feat: Add /dev/mvsw_fw_comm_debug device for FW debugging

docs/dev.md

@@ -14,3 +14,103 @@ Finish this doc
 * Run `make rebuild` in $(ONL)/packages/base/$ARCH/foo to rebuild the package cache
     * particularly if you see an error like:
       """ERROR:onlpm:'Package all does not exist.'"""
+
+/dev/mvsw_fw_comm_debug - Character device for firmware debugging
+=================================================================
+
+Description
+-----------
+The `/dev/mvsw_fw_comm_debug` character device allows sending commands from user
+mode to the firmware running on the secondary CPU. This device is intended for
+debugging purposes and provides a limited set of commands to retrieve information
+about the firmware's status and execution environment.
+
+Usage
+-----
+The device accepts commands through the `write` system call, and the output is
+retrieved using the `read` system call. The "help" command lists all available
+commands and their descriptions.
+
+Command examples
+----------------
+
+### help
+The "help" command lists all available commands and their descriptions.
+
+```
+# echo "help" > mvsw_fw_comm_debug
+# cat mvsw_fw_comm_debug
+Available commands:
+ help - shows this prompt
+ system_metrics - shows system metrics from FW CPU
+ kernel_logs  - shows logs from kernel ring buffer
+ cpss_logs - shows logs of appDemo service
+ kernel_logs/cpss_logs <reset> - resets the pointer to the beginning of the logs
+ exec_luacli <command> - executes <command> in luaCLI in FW CPU
+```
+
+### system_metrics
+Retrieves system metrics from the firmware CPU, including memory, CPU, and filesystem usage.
+
+```
+root@netprod-dentlab-sea55-mendel-infra-sw1:/dev# echo "system_metrics" > mvsw_fw_comm_debug
+root@netprod-dentlab-sea55-mendel-infra-sw1:/dev# cat mvsw_fw_comm_debug
+              total        used        free      shared  buff/cache   available
+Mem:            997          49         825         112         123         816
+Swap:             0           0           0
+Filesystem                Size      Used Available Use% Mounted on
+devtmpfs                496.7M         0    496.7M   0% /dev
+tmpfs                   498.7M      4.0K    498.7M   0% /dev/shm
+tmpfs                   498.7M    112.8M    385.9M  23% /tmp
+tmpfs                   498.7M     20.0K    498.7M   0% /run
+Mem: 176684K used, 844648K free, 115524K shrd, 0K buff, 123076K cached
+CPU:  10% usr  10% sys   0% nic  80% idle   0% io   0% irq   0% sirq
+Load average: 0.23 0.34 0.36 1/67 1284
+  PID  PPID USER     STAT   VSZ %VSZ %CPU COMMAND
+ 1239     1 root     S     2928   0%   0% /sbin/getty -L console 0 vt100
+    1     0 root     S     2924   0%   0% init
+ 1196     1 root     S     2924   0%   0% /sbin/klogd -n
+ 1192     1 root     S     2924   0%   0% /sbin/syslogd -n
+```
+
+
+### exec_luacli
+Executes a command in the luaCLI environment running on the firmware CPU.
+
+```
+# echo "exec_luacli ?" > mvsw_fw_comm_debug
+# cat mvsw_fw_comm_debug
+Entering LuaCLI took 0.004775 msec
+
+ LUA CLI based on LUA 5.1 from www.lua.org
+ LUA CLI uses Mini-XML engine from www.minixml.org
+***************************************************
+               LUA CLI shell ready
+***************************************************
+
+Console# ?
+  autoInitSystem             Auto Init system (determines init params according to PCI/PEX scanning)
+  clear                      Reset functions
+  cls                        clear screen
+  configure                  Enter configuration mode
+  cpss-api
+  cpssInitSystem             Init system
+  cpssLsSmi                  Lists the SMI devices
+  cpssLspci                  Lists the PCI devices
+  cpssPciProvision           Insert Pci data of needed device, device number and hw device number
+  cpssPciRemove              Remove Pex device from sysfs
+  cpssPciRescan              rescan Pex devices
+  cpssPpInsert               Insert Packet Processor
+  cpssPpRemove               Remove Packet Processor
+  cpssPpShowDevices          Lists the Pp devices and PCI info
+  cpssSystemBaseInit         Init CPSS Base system- device independent
+  cpssinitsystem             Init system
+  dbg                        Allows to execute debug command while in other contexts
+  debug-mode                 Exit from the EXEC to debug mo
+  ...
+```
+
+
+Security Considerations
+-----------------------
+For security reasons, the list of commands available through `/dev/mvsw_fw_comm_debug` is limited to a predefined subset. This restriction is enforced to prevent execution of potentially harmful commands on the firmware CPU.