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

[Guenter Roeck]

On 01/23/2015 08:20 AM, Doug Anderson wrote:
> Guenter,
>
> On Fri, Jan 23, 2015 at 8:03 AM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On 01/22/2015 09:09 AM, Doug Anderson wrote:
> > > Jisheng,
> > >
> > > On Wed, Jan 21, 2015 at 9:22 PM, Jisheng Zhang <jszhang@xxxxxxxxxxx>
> > > wrote:
> > > > Dear Doug,
> > > >
> > > > On Wed, 21 Jan 2015 15:17:22 -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.
> > > >
> > > >
> > > > + 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".
> > Not sure where that leaves us. Does that mean the driver supports different
> > hardware with different register sets ?
>
> Apparently so.  I've only seen the documentation from rk3288, but it's
> clearly different than what you saw.
>
> >   Should that be documented in the
> > driver,
>
> Probably not a terrible idea.
>
> > and should we have (or do we need) different compatible statements for those
> > variants, and conditional code in the driver ?
>
> I'm not sure we actually need any conditional code.  I've put the
> other patch on rk3288 and it didn't hurt to write those reserved bits.
> I also can't quite believe that the extra pat will hurt on other
> hardware.
>
>
> > And does it mean we need both patches, at least for some of the hardware
> > variants ? If so, what happens if those patches are applied and the
> > resulting
> > driver runs on the other hardware ?
>
> I think it should be fine.
>
>
> Do you want me to spin my patch and add some extra comments (but
> otherwise keep it roughly unchanged?).  We can get Jisheng to add his
> Tested-by...

Yes, that would be great.

Thanks,
Guenter

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