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

From: Rasmus Villemoes
Date: Wed Jul 20 2016 - 17:38:05 EST

On 2016-07-15 15:46, Guenter Roeck wrote:
On 07/15/2016 01:15 AM, Rasmus Villemoes wrote:

+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

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
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.

Well, if the bit isn't cleared here, but it was set during probe(), the framework will (re)start this watchdog (and keep it fed) since there's no separate ping method. I suppose that's reasonable semantics if the watchdog was running at boot (and I like how that ends up interacting with my open_deadline proposal), but probably a little too subtle. This would also change if the ->start method was broken up into separate ping and start methods, which it seems that it could be.

If we do clear the bit here, I think it's neater to set it in start as well, even if that doesn't really have any effect.