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

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Date:   Fri, 29 Dec 2017 08:10:19 -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:     Xiubo Li <Li.Xiubo@...escale.com>, kernel@...gutronix.de,
        Fabio Estevam <fabio.estevam@...escale.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] watchdog: imx2_wdt: restore previous timeout after
 suspend+resume

On 12/29/2017 05:59 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 setting wdog->timeout to the previous value at the end of
> the suspend function. This manual update makes wdog->timeout different
> from the actual setting in the hardware. This should be ok in our case
> as kernel code is not running while we're suspended.
> 
> Signed-off-by: Martin Kaiser <martin@...ser.cx>
> Cc: stable@...r.kernel.org

That works, though it is a bit hackish. Better would be to have a function
such as _imx2_wdt_set_timeout() which doesn't actually update wdt->timeout
and could be called from all the other places doing the same.
Separate patch, maybe.

Reviewed-by: Guenter Roeck <linux@...ck-us.net>

> ---
>   drivers/watchdog/imx2_wdt.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> index 4874b0f..66efcc0 100644
> --- a/drivers/watchdog/imx2_wdt.c
> +++ b/drivers/watchdog/imx2_wdt.c
> @@ -368,6 +368,7 @@ static int imx2_wdt_suspend(struct device *dev)
>   {
>   	struct watchdog_device *wdog = dev_get_drvdata(dev);
>   	struct imx2_wdt_device *wdev = watchdog_get_drvdata(wdog);
> +	unsigned int resume_timeout = wdog->timeout;
>   
>   	/* The watchdog IP block is running */
>   	if (imx2_wdt_is_running(wdev)) {
> @@ -377,6 +378,7 @@ static int imx2_wdt_suspend(struct device *dev)
>   
>   	clk_disable_unprepare(wdev->clk);
>   
> +	wdog->timeout = resume_timeout;
>   	return 0;
>   }
>   
>