Dear Doug,
On Wed, 21 Jan 2015 15:17:22 -0800
Doug Anderson <dianders@xxxxxxxxxxxx> wrote:
> On some dw_wdt implementations the "top" register may be initted to 0
> at bootup. In such a case, each "pat" of the watchdog will reset the
> timer to 0xffff. That's pretty short.
+ Guenter Roeck
This should have been fixed by dfa07141e7a792("watchdog: dw_wdt: initialise
TOP_INIT in dw_wdt_set_top()")
In fact, my original fix is as similar as your patch
http://www.spinics.net/lists/arm-kernel/msg363658.html
Then Guenter Roeck suggest one elegant solution which is the base of
commit dfa07141e7a792.
http://www.spinics.net/lists/arm-kernel/msg363908.html
>
> The input clock of the wdt can be any of a wide range of values. On
> an rk3288 system, I've seen the wdt clock be 24.75 MHz. That means
> each tick is ~40ns and we'll count to 0xffff in ~2.6ms.
>
> Because of the above two facts, it's a really good idea to pat the
> watchdog after initting the "top" register properly and before
> enabling the watchdog. If you don't then there's no way we'll get the
> next heartbeat in time.
>
> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> ---
> drivers/watchdog/dw_wdt.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> index b34a2e4..fc92bea 100644
> --- a/drivers/watchdog/dw_wdt.c
> +++ b/drivers/watchdog/dw_wdt.c
> @@ -170,6 +170,7 @@ static int dw_wdt_open(struct inode *inode, struct file
> *filp)
> * the maximum and then start it.
> */
> dw_wdt_set_top(DW_WDT_MAX_TOP);
> + dw_wdt_keepalive();
> writel(WDOG_CONTROL_REG_WDT_EN_MASK,
> dw_wdt.regs + WDOG_CONTROL_REG_OFFSET);
> }
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