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Date:   Mon, 24 May 2021 09:42:09 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Douglas Anderson <dianders@chromium.org>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        linux-watchdog@vger.kernel.org, Stephen Boyd <swboyd@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH] watchdog: qcom: Move suspend/resume to
 suspend_late/resume_early
In-Reply-To: <3f76d6cc-df32-6bf3-9971-4ca8f0ee8169@roeck-us.net>
References: <20210310202004.1436-1-saiprakash.ranjan@codeaurora.org>
 <20210310202327.GA237124@roeck-us.net>
 <948130ae3a0781eb19b7431059852c23@codeaurora.org>
 <7bbfb6af534c22cd1e50f16aadd412c1@codeaurora.org>
 <3f76d6cc-df32-6bf3-9971-4ca8f0ee8169@roeck-us.net>
Message-ID: <ada92dd88c775b5140c397d4cef74f83@codeaurora.org>
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On 2021-05-24 09:33, Guenter Roeck wrote:
> On 5/23/21 7:38 PM, Sai Prakash Ranjan wrote:
>> On 2021-04-20 11:13, Sai Prakash Ranjan wrote:
>>> Hi Guenter,
>>> 
>>> On 2021-03-11 01:53, Guenter Roeck wrote:
>>>> On Thu, Mar 11, 2021 at 01:50:04AM +0530, Sai Prakash Ranjan wrote:
>>>>> During suspend/resume usecases and tests, it is common to see 
>>>>> issues
>>>>> such as lockups either in suspend path or resume path because of 
>>>>> the
>>>>> bugs in the corresponding device driver pm handling code. In such 
>>>>> cases,
>>>>> it is important that watchdog is active to make sure that we either
>>>>> receive a watchdog pretimeout notification or a bite causing reset
>>>>> instead of a hang causing us to hard reset the machine.
>>>>> 
>>>>> There are good reasons as to why we need this because:
>>>>> 
>>>>> * We can have a watchdog pretimeout governor set to panic in which
>>>>>   case we can have a backtrace which would help identify the issue
>>>>>   with the particular driver and cause a normal reboot.
>>>>> 
>>>>> * Even in case where there is no pretimeout support, a watchdog
>>>>>   bite is still useful because some firmware has debug support to 
>>>>> dump
>>>>>   CPU core context on watchdog bite for post-mortem analysis.
>>>>> 
>>>>> * One more usecase which comes to mind is of warm reboot. In case 
>>>>> we
>>>>>   hard reset the target, a cold reboot could be induced resulting 
>>>>> in
>>>>>   lose of ddr contents thereby losing all the debug info.
>>>>> 
>>>>> Currently, the watchdog pm callback just invokes the usual suspend
>>>>> and resume callback which do not have any special ordering in the
>>>>> sense that a watchdog can be suspended before the buggy device 
>>>>> driver
>>>>> suspend callback and watchdog resume can happen after the buggy 
>>>>> device
>>>>> driver resume callback. This would mean that the watchdog will not 
>>>>> be
>>>>> active when the buggy driver cause the lockups thereby hanging the
>>>>> system. So to make sure this doesn't happen, move the watchdog pm 
>>>>> to
>>>>> use late/early system pm callbacks which will ensure that the 
>>>>> watchdog
>>>>> is suspended late and resumed early so that it can catch such 
>>>>> issues.
>>>>> 
>>>>> Signed-off-by: Sai Prakash Ranjan 
>>>>> <saiprakash.ranjan@codeaurora.org>
>>>> 
>>>> Reviewed-by: Guenter Roeck <linux@roeck-us.net>
>>>> 
>>> 
>>> Gentle Ping. I don't see this in linux-next or linux-watchdog, please 
>>> let
>>> me know if anything is pending from my side.
>>> 
>> 
>> Gentle Ping !!
>> 
> 
> It is my watchdog-next branch. At some point Wim will hopefully pick it 
> up.
> 

Ah I see, thanks for the info.

-Sai

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