[PATCH] watchdog: gpio_wdt: add support for stoppable devices

[Rasmus Villemoes]

Back when I added this driver in commit 2ac8490412c9, I wrote

    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;

That has changed now; I have a board with just such a watchdog on my
desk currently. Add support for that.

- For a hw_algo="toggle" device, the gpio is requested as output if the
  always-running flag is set, otherwise as input.

- The ->start() method is updated to change the direction to output when
  required (i.e. it is not always-running).

- The ->stop() method is implemented, but of course reports failure if
  always-running.

As I still haven't met any hw_algo="level" devices, I'm not entirely
sure how they fit in, but I'm borrowing logic from the corresponding
linux driver:

- In ->probe(), such devices always request the gpio as GPIOD_IS_OUT.

- In ->stop(), the linux driver has an "eternal ping" comment and sets
  the gpio to (logic) high.

Signed-off-by: Rasmus Villemoes <r...@prevas.dk>
---
 drivers/watchdog/gpio_wdt.c | 27 ++++++++++++++++++++++++---
 1 file changed, 24 insertions(+), 3 deletions(-)

diff --git a/drivers/watchdog/gpio_wdt.c b/drivers/watchdog/gpio_wdt.c
index 2920c2c751f..e889861e917 100644
--- a/drivers/watchdog/gpio_wdt.c
+++ b/drivers/watchdog/gpio_wdt.c
@@ -45,14 +45,32 @@ static int gpio_wdt_start(struct udevice *dev, u64 timeout, 
ulong flags)
        if (priv->always_running)
                return 0;
 
-       return -ENOSYS;
+       dm_gpio_set_dir_flags(&priv->gpio, GPIOD_IS_OUT);
+       gpio_wdt_reset(dev);
+
+       return 0;
+}
+
+static int gpio_wdt_stop(struct udevice *dev)
+{
+       struct gpio_wdt_priv *priv = dev_get_priv(dev);
+
+       if (priv->always_running)
+               return -EOPNOTSUPP;
+
+       if (priv->hw_algo == HW_ALGO_TOGGLE)
+               dm_gpio_set_dir_flags(&priv->gpio, GPIOD_IS_IN);
+       else
+               dm_gpio_set_value(&priv->gpio, 1);
+
+       return 0;
 }
 
 static int dm_probe(struct udevice *dev)
 {
        struct gpio_wdt_priv *priv = dev_get_priv(dev);
-       int ret;
        const char *algo = dev_read_string(dev, "hw_algo");
+       int ret, flags;
 
        if (!algo)
                return -EINVAL;
@@ -64,7 +82,9 @@ static int dm_probe(struct udevice *dev)
                return -EINVAL;
 
        priv->always_running = dev_read_bool(dev, "always-running");
-       ret = gpio_request_by_name(dev, "gpios", 0, &priv->gpio, GPIOD_IS_OUT);
+       flags = priv->always_running || priv->hw_algo == HW_ALGO_LEVEL ?
+               GPIOD_IS_OUT : GPIOD_IS_IN;
+       ret = gpio_request_by_name(dev, "gpios", 0, &priv->gpio, flags);
        if (ret < 0) {
                dev_err(dev, "Request for wdt gpio failed: %d\n", ret);
                return ret;
@@ -78,6 +98,7 @@ static int dm_probe(struct udevice *dev)
 
 static const struct wdt_ops gpio_wdt_ops = {
        .start = gpio_wdt_start,
+       .stop  = gpio_wdt_stop,
        .reset = gpio_wdt_reset,
 };
 
-- 
2.46.2