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Date:   Mon, 24 May 2021 08:08:39 +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: <948130ae3a0781eb19b7431059852c23@codeaurora.org>
References: <20210310202004.1436-1-saiprakash.ranjan@codeaurora.org>
 <20210310202327.GA237124@roeck-us.net>
 <948130ae3a0781eb19b7431059852c23@codeaurora.org>
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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 !!

Thanks,
Sai
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