linux-kernel - Re: [PATCH 2/2] watchdog: dw_wdt: add restart handler support

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Date:	Sat, 20 Sep 2014 07:08:22 -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 2/2] watchdog: dw_wdt: add restart handler support

On 09/19/2014 08:07 PM, Guenter Roeck wrote:
> On 09/18/2014 11:29 PM, Jisheng Zhang wrote:
>> The kernel core now provides an API to trigger a system restart.
>> Register with it to support restarting the system via. watchdog.
>>
>> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
>> ---
>>   drivers/watchdog/dw_wdt.c | 27 +++++++++++++++++++++++++++
>>   1 file changed, 27 insertions(+)
>>
>> diff --git a/drivers/watchdog/dw_wdt.c b/drivers/watchdog/dw_wdt.c
>> index ad0619d..4ca41e9 100644
>> --- a/drivers/watchdog/dw_wdt.c
>> +++ b/drivers/watchdog/dw_wdt.c
>> @@ -29,9 +29,11 @@
>>   #include <linux/miscdevice.h>
>>   #include <linux/module.h>
>>   #include <linux/moduleparam.h>
>> +#include <linux/notifier.h>
>>   #include <linux/of.h>
>>   #include <linux/pm.h>
>>   #include <linux/platform_device.h>
>> +#include <linux/reboot.h>
>>   #include <linux/spinlock.h>
>>   #include <linux/timer.h>
>>   #include <linux/uaccess.h>
>> @@ -62,6 +64,7 @@ static struct {
>>       unsigned long        next_heartbeat;
>>       struct timer_list    timer;
>>       int            expect_close;
>> +    struct notifier_block    restart_handler;
>>   } dw_wdt;
>>
>>   static inline int dw_wdt_is_enabled(void)
>> @@ -119,6 +122,22 @@ static void dw_wdt_keepalive(void)
>>              WDOG_COUNTER_RESTART_REG_OFFSET);
>>   }
>>
>> +static int dw_wdt_restart_handle(struct notifier_block *this,
>> +                unsigned long mode, void *cmd)
>> +{
>> +    u32 val;
>> +
>> +    writel(0, dw_wdt.regs + WDOG_TIMEOUT_RANGE_REG_OFFSET);
>> +    val = readl(dw_wdt.regs + WDOG_CONTROL_REG_OFFSET);
>> +    if (val & WDOG_CONTROL_REG_WDT_EN_MASK)
>> +        writel(WDOG_COUNTER_RESTART_KICK_VALUE, dw_wdt.regs +
>> +            WDOG_COUNTER_RESTART_REG_OFFSET);
>> +    else
>> +        writel(WDOG_CONTROL_REG_WDT_EN_MASK,
>> +               dw_wdt.regs + WDOG_CONTROL_REG_OFFSET);
>
> Don't you have to write WDOG_COUNTER_RESTART_KICK_VALUE into
> WDOG_COUNTER_RESTART_REG_OFFSET in the else case as well ?
>

According to the datasheet, it should be sufficient to
- Write 0 into WDOG_TIMEOUT_RANGE_REG_OFFSET to select the minimum timeout period
- Write 0x1 into WDOG_CONTROL_REG_OFFSET to enable the watchdog and select reset
   as desired action. This can be unconditional.

Writing into the restart register should not be necessary.

Thanks,
Guenter

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