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

[Guenter Roeck]

On 01/26/2015 07:49 PM, Jisheng Zhang wrote:
> Dear Doug,
>
> On Mon, 26 Jan 2015 15:27:15 -0800
> Doug Anderson <dianders@xxxxxxxxxxxx> 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.

Jisheng,

it would be great if you can provide configuration information shown in
the (undocumented) registers.

Doug,

can you send another version with this information added as comment
to the code ? This will help others to understand what is going on
(and why) later on.

Thanks,
Guenter

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