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SubjectRe: [PATCH] watchdog: qcom: Move suspend/resume to suspend_late/resume_early
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>

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