[PATCH] watchdog: fix watchdog_set_timeout breakage for drivers like imxwd

[Sascha Hauer]

On Tue, Aug 18, 2020 at 03:18:16PM +0200, Ahmad Fatoum wrote:
> Commit 0b944fce55f4 ("watchdog: permit `wd 0` for non-stoppable, but
> inactive, watchdogs") silently broke use of non-stoppable, but inactive,
> watchdogs altogether. Because those always had watchdog_hw_running
> evaluating to false, it early exited without a chance to ever actually
> set the timeout (and for watchdog_hw_running to evaluate to != false).
> 
> This results in following watchdog drivers being broken in v2020.08.0:
> 
>  - imxwd
>  - f71808e_wdt
>  - at91sam9_wdt
> 
> Fixes: 0b944fce55f4 ("watchdog: permit `wd 0` for non-stoppable, but inactive, watchdogs")
> Reported-by: Bastian Krause <bst at pengutronix.de>
> Signed-off-by: Ahmad Fatoum <a.fatoum at pengutronix.de>
> ---
> Please apply to master (and to v2020.08.1?).
> ---
>  drivers/watchdog/wd_core.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/watchdog/wd_core.c b/drivers/watchdog/wd_core.c
> index ab1dcaa40a3a..4247288dbd0a 100644
> --- a/drivers/watchdog/wd_core.c
> +++ b/drivers/watchdog/wd_core.c
> @@ -45,12 +45,11 @@ int watchdog_set_timeout(struct watchdog *wd, unsigned timeout)
>  	if (timeout > wd->timeout_max)
>  		return -EINVAL;
>  
> -	if (watchdog_hw_running(wd) == false)
> -		return 0;
> -
>  	pr_debug("setting timeout on %s to %ds\n", watchdog_name(wd), timeout);
>  
>  	ret = wd->set_timeout(wd, timeout);
> +	if (ret == -ENOSYS && watchdog_hw_running(wd) == false)

Instead of testing for a specific error code from set_timeout(), can't
we just do a

	if (!timeout && !watchdog_hw_running(wd))
		return 0;

This would make the intention of the code more clear.

Sascha

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