Re: [PATCH v3 1/2] watchdog: dw_wdt: pat the watchdog before enabling it

[Jisheng Zhang <jszhang@marvell.com>]

On Tue, 27 Jan 2015 14:25:16 -0800
Doug Anderson <dianders@chromium.org> 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@chromium.org>
> ---
> 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