linux-kernel - Re: [PATCH] watchdog: imx2_wdt: fix min() calculation in imx2_wdt_set

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Date:   Mon, 12 Aug 2019 06:28:05 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>
Cc:     Georg Hofmann <georg@...mannsweb.com>,
        linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] watchdog: imx2_wdt: fix min() calculation in
 imx2_wdt_set_timeout

On 8/12/19 6:13 AM, Rasmus Villemoes wrote:
> Converting from ms to s requires dividing by 1000, not multiplying. So
> this is currently taking the smaller of new_timeout and 1.28e8,
> i.e. effectively new_timeout.
> 
> The driver knows what it set max_hw_heartbeat_ms to, so use that
> value instead of doing a division at run-time.
> 
> FWIW, this can easily be tested by booting into a busybox shell and
> doing "watchdog -t 5 -T 130 /dev/watchdog" - without this patch, the
> watchdog fires after 130&127 == 2 seconds.
> 
> Fixes: b07e228eee69 "watchdog: imx2_wdt: Fix set_timeout for big timeout values"
> Cc: stable@...r.kernel.org # 5.2 plus anything the above got backported to
> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>

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

> ---
> This should really be handled in the watchdog core for any driver that
> reports max_hw_heartbeat_ms.
> 
Good point. I'll see if I can write a patch.

Guenter

> The same pattern appears in aspeed_wdt.c. I don't have the hardware, but
> s#wdd->max_hw_heartbeat_ms * 1000#WDT_MAX_TIMEOUT_MS/1000U# should fix that one.
> 
> 
>   drivers/watchdog/imx2_wdt.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/imx2_wdt.c b/drivers/watchdog/imx2_wdt.c
> index 32af3974e6bb..8d019a961ccc 100644
> --- a/drivers/watchdog/imx2_wdt.c
> +++ b/drivers/watchdog/imx2_wdt.c
> @@ -55,7 +55,7 @@
>   
>   #define IMX2_WDT_WMCR		0x08		/* Misc Register */
>   
> -#define IMX2_WDT_MAX_TIME	128
> +#define IMX2_WDT_MAX_TIME	128U
>   #define IMX2_WDT_DEFAULT_TIME	60		/* in seconds */
>   
>   #define WDOG_SEC_TO_COUNT(s)	((s * 2 - 1) << 8)
> @@ -180,7 +180,7 @@ static int imx2_wdt_set_timeout(struct watchdog_device *wdog,
>   {
>   	unsigned int actual;
>   
> -	actual = min(new_timeout, wdog->max_hw_heartbeat_ms * 1000);
> +	actual = min(new_timeout, IMX2_WDT_MAX_TIME);
>   	__imx2_wdt_set_timeout(wdog, actual);
>   	wdog->timeout = new_timeout;
>   	return 0;
>