linux-kernel - Re: [PATCH V2 1/3] watchdog: imgpdc: Allow timeout to be set in device-tree

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Date:	Wed, 1 Apr 2015 23:22:18 +0100
From:	James Hogan <james.hogan@...tec.com>
To:	Andrew Bresticker <abrestic@...omium.org>
CC:	Wim Van Sebroeck <wim@...ana.be>,
	Guenter Roeck <linux@...ck-us.net>,
	<linux-watchdog@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"Ezequiel Garcia" <ezequiel.garcia@...tec.com>
Subject: Re: [PATCH V2 1/3] watchdog: imgpdc: Allow timeout to be set in
 device-tree

Hi Andrew,

On Wed, Apr 01, 2015 at 10:43:14AM -0700, Andrew Bresticker wrote:
> Since the heartbeat is statically initialized to its default value,
> watchdog_init_timeout() will never look in the device-tree for a
> timeout-sec value.  Instead of statically initializing heartbeat,
> fall back to the default timeout value if watchdog_init_timeout()
> fails.

Whoops. Sorry about that. I wasn't aware that a timeout-sec value was
expected. It isn't mentioned in the DT binding documentation for this
device :-(.

> 
> Signed-off-by: Andrew Bresticker <abrestic@...omium.org>
> Cc: Ezequiel Garcia <ezequiel.garcia@...tec.com>
> Cc: James Hogan <james.hogan@...tec.com>
> ---
> New for v2.
> ---
>  drivers/watchdog/imgpdc_wdt.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/watchdog/imgpdc_wdt.c b/drivers/watchdog/imgpdc_wdt.c
> index 0deaa4f..89b2abc 100644
> --- a/drivers/watchdog/imgpdc_wdt.c
> +++ b/drivers/watchdog/imgpdc_wdt.c
> @@ -42,7 +42,7 @@
>  #define PDC_WDT_MIN_TIMEOUT		1
>  #define PDC_WDT_DEF_TIMEOUT		64
>  
> -static int heartbeat = PDC_WDT_DEF_TIMEOUT;
> +static int heartbeat;
>  module_param(heartbeat, int, 0);
>  MODULE_PARM_DESC(heartbeat, "Watchdog heartbeats in seconds "
>  	"(default=" __MODULE_STRING(PDC_WDT_DEF_TIMEOUT) ")");
> @@ -195,9 +195,9 @@ static int pdc_wdt_probe(struct platform_device *pdev)
>  
>  	ret = watchdog_init_timeout(&pdc_wdt->wdt_dev, heartbeat, &pdev->dev);
>  	if (ret < 0) {
> -		pdc_wdt->wdt_dev.timeout = pdc_wdt->wdt_dev.max_timeout;
> +		pdc_wdt->wdt_dev.timeout = PDC_WDT_DEF_TIMEOUT;

The watchdog_init_timeout kerneldoc comment suggests that the old value
should be the default timeout, i.e. that timeout should be set to
PDC_WDT_DEF_TIMEOUT before calling watchdog_init_timeout, rather than
whenever ret < 0.

Indeed, if heartbeat is set to an invalid non-zero value,
watchdog_init_timeout will still try and set timeout from DT, but also
still returns -EINVAL regardless of whether that succeeds, and this
would incorrectly override the timeout from DT with the hardcoded
default.

>  		dev_warn(&pdev->dev,
> -			 "Initial timeout out of range! setting max timeout\n");
> +			 "Initial timeout out of range! setting default timeout\n");

It feels wrong for a presumably safe & normal situation (i.e. no default
in DT, which arguably shouldn't contain policy anyway) to show a
warning, but it can also show due to an invalid module parameter (or
invalid DT property) which is most definitely justified.

The caller can check (ret < 0 && heartbeat) to tell if heartbeat was
invalid, but unfortunately it can't easily tell if the DT property is
out of range rather than simply absent.

Cheers
James

>  	}
>  
>  	pdc_wdt_stop(&pdc_wdt->wdt_dev);
> -- 
> 2.2.0.rc0.207.ga3a616c
> 

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