linux-kernel - Re: [PATCH 1/2] watchdog: dw_wdt: restart the counter immediately after enabling WDT

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Date:	Sat, 20 Sep 2014 06:51:56 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Jisheng Zhang <jszhang@...vell.com>, wim@...ana.be
CC:	linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] watchdog: dw_wdt: restart the counter immediately
 after enabling WDT

On 09/18/2014 11:29 PM, Jisheng Zhang wrote:
> The TOP_INIT may be zero, so the timeout period may be very short after
> initialization is done, thus the system may be reset soon after enabling.
> We fix this problem by restarting the counter immediately after enabling
> WDT.
>
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> ---
>   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 9f21029..ad0619d 100644
> --- a/drivers/watchdog/dw_wdt.c
> +++ b/drivers/watchdog/dw_wdt.c
> @@ -146,6 +146,7 @@ static int dw_wdt_open(struct inode *inode, struct file *filp)
>   		dw_wdt_set_top(DW_WDT_MAX_TOP);
>   		writel(WDOG_CONTROL_REG_WDT_EN_MASK,
>   		       dw_wdt.regs + WDOG_CONTROL_REG_OFFSET);
> +		dw_wdt_keepalive();
>   	}
>
>   	dw_wdt_set_next_heartbeat();
>
After getting access to the datasheet, I concluded that this fix is wrong
or at least more risky than necessary. The datasheet states that top_init,
ie bit 4-7 of the wdt_torr register, needs to be initialized with the desired
timeout period prior to enabling the watchdog. dw_wdt_set_top() sets it to
0 instead, ie to the lowest possible timeout period.

Guenter

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