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Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH] watchdog: qcom: Move suspend/resume to
 suspend_late/resume_early
To:     Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>
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>
References: <20210310202004.1436-1-saiprakash.ranjan@codeaurora.org>
 <20210310202327.GA237124@roeck-us.net>
 <948130ae3a0781eb19b7431059852c23@codeaurora.org>
 <7bbfb6af534c22cd1e50f16aadd412c1@codeaurora.org>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <3f76d6cc-df32-6bf3-9971-4ca8f0ee8169@roeck-us.net>
Date:   Sun, 23 May 2021 21:03:20 -0700
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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.

Guenter