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

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Message-ID: <20140923145756.0940559e@xhacker>
Date:	Tue, 23 Sep 2014 14:57:56 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Guenter Roeck <linux@...ck-us.net>
CC:	"wim@...ana.be" <wim@...ana.be>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 2/2] watchdog: dw_wdt: add restart handler support

Dear Guenter,

On Sat, 20 Sep 2014 07:08:22 -0700
Guenter Roeck <linux@...ck-us.net> wrote:

> 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);

> Another comment: You should probably wait here for a bit to let the reset
> catch.

will do in next version. Thanks for pointing out

> >
> > 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.
> 

we want to handle the reboot case if wdt is in already use. In this case,
we dunno what's the timeout period, but obviously it's not as short as 2^16/clk
So we change the timeout period by writing 0 into WDOG_TIMEOUT_RANGE_REG_OFFSET
to select the minimum timeout period. But per the datasheet, a change of the
timeout period takes effect only after the next counter restart. So we programming
the restart register to kick off next counter restart.

Thanks for reviewing,
Jisheng

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