Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Sender: Guenter Roeck <groeck7@gmail.com>
Subject: Re: [PATCH v1] watchdog: imx2_wdt: clear WDOG_HW_RUNNING before
 suspend
To:     Robin Gong <yibin.gong@nxp.com>, wim@linux-watchdog.org,
        shawnguo@kernel.org, s.hauer@pengutronix.de, festevam@gmail.com
Cc:     linux-imx@nxp.com, kernel@pengutronix.de,
        linux-watchdog@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
References: <1620732032-7675-1-git-send-email-yibin.gong@nxp.com>
From:   Guenter Roeck <linux@roeck-us.net>
Message-ID: <d5364293-8cba-0d39-aa45-a55c5d6d2af6@roeck-us.net>
Date:   Mon, 10 May 2021 20:59:25 -0700
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101
 Thunderbird/78.7.1
MIME-Version: 1.0
In-Reply-To: <1620732032-7675-1-git-send-email-yibin.gong@nxp.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 5/11/21 4:20 AM, Robin Gong wrote:
> Since watchdog_ping_work is not freezable so that it maybe scheduled before
> imx2_wdt_resume where watchdog clock enabled, hence, kernel will hang in
> imx2_wdt_ping without clock, and then watchdog reset happen. Prevent the
> above case by clearing WDOG_HW_RUNNING before suspend, and restore it with
> ping in imx2_wdt_resume.
> 
> Signed-off-by: Robin Gong <yibin.gong@nxp.com>
> ---
>   drivers/watchdog/imx2_wdt.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> index b84f80f..d3751e9 100644
> --- a/drivers/watchdog/imx2_wdt.c
> +++ b/drivers/watchdog/imx2_wdt.c
> @@ -357,6 +357,13 @@ static int __maybe_unused imx2_wdt_suspend(struct device *dev)
>   		 */
>   		__imx2_wdt_set_timeout(wdog, IMX2_WDT_MAX_TIME);
>   		imx2_wdt_ping(wdog);
> +
> +		/*
> +		 * clear WDOG_HW_RUNNING to prevent watchdog_ping_work running
> +		 * before imx2_wdt_resume where clock enabled, otherwise kernel
> +		 * will hang and watchdog reset happen then.
> +		 */
> +		clear_bit(WDOG_HW_RUNNING, &wdog->status);
>   	}
>   
>   	clk_disable_unprepare(wdev->clk);
> @@ -386,6 +393,7 @@ static int __maybe_unused imx2_wdt_resume(struct device *dev)
>   	if (imx2_wdt_is_running(wdev)) {
>   		imx2_wdt_set_timeout(wdog, wdog->timeout);
>   		imx2_wdt_ping(wdog);
> +		set_bit(WDOG_HW_RUNNING, &wdog->status);
>   	}
>   
>   	return 0;
> 
I really don't like this; it depends on assumptions how the watchdog
core works, and it misuses WDOG_HW_RUNNING to indicate that the clock
is stopped (or that the driver is in suspend mode).

If ping doesn't work with the clock stopped, I think it would be much
better to have a flag indicating that the clock is stopped, and have
the ping function do nothing if it is called with stopped clock
(ie if suspended).

Guenter