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

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Date:	Mon, 26 Jan 2015 14:22:10 +0800
From:	Jisheng Zhang <jszhang@...vell.com>
To:	Doug Anderson <dianders@...omium.org>
CC:	Guenter Roeck <linux@...ck-us.net>,
	Wim Van Sebroeck <wim@...ana.be>,
	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 1/2] watchdog: dw_wdt: pat the watchdog before enabling
 it

Dear Doug,

On Thu, 22 Jan 2015 09:09:28 -0800
Doug Anderson <dianders@...omium.org> wrote:

> Jisheng,
> 
> On Wed, Jan 21, 2015 at 9:22 PM, Jisheng Zhang <jszhang@...vell.com> wrote:
> > Dear Doug,
> >
> > On Wed, 21 Jan 2015 15:17:22 -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.
> >
> > + Guenter Roeck
> >
> > This should have been fixed by dfa07141e7a792("watchdog: dw_wdt:
> > initialise TOP_INIT in dw_wdt_set_top()")
> 
> I will admit that I'm testing on a tree that doesn't have your patch
> (I'm on a 3.14 kernel with lots of backports).  ...but I did try
> cherry-picking your patch before I wrote up mine and it didn't fix my
> problem.  I believe that the watchdog that's in Rockchip rk3288 must
> be a slightly different version of the IP block than you're working
> with.
> 
> Specifically I see the register WDT_TORR that has an offset of 0x4.
> That's the RANGE_REG in your code.  It shows bits 3:0 set the timeout
> period (0 = 0xffff and 15 = 0x7fffffff).  It shows bits 31:4 as
> "reserved".

Could you please dump registers' value at offset 0xf4 and 0xf8 if you don't mind?

Thanks,
Jisheng

> 
> 
> > In fact, my original fix is as similar as your patch
> >
> > http://www.spinics.net/lists/arm-kernel/msg363658.html
> 
> Yup, except that I pat the watchdog before enabling it and you pat it
> after...  It probably doesn't matter as long as the two instructions
> are within 2.5ms of each other, but it seems nice to be safer.
> 
> -Doug

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