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References: <20210310202004.1436-1-saiprakash.ranjan@codeaurora.org>
In-Reply-To: <20210310202004.1436-1-saiprakash.ranjan@codeaurora.org>
From:   Doug Anderson <dianders@chromium.org>
Date:   Wed, 10 Mar 2021 12:27:01 -0800
Message-ID: <CAD=FV=X-nZu1VTJdLOiXmtC4HrnK85KK=KqYe-9szX2LiJoo-Q@mail.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>,
        Guenter Roeck <linux@roeck-us.net>,
        Wim Van Sebroeck <wim@linux-watchdog.org>,
        linux-watchdog@vger.kernel.org, Stephen Boyd <swboyd@chromium.org>,
        Matthias Kaehlcke <mka@chromium.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-arm-msm <linux-arm-msm@vger.kernel.org>
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Hi,

On Wed, Mar 10, 2021 at 12:20 PM Sai Prakash Ranjan
<saiprakash.ranjan@codeaurora.org> 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>
> ---
>  drivers/watchdog/qcom-wdt.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)

Reviewed-by: Douglas Anderson <dianders@chromium.org>