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u-boot/doc/device-tree-bindings/watchdog/gpio-wdt.txt

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watchdog: add gpio watchdog driver 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_giA@mail.gmail.com/ 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. Reviewed-by: Simon Glass <sjg@chromium.org> Reviewed-by: Stefan Roese <sr@denx.de> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
2021-08-19 09:57:04 +00:00
GPIO watchdog timer
Describes a simple watchdog timer which is reset by toggling a gpio.
Required properties:
- compatible: Must be "linux,wdt-gpio".
watchdog: add pulse support to gpio watchdog driver A common external watchdog circuit is kept alive by triggering a short pulse on the reset pin. This patch adds support for this use case, while making the algorithm configurable in the devicetree. The "linux,wdt-gpio" driver being modified is based off the equivalent driver in the Linux kernel, which provides support for this algorithm. This patch brings parity to this driver, and is kept aligned with the functionality and devicetree configuration in the kernel. It should be noted that this adds a required property named 'hw_algo' to the devicetree binding, following suit with the kernel. I'm happy to make this backward-compatible if preferred. Signed-off-by: Paul Doelle <paaull.git@gmail.com> Reviewed-by: Stefan Roese <sr@denx.de>
2022-07-04 09:00:25 +00:00
- gpios: From common gpio binding; gpio connection to WDT reset pin.
- hw_algo: The algorithm used by the driver. Should be one of the
following values:
- toggle: Toggle from high-to-low or low-to-high when resetting the watchdog.
- level: Maintain a constant high/low level, and trigger a short pulse when
resetting the watchdog. Active level is determined by the GPIO flags.
watchdog: add gpio watchdog driver 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_giA@mail.gmail.com/ 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. Reviewed-by: Simon Glass <sjg@chromium.org> Reviewed-by: Stefan Roese <sr@denx.de> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
2021-08-19 09:57:04 +00:00
- always-running: Boolean property indicating that the watchdog cannot
be disabled. At present, U-Boot only supports this kind of GPIO
watchdog.
Example:
gpio-wdt {
gpios = <&gpio0 1 0>;
compatible = "linux,wdt-gpio";
watchdog: add pulse support to gpio watchdog driver A common external watchdog circuit is kept alive by triggering a short pulse on the reset pin. This patch adds support for this use case, while making the algorithm configurable in the devicetree. The "linux,wdt-gpio" driver being modified is based off the equivalent driver in the Linux kernel, which provides support for this algorithm. This patch brings parity to this driver, and is kept aligned with the functionality and devicetree configuration in the kernel. It should be noted that this adds a required property named 'hw_algo' to the devicetree binding, following suit with the kernel. I'm happy to make this backward-compatible if preferred. Signed-off-by: Paul Doelle <paaull.git@gmail.com> Reviewed-by: Stefan Roese <sr@denx.de>
2022-07-04 09:00:25 +00:00
hw_algo = "toggle";
watchdog: add gpio watchdog driver 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_giA@mail.gmail.com/ 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. Reviewed-by: Simon Glass <sjg@chromium.org> Reviewed-by: Stefan Roese <sr@denx.de> Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
2021-08-19 09:57:04 +00:00
always-running;
};
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