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

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Date:	Fri, 23 Jan 2015 09:02:51 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Doug Anderson <dianders@...omium.org>
CC:	Jisheng Zhang <jszhang@...vell.com>,
	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

On 01/23/2015 08:20 AM, Doug Anderson wrote:
> Guenter,
>
> On Fri, Jan 23, 2015 at 8:03 AM, Guenter Roeck <linux@...ck-us.net> wrote:
>> On 01/22/2015 09:09 AM, Doug Anderson 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".
>>>
>> 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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