linux-kernel - Re: [PATCH v2] watchdog: imx2_wdt: restore previous timeout after suspend+resume

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Date:   Sun, 31 Dec 2017 06:43:55 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Martin Kaiser <martin@...ser.cx>, Wim Van Sebroeck <wim@...ana.be>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     kernel@...gutronix.de, Fabio Estevam <fabio.estevam@...escale.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH v2] watchdog: imx2_wdt: restore previous timeout after
 suspend+resume

Hi Martin,

On 12/31/2017 03:17 AM, Martin Kaiser wrote:
> When the watchdog device is suspended, its timeout is set to the maximum
> value. During resume, the previously set timeout should be restored.
> This does not work at the moment.
> 
> The suspend function calls
> 
> imx2_wdt_set_timeout(wdog, IMX2_WDT_MAX_TIME);
> 
> and resume reverts this by calling
> 
> imx2_wdt_set_timeout(wdog, wdog->timeout);
> 
> However, imx2_wdt_set_timeout() updates wdog->timeout. Therefore,
> wdog->timeout is set to IMX2_WDT_MAX_TIME when we enter the resume
> function.
> 
> Fix this by adding a new function __imx2_wdt_set_timeout() which
> only updates the hardware settings. imx2_wdt_set_timeout() now calls
> __imx2_wdt_set_timeout() and then saves the new timeout to
> wdog->timeout.
> 
> During suspend, we call __imx2_wdt_set_timeout() directly so that
> wdog->timeout won't be updated and we can restore the previous value
> during resume. This approach makes wdog->timeout different from the
> actual setting in the hardware which is usually not a good thing.
> However, the two differ only while we're suspended and no kernel code is
> running, so it should be ok in this case.
> 
> Signed-off-by: Martin Kaiser <martin@...ser.cx>
> Cc: stable@...r.kernel.org
> ---
> changes in v2:
>   helper function that updates the hw settings, as per Guenter's proposal
> 
>   drivers/watchdog/imx2_wdt.c | 23 +++++++++++++++++++----
>   1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> index 4874b0f..b0c2bca 100644
> --- a/drivers/watchdog/imx2_wdt.c
> +++ b/drivers/watchdog/imx2_wdt.c
> @@ -169,18 +169,29 @@ static int imx2_wdt_ping(struct watchdog_device *wdog)
>   	return 0;
>   }
>   
> -static int imx2_wdt_set_timeout(struct watchdog_device *wdog,
> +static int __imx2_wdt_set_timeout(struct watchdog_device *wdog,
>   				unsigned int new_timeout)

Please align the continuation line with '('.
Also, the function type should be void (always returning 0 and checking
that return value does not add any value).

Thanks,
Guenter

>   {
>   	struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
>   
> -	wdog->timeout = new_timeout;
> -
>   	regmap_update_bits(wdev->regmap, IMX2_WDT_WCR, IMX2_WDT_WCR_WT,
>   			   WDOG_SEC_TO_COUNT(new_timeout));
>   	return 0;
>   }
>   
> +static int imx2_wdt_set_timeout(struct watchdog_device *wdog,
> +				unsigned int new_timeout)
> +{
> +	int ret;
> +
> +	ret = __imx2_wdt_set_timeout(wdog, new_timeout);
> +	if (ret < 0)
> +		return ret;
> +
> +	wdog->timeout = new_timeout;
> +	return 0;
> +}
> +
>   static int imx2_wdt_set_pretimeout(struct watchdog_device *wdog,
>   				   unsigned int new_pretimeout)
>   {
> @@ -371,7 +382,11 @@ static int imx2_wdt_suspend(struct device *dev)
>   
>   	/* The watchdog IP block is running */
>   	if (imx2_wdt_is_running(wdev)) {
> -		imx2_wdt_set_timeout(wdog, IMX2_WDT_MAX_TIME);
> +		/*
> +		 * Don't update wdog->timeout, we'll restore the current value
> +		 * during resume.
> +		 */
> +		__imx2_wdt_set_timeout(wdog, IMX2_WDT_MAX_TIME);
>   		imx2_wdt_ping(wdog);
>   	}
>   
>