On Thu, 27 May 2021 at 16:00, Rasmus Villemoes rasmus.villemoes@prevas.dk wrote:
A rather common kind of external watchdog circuit is one that is kept alive by toggling a gpio. Add a driver for handling such a watchdog.
The corresponding linux driver apparently has support for some watchdog circuits which can be disabled by tri-stating the gpio, but I have never actually encountered such a chip in the wild; the whole point of adding an external watchdog is usually that it is not in any way under software control. For forward-compatibility, and to make DT describe the hardware, the current driver only supports devices that have the always-running property. I went a little back and forth on whether I should fail ->probe or only ->start, and ended up deciding ->start was the right place.
The compatible string is probably a little odd as it has nothing to do with linux per se - however, I chose that to make .dts snippets reusable between device trees used with U-Boot and linux, and this is the (only) compatible string that linux' corresponding driver and DT binding accepts. I have asked whether one should/could add "wdt-gpio" to that binding, but the answer was no:
https://lore.kernel.org/lkml/CAL_JsqKEGaFpiFV_oAtE+S_bnHkg4qry+bhx2EDs=NSbVf...
If someone feels strongly about this, I can certainly remove the "linux," part from the string - it probably wouldn't the only place where one can't reuse a DT snippet as-is between linux and U-Boot.
Signed-off-by: Rasmus Villemoes rasmus.villemoes@prevas.dk
.../watchdog/gpio-wdt.txt | 19 +++++ drivers/watchdog/Kconfig | 9 +++ drivers/watchdog/Makefile | 1 + drivers/watchdog/gpio_wdt.c | 69 +++++++++++++++++++ 4 files changed, 98 insertions(+) create mode 100644 doc/device-tree-bindings/watchdog/gpio-wdt.txt create mode 100644 drivers/watchdog/gpio_wdt.c
Reviewed-by: Simon Glass sjg@chromium.org