Re: [PATCH 3/3] watchdog: bcm2835_wdt: set WDOG_HW_RUNNING bit when appropriate

[Guenter Roeck]

On 07/15/2016 01:15 AM, Rasmus Villemoes wrote:

A bootloader may start the watchdog device before handing control to
the kernel - in that case, we should tell the kernel about it so the
watchdog framework can keep it alive until userspace opens
/dev/watchdog0.

Separate note: The maximum timeout for this watchdog is 15 seconds.
Given that, it might be useful to set max_hw_heartbeat_ms instead of
max_timeout. Separate patch, though.

Signed-off-by: Rasmus Villemoes <rasmus.villem...@prevas.dk>
---
  drivers/watchdog/bcm2835_wdt.c | 22 ++++++++++++++++++++++
  1 file changed, 22 insertions(+)

diff --git a/drivers/watchdog/bcm2835_wdt.c b/drivers/watchdog/bcm2835_wdt.c
index 4dddd82..9a08334 100644
--- a/drivers/watchdog/bcm2835_wdt.c
+++ b/drivers/watchdog/bcm2835_wdt.c
@@ -55,6 +55,15 @@ struct bcm2835_wdt {
  static unsigned int heartbeat;
  static bool nowayout = WATCHDOG_NOWAYOUT;

+static bool bcm2835_wdt_is_running(struct bcm2835_wdt *wdt)
+{
+       uint32_t cur;
+
+       cur = readl(wdt->base + PM_RSTC);
+
+       return !!(cur & PM_RSTC_WRCFG_FULL_RESET);
+}
+
  static int bcm2835_wdt_start(struct watchdog_device *wdog)
  {
        struct bcm2835_wdt *wdt = watchdog_get_drvdata(wdog);
@@ -70,6 +79,7 @@ static int bcm2835_wdt_start(struct watchdog_device *wdog)
                  PM_RSTC_WRCFG_FULL_RESET, wdt->base + PM_RSTC);

        spin_unlock_irqrestore(&wdt->lock, flags);
+       set_bit(WDOG_HW_RUNNING, &wdog->status);

You don't need to set this bit here unless the watchdog can not be stopped.

        return 0;
  }
@@ -79,6 +89,7 @@ static int bcm2835_wdt_stop(struct watchdog_device *wdog)
        struct bcm2835_wdt *wdt = watchdog_get_drvdata(wdog);

        writel_relaxed(PM_PASSWORD | PM_RSTC_RESET, wdt->base + PM_RSTC);
+       clear_bit(WDOG_HW_RUNNING, &wdog->status);

... and since you clear the bit, it can be stopped. Both setting and resetting 
the bit
is therefore not necessary.

        return 0;
  }

@@ -181,6 +192,17 @@ static int bcm2835_wdt_probe(struct platform_device *pdev)
        watchdog_init_timeout(&bcm2835_wdt_wdd, heartbeat, dev);
        watchdog_set_nowayout(&bcm2835_wdt_wdd, nowayout);
        bcm2835_wdt_wdd.parent = &pdev->dev;
+       if (bcm2835_wdt_is_running(wdt)) {
+               /*
+                * The currently active timeout value (set by the
+                * bootloader) may be different from the module
+                * heartbeat parameter or the value in device
+                * tree. But we just need to set WDOG_HW_RUNNING,
+                * because then the framework will "immediately" ping
+                * the device, updating the timeout.
+                */
+               set_bit(WDOG_HW_RUNNING, &bcm2835_wdt_wdd.status);
+       }
        err = watchdog_register_device(&bcm2835_wdt_wdd);
        if (err) {
                dev_err(dev, "Failed to register watchdog device");