On Tue, 27 Jan 2015 14:25:16 -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.
>
> 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.
>
> Jisheng Zhang fixed this problem on some dw_wdt versions by using the
> TOP_INIT feature. However, the dw_wdt on rk3288 doesn't have TOP_INIT
> so it's a good idea to also pat the watchdog manually.
>
> Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx>
> ---
> Changes in v3:
> - Better comments now that we know what's going on.
> - Don't typo dw_wdt as dw_mmc.
>
> Changes in v2:
> - Add comment about why TOP_INIT doesn't work on rk3288; move pat
> to right next to the attempt to use TOP_INIT.
>
> drivers/watchdog/dw_wdt.c | 26 +++++++++++++++++++-------
> 1 file changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> index b34a2e4..3dde6de 100644
> --- a/drivers/watchdog/dw_wdt.c
> +++ b/drivers/watchdog/dw_wdt.c
> @@ -96,6 +96,12 @@ static inline void dw_wdt_set_next_heartbeat(void)
> dw_wdt.next_heartbeat = jiffies + dw_wdt_get_top() * HZ;
> }
>
> +static void dw_wdt_keepalive(void)
> +{
> + writel(WDOG_COUNTER_RESTART_KICK_VALUE, dw_wdt.regs +
> + WDOG_COUNTER_RESTART_REG_OFFSET);
> +}
> +
> static int dw_wdt_set_top(unsigned top_s)
> {
> int i, top_val = DW_WDT_MAX_TOP;
> @@ -110,21 +116,27 @@ static int dw_wdt_set_top(unsigned top_s)
> break;
> }
>
> - /* Set the new value in the watchdog. */
> + /*
> + * Set the new value in the watchdog. Some versions of dw_wdt
> + * have have TOPINIT in the TIMEOUT_RANGE register (as per
> + * CP_WDT_DUAL_TOP in WDT_COMP_PARAMS_1). On those we
> + * effectively get a pat of the watchdog right here.
> + */
> writel(top_val | top_val << WDOG_TIMEOUT_RANGE_TOPINIT_SHIFT,
> dw_wdt.regs + WDOG_TIMEOUT_RANGE_REG_OFFSET);
>
> + /*
> + * Add an explicit pat to handle versions of the watchdog that
> + * don't have TOPINIT. This won't hurt on versions that have
> + * it.
> + */
> + dw_wdt_keepalive();
> +
> dw_wdt_set_next_heartbeat();
>
> return dw_wdt_top_in_seconds(top_val);
> }
>
> -static void dw_wdt_keepalive(void)
> -{
> - writel(WDOG_COUNTER_RESTART_KICK_VALUE, dw_wdt.regs +
> - WDOG_COUNTER_RESTART_REG_OFFSET);
> -}
> -
> static int dw_wdt_restart_handle(struct notifier_block *this,
> unsigned long mode, void *cmd)
> {
Looks good to me
Thanks
--
To unsubscribe from this list: send the line "unsubscribe linux-watchdog" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
