linux-kernel - Re: [PATCH v2 1/2] watchdog: dw_wdt: pat the watchdog before enabling it

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Message-ID: <20150127114909.204eeee0@xhacker>
Date:	Tue, 27 Jan 2015 11:49:09 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Doug Anderson <dianders@...omium.org>
CC:	Wim Van Sebroeck <wim@...ana.be>,
	Guenter Roeck <linux@...ck-us.net>,
	Heiko Stuebner <heiko@...ech.de>,
	Lunxue Dai <lunxue.dai@...k-chips.com>,
	Dinh Nguyen <dinguyen@...era.com>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] watchdog: dw_wdt: pat the watchdog before
 enabling it

Dear Doug,

On Mon, 26 Jan 2015 15:27:15 -0800
Doug Anderson <dianders@...omium.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_mmc versions by using the

s/dw_mmc/dw_wdt

> 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.

Based on your register dumping, I see the following configurations on rk3288:

WDT_DUAL_TOP is configured as false, so there's no TOP_INIT

WDT_DFLT_TOP is configured as 0, so it will timeout soon.


So an extra pat is a must on such platforms with similar configurations. And it
doesn't hurt anything if we have an extra pat before enabling the WDT

All in all, except the "dw_mmc" typo above, the patch looks good to me.

Thanks,
Jisheng

> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
> 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 | 19 +++++++++++++------
>  1 file changed, 13 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
> index b34a2e4..2c24882 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;
> @@ -114,17 +120,18 @@ static int dw_wdt_set_top(unsigned top_s)
>  	writel(top_val | top_val << WDOG_TIMEOUT_RANGE_TOPINIT_SHIFT,
>  		dw_wdt.regs + WDOG_TIMEOUT_RANGE_REG_OFFSET);
>  
> +	/*
> +	 * On some versions of dw_wdt writing to TOPINIT counts as a pat
> +	 * (kick) of the watchdog; for other version of dw_wdt bits 4-7
> +	 * are reserved and we need to pat the watchdog dog manually.
> +	 */
> +	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)
>  {

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