linux-kernel - Re: [PATCH 2/2] ARM: rockchip: disable watchdog during suspend

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Message-ID: <CAD=FV=WqdVD9_LGtYCHV-T3hTbq8wZ8z52rdD5HF7eHLWf8kTQ@mail.gmail.com>
Date:	Wed, 11 Mar 2015 14:23:38 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Chris Zhong <zyw@...k-chips.com>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Sonny Rao <sonnyrao@...omium.org>,
	"open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
	Daniel Kurtz <djkurtz@...gle.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] ARM: rockchip: disable watchdog during suspend

Hi,

On Mon, Mar 2, 2015 at 9:57 PM, Chris Zhong <zyw@...k-chips.com> wrote:
>
> On 03/03/2015 04:50 AM, Heiko Stuebner wrote:
>>
>> Hi Chris,
>>
>> Am Montag, 9. Februar 2015, 21:12:23 schrieb Chris Zhong:
>>>
>>> The watchdog clock should be disable in dw_wdt_suspend, but we set a
>>> dummy clock to watchdog for rk3288. So the watchdog will continue to
>>> work during suspend. And we switch the system clock to 32khz from 24Mhz,
>>> during suspend, so the watchdog timer over count will increase to
>>> 755 times, about 12.5 hours, the original value is 60 seconds. So
>>> watchdog will reset the system over a night,  but voltage are all
>>> incorrect, then it hang on reset.
>>>
>>> Signed-off-by: Chris Zhong <zyw@...k-chips.com>
>>> Signed-off-by: Daniel Kurtz <djkurtz@...gle.com>
>>
>> The SGRF is not writeable in all bootmodes (I've talked with Doug about
>> this
>> to verify I remembered this correctly), so handling the sgrf gate for the
>> watchdog is not safe for all possible boards.
>>
>> Why not simply turn off the watchdog in the driver during suspend?
>
> I think SGRF is writeable, since we would set this RK3288_SGRF_SOC_CON0
> register when suspend.
> and this SGRF_PCLK_WDT_GATE is one bit of RK3288_SGRF_SOC_CON0.

OK, hmmm.  ...so I guess you're right that our current suspend/resume
code assumes that this register is writable...

I was relatively certain that SGRF was supposed to be non-accessible
in boot modes when we're running the kernel at a lower privilege
level.  I think I remember thinking that whenever someone finally
manages to implement that they would be in for quite a task dealing
with suspend/resume.  This is one thing that they'd have to deal with,
but they'd also have to deal with the fact that we program the CPU to
jump straight back to the kernel at resume time and the CPU will (as I
understand it) be in "secure SVC" mode.

...so my thought is that it's OK to add this to the suspend/resume
code and it'll just be another thing to figure out if anyone ever runs
this in a different mode.

I guess that brings up the question about whether we should revisit
(e142a4e clk: rockchip: add a dummy clock for the watchdog pclk on
rk3288) and actually try to implement it correctly.  I'm still leaning
towards leave it the way it is with the dummy clock, but if someone
wants to try implementing it for real then I suppose you could have a
nicer way to implement dw_wdt (no need for a kernel thread to keep
patting).

> I tried to set wdt_en(WDT_CR[bit 0]) to 0 in watchdog driver, but that would
> cause system reboot.

Wow, that stinks.  That explains some of the hackiness of the current
dw_wdt driver that was wondering about.  That stinks that it's totally
not documented in the user manual (unless I missed it).

With all that:

Reviewed-by: Doug Anderson <dianders@...omium.org>
Tested-by: Doug Anderson <dianders@...omium.org>
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