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

From: Guenter Roeck <linux@roeck-us.net>
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
Subject: Re: [PATCH] watchdog: qcom: Move suspend/resume to suspend_late/resume_early
Date: Wed, 10 Mar 2021 12:23:27 -0800	[thread overview]
Message-ID: <20210310202327.GA237124@roeck-us.net> (raw)
In-Reply-To: <20210310202004.1436-1-saiprakash.ranjan@codeaurora.org>

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>

> ---
>  drivers/watchdog/qcom-wdt.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/watchdog/qcom-wdt.c b/drivers/watchdog/qcom-wdt.c
> index e38a87ffe5f5..0d2209c5eaca 100644
> --- a/drivers/watchdog/qcom-wdt.c
> +++ b/drivers/watchdog/qcom-wdt.c
> @@ -329,7 +329,9 @@ static int __maybe_unused qcom_wdt_resume(struct device *dev)
>  	return 0;
>  }
>  
> -static SIMPLE_DEV_PM_OPS(qcom_wdt_pm_ops, qcom_wdt_suspend, qcom_wdt_resume);
> +static const struct dev_pm_ops qcom_wdt_pm_ops = {
> +	SET_LATE_SYSTEM_SLEEP_PM_OPS(qcom_wdt_suspend, qcom_wdt_resume)
> +};
>  
>  static const struct of_device_id qcom_wdt_of_table[] = {
>  	{ .compatible = "qcom,kpss-timer", .data = &match_data_apcs_tmr },
> -- 
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