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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>
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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>
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