Introduction

This page describes the Window watchdog driver which is available in mainline and Xilinx Linux distribution as drivers/watchdog/xilinx_wwdt.c

HW IP Features

The window watchdog timer mode is enabled by the Enable_and_Status [WEN] bit. The two windowed watchdog timer modes are basic and Q&A, and the mode is selected by the Funct_Ctrl [WM] bit.

In both windowed modes, the timer starts with the first window defined by a 32-bit field in the First_Wind register. The first window is considered the closed window. This is followed by a second window defined by another 32-bit field in the Second_Wind register. The second window is considered the open window. The protocol to keep the watchdog timer operating correctly depends on the window mode and the optional features that are enabled. In the simplest mode, the timer is restarted during the open window time.

Normally, if software tries to restart the timer before the open window time period, a bad event occurs, and the timer can generate a system interrupt or reset.

The Q&A token window mode requires the system software to write three one-byte responses during the first window (closed window) and a one-byte write in the second window (open window). The value of the token responses are based on the seed, feedback, and an answer count value. The seed and feedback values are programmed by software. The answer count value increments by one for each token response.

The two window timer modes include:

Windowed Basic Mode
Windowed Q&A Mode

For more details refer Versal TRM.

Known Issues and Limitations

The current driver does not support Windowed Q&A mode.

Kernel Configuration

The following config options should be enabled in order to build the xilinx window watchdog driver:

CONFIG_XILINX_WINDOW_WATCHDOG

CONFIG_WATCHDOG

│ Symbol: XILINX_WINDOW_WATCHDOG [=y] │ 
│ Type : tristate │ 
│ Defined at drivers/watchdog/Kconfig:307 │ 
│ Prompt: Xilinx window watchdog timer │ 
│ Depends on: WATCHDOG [=y] && HAS_IOMEM [=y] && (ARM64 [=y] || COMPILE_TEST [=n]) │ 
│ Location: │ 
│ -> Device Drivers │ 
│ -> Watchdog Timer Support (WATCHDOG [=y]) │ 
│ (1) -> Xilinx window watchdog timer (XILINX_WINDOW_WATCHDOG [=y]) │ 
│ Selects: WATCHDOG_CORE [=y]

Devicetree

For more details, please refer
Documentation/devicetree/bindings/watchdog/xlnx,versal-wwdt.yaml
Example:

watchdog@fd4d0000 {
	compatible = "xlnx,versal-wwdt";
	reg = <0xfd4d0000 0x10000>;
	clocks = <&clock25>;
	timeout-sec = <30>;
};

Test procedure

Start the watchdog timer, if there is no ping till the timeout seconds, it will generate reset interrupt at timeout seconds

echo s > /dev/watchdog

vck190

[    9.322914] Xilinx window watchdog fd4d0000.watchdog: Xilinx window watchdog Timer with timeout 20s

xilinx-vck190-20241:/home/petalinux# echo s > /dev/watchdog 
[  100.667738] watchdog: watchdog0: nowayout prevents watchdog being stopped!
[  100.674655] watchdog: watchdog0: watchdog did not stop!


[172464.626]PMC EAM ERR1: 0x200
[172464.676]PSM EAM Interrupt: ERR1: 0x0 ERR2: 0x2 
[172469.164]Received EAM error. ErrorNodeId: 0x2810C000, Register Mask: 0x2. The corresponding Error ID: 0x61

Ping test using watchdog-test app

xilinx-vck190-20241:/home/petalinux#./watchdog-test

Ping every 1 sec.

vck190

[    9.322914] Xilinx window watchdog fd4d0000.watchdog: Xilinx window watchdog Timer with timeout 20s

xilinx-vck190-20241:/home/petalinux# ./watchdog-test 
Watchdog Ticking Away!
................................................................................

Mainline Status

This driver is currently in sync with the mainline kernel except for the following:
- watchdog: xilinx_wwdt: Add check for timeout limit and set maximum value if exceeded

Change Log

2024.1
- Summary
  - watchdog: xilinx_wwdt: Add check for timeout limit and set maximum value if exceeded
  - watchdog: xilinx_wwdt: Use div_u64() in xilinx_wwdt_start()
  - watchdog: Explicitly include correct DT includes
- Commits
  - 3860676 watchdog: xilinx_wwdt: Add check for timeout limit and set maximum value if exceeded
  - 98334dc watchdog: xilinx_wwdt: Use div_u64() in xilinx_wwdt_start()
  - cc85f87 watchdog: Explicitly include correct DT includes
2023.2
- Summary
  - watchdog: xilinx_wwdt: Add "xlnx,versal-wwdt-1.0" compatible
  - watchdog: xilinx_wwdt: Add Versal window watchdog support
- Commits
  - 6d768de watchdog: xilinx_wwdt: Add "xlnx,versal-wwdt-1.0" compatible
  - f1b7739 watchdog: xilinx_wwdt: Add Versal window watchdog support

Xilinx Wiki

Window Watchdog