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+# BMC Boot Cause Event Log
+
+Author: Patrick Lin (patrick_lin_wiwynn)
+
+Other contributors: Delphine Chiu(delphinechiu), Bonnie Lo(bonnielo), Ricky
+Wu(ricky_cx_wu)
+
+Created: Aug 19, 2024
+
+## Problem Description
+
+Currently, OpenBMC lacks a unified method that meets the needs of various
+vendors to record different types of BMC reboot cause event logs. The purpose of
+this proposal is to update the existing method, consolidating more BMC reboot
+causes to better align with current usage needs.
+
+## Background and References
+
+In the current approach, the only defined reboot causes are **WDIOF_EXTERN1**
+and **WDIOF_CARDRESET**, but this is insufficient to meet today's needs.
+However, due to varying needs among different vendors, it’s not feasible to
+cover all possible reboot causes. In this update, we will add support for
+several more common types.
+
+## Requirements
+
+1. Each BMC vendor needs to provide or update their driver to retrieve the
+   corresponding BMC reboot cause.
+2. Each BMC vendor needs to record the results of the retrieved reboot cause to
+   the specified path.
+3. Each vendor needs to ensure the accuracy of interpreting the reboot cause
+   results.
+4. New reboot cause types need to be defined to cover the requirements
+5. Revise the definitions of certain existing reboot cause types to better
+   represent their respective conditions.
+6. Ensure that methods based on the original design can adapt well to this
+   change.
+
+## Proposed Design
+
+```mermaid
+flowchart TD
+    A[BMC reboot] --> B[Driver get the reboot cause]
+    B --> C[Driver set the corresponding flag based on the reboot cause to /sys/class/watchdog/watchdog0/bootstatus]
+    C --> D[phosphor-state-manager get the flag]
+    D --> E[Log the corresponding event based the the different flag]
+```
+
+After a BMC reboot, each BMC vendor’s driver first retrieves the reboot cause.
+Then, based on the reboot cause, it sets different flags to the specified path.
+The PSM (Phosphor-state-manager) reads the flags from the specified path to
+determine the type of reboot cause. Finally, it generates the corresponding
+event log based on the determination.
+
+This process ensures accurate logging and handling of different BMC reboot
+causes, improving system reliability and monitoring. Belows are the details of
+the new additions and changes:
+
+1. Driver Provision by BMC Vendors:
+
+- Each BMC vendor must provide a driver to retrieve the BMC reboot cause and
+  record the result at the specified location.
+
+2. Redefining Reboot Cause Type **WDIOF_EXTERN1**:
+
+- This type will henceforth represent a software reset.
+
+3. Revise the Definition of **WDIOF_CARDRESET**:
+
+- The **WDIOF_CARDRESET** type will now specifically indicate resets caused by
+  the watchdog.
+
+4. Clarification of The **Power-on-reset case**:
+
+- When a BMC reset occured, but the flag in the bootstatus remains unchanged by
+  the watchdog driver (i.e., it stays at 0), this indicates that a
+  **Power-on-reset** has occurred.
+
+5. Update Reboot Cause Interpretation:
+
+| phosphor-state-manager | bootstatus value | watchdog driver                  |
+| ---------------------- | ---------------- | -------------------------------- |
+| WDIOF_EXTERN1          | 0x04             | return 0x04 if reset by Software |
+| WDIOF_CARDRESET        | 0x20             | return 0x20 if reset by Watchdog |
+| POR                    | 0x00             | Do nothing                       |
+
+6. Generate Corresponding Event Log:
+
+- After interpreting the reboot cause, the system should issue the corresponding
+  event log based on the determined type.
+
+## Alternatives Considered
+
+In the original approach, **WDIOF_CARDRESET** was used to represent a **POR**
+(power-on-reset). However, with the new method, we need to distinguish between
+watchdog resets and power-on resets. Therefore, we now use **WDIOF_CARDRESET**
+to represent watchdog resets, aligning with the existing kernel documentation
+and driver implementation.
+
+## Impacts
+
+1. Common reboot causes across vendors can be consolidated to issue a unified
+   event log.
+2. If any functions rely on the original reboot cause, the code must be adjusted
+   to align with the new definitions.
+
+### Organizational
+
+Which repositories are expected to be modified to execute this design?
+phosphor-state-manager
+
+## Testing
+
+Reboot the BMC under various conditions and check whether the corresponding
+event logs are generated correctly.