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SubjectRe: [PATCH] watchdog: gpio_wdt: Support GPO lines with the toggle algorithm
On 3/22/22 15:29, Tobias Waldekranz wrote:
> Support using GPO lines (i.e. GPIOs that are output-only) with
> gpio_wdt using the "toggle" algorithm.
>
> Since its inception, gpio_wdt has configured its GPIO line as an input
> when using the "toggle" algorithm, even though it is used as an output
> when kicking. This needlessly barred hardware with output-only pins
> from using the driver.
>
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
> ---
>
> Hi,
>
> This patch has been in our downstream tree for a long time. We need it
> because our kick GPIO can't be used as an input.
>
> What I really can't figure out is why the driver would request the pin
> as in input, when it's always going to end up being used as an output
> anyway.
>
> So I thought I'd send it upstream in the hopes of either getting it
> merged, or an explanation as to why it is needed.
>

I _think_ the assumption / idea was that "toggle" implies that the output
is connected to a pull-up resistor and that the pin either floats or is
pulled down to ground, causing the signal to toggle. I don't know if/how
that works in practice, though.

Guenter

> drivers/watchdog/gpio_wdt.c | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/watchdog/gpio_wdt.c b/drivers/watchdog/gpio_wdt.c
> index 0923201ce874..f7686688e0e2 100644
> --- a/drivers/watchdog/gpio_wdt.c
> +++ b/drivers/watchdog/gpio_wdt.c
> @@ -108,7 +108,6 @@ static int gpio_wdt_probe(struct platform_device *pdev)
> struct device *dev = &pdev->dev;
> struct device_node *np = dev->of_node;
> struct gpio_wdt_priv *priv;
> - enum gpiod_flags gflags;
> unsigned int hw_margin;
> const char *algo;
> int ret;
> @@ -122,17 +121,15 @@ static int gpio_wdt_probe(struct platform_device *pdev)
> ret = of_property_read_string(np, "hw_algo", &algo);
> if (ret)
> return ret;
> - if (!strcmp(algo, "toggle")) {
> +
> + if (!strcmp(algo, "toggle"))
> priv->hw_algo = HW_ALGO_TOGGLE;
> - gflags = GPIOD_IN;
> - } else if (!strcmp(algo, "level")) {
> + else if (!strcmp(algo, "level"))
> priv->hw_algo = HW_ALGO_LEVEL;
> - gflags = GPIOD_OUT_LOW;
> - } else {
> + else
> return -EINVAL;
> - }
>
> - priv->gpiod = devm_gpiod_get(dev, NULL, gflags);
> + priv->gpiod = devm_gpiod_get(dev, NULL, GPIOD_OUT_LOW);
> if (IS_ERR(priv->gpiod))
> return PTR_ERR(priv->gpiod);
>

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