Management Implementation |
+| 0.7 | 06/11/2026 | Charles Tsai | Updated DPU reboot-cause and midplane-down reason |
## Definitions / Abbreviations
@@ -614,9 +615,10 @@ The smartswitch needs to know the reboot cause for the NPU and the DPUs.
```
#### DPU Reboot Cause
* The smartswitch needs to know the reboot cause for all the DPUs.
-* The NPU hardware should be capable of providing the DPU reboot-cause even when the DPUs are dead.
+* The reboot-cause can be captured by the platforms at the appropriate time. The reboot-cause should be reported only when the midplane of DPU transitions to online by calling the `get_reboot_cause` API.
+* Each DPU SONiC publishes a `boot_id` (a fresh UUID generated per boot from `/proc/sys/kernel/random/boot_id`) into its `DPU_STATE` entry in CHASSIS_STATE_DB. The NPU chassisd compares the reported `boot_id` against the last `boot_id` it persisted; when they differ, the NPU chassisd calls `get_reboot_cause()`, writes a history record containing the cause and the `boot_id`, and then refreshes the `REBOOT_CAUSE` entries in CHASSIS_STATE_DB from those records. A changed `boot_id` can only become visible on the NPU once the DPU is reachable and able to write into the NPU's CHASSIS_STATE_DB, so the reported reboot-cause is naturally aligned with the midplane coming online.
* The get_reboot_cause will return the current reboot-cause of the module.
-* For persistent storage of the DPU reboot-cause and reboot-cause-history files use the existing mechanism and host storage path under "/host/reboot-cause/module/dpux".
+* Persistent DPU reboot-cause records are stored under `/host/reboot-cause/module/dpux/history/`, and each record includes the `boot_id`. The `previous-reboot-cause.json` symlink identifies the latest record and provides the persisted `boot_id` baseline. Unlike the NPU workflow, DPU capture does not use `module/dpux/reboot-cause.txt`.
* The storage and retrieval of the reboot-cause of the Switch and PDUs are shown in the sequence diagram
@@ -625,12 +627,9 @@ The smartswitch needs to know the reboot cause for the NPU and the DPUs.
* The switch boots up. Determines the NPU reboot cause.
* Processes the previously stored NPU and DPU reboot-cause files and history files.
* A maximum of ten reboot-cause history entries per dpu will be persisted just like the npu.
-* Updates the NPU reboot-cause into the StateDB and the DPU reboot-cause into the ChassisStateDB.
+* The reboot-cause service (`process-reboot-cause`) updates the NPU reboot-cause in StateDB and rebuilds the DPU `REBOOT_CAUSE|DPUx|
