linux-kernel - Re: [PATCH V2 2/3] watchdog: stm32: update return values recommended by watchdog kernel api

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Message-ID: <20190502202352.GB27894@roeck-us.net>
Date:   Thu, 2 May 2019 13:23:52 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Ludovic Barre <ludovic.Barre@...com>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Rob Herring <robh+dt@...nel.org>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        linux-watchdog@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org,
        linux-stm32@...md-mailman.stormreply.com
Subject: Re: [PATCH V2 2/3] watchdog: stm32: update return values recommended
 by watchdog kernel api

On Thu, May 02, 2019 at 04:08:45PM +0200, Ludovic Barre wrote:
> From: Ludovic Barre <ludovic.barre@...com>
> 
> This patch updates return values on watchdog-kernel-api.txt:
> return 0 on succes, -EINVAL for "parameter out of range"
> and -EIO for "could not write value to the watchdog".
> 
> Signed-off-by: Ludovic Barre <ludovic.barre@...com>
> ---
>  drivers/watchdog/stm32_iwdg.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/watchdog/stm32_iwdg.c b/drivers/watchdog/stm32_iwdg.c
> index e191bd8..f19a6d4 100644
> --- a/drivers/watchdog/stm32_iwdg.c
> +++ b/drivers/watchdog/stm32_iwdg.c
> @@ -81,7 +81,6 @@ static int stm32_iwdg_start(struct watchdog_device *wdd)
>  	struct stm32_iwdg *wdt = watchdog_get_drvdata(wdd);
>  	u32 val = FLAG_PVU | FLAG_RVU;
>  	u32 reload;
> -	int ret;
>  
>  	dev_dbg(wdd->parent, "%s\n", __func__);
>  
> @@ -98,13 +97,11 @@ static int stm32_iwdg_start(struct watchdog_device *wdd)
>  	reg_write(wdt->regs, IWDG_KR, KR_KEY_ENABLE);
>  
>  	/* wait for the registers to be updated (max 100ms) */
> -	ret = readl_relaxed_poll_timeout(wdt->regs + IWDG_SR, val,
> -					 !(val & (FLAG_PVU | FLAG_RVU)),
> -					 SLEEP_US, TIMEOUT_US);
> -	if (ret) {
> -		dev_err(wdd->parent,
> -			"Fail to set prescaler or reload registers\n");
> -		return ret;
> +	if (readl_relaxed_poll_timeout(wdt->regs + IWDG_SR, val,
> +				       !(val & (FLAG_PVU | FLAG_RVU)),
> +				       SLEEP_US, TIMEOUT_US)) {
> +		dev_err(wdd->parent, "Fail to set prescaler, reload regs\n");
> +		return -EIO;

Please don't. Overriding error values tends to result in complaints by
static analyzers, and we don't want to have to deal with those.

>  	}
>  
>  	/* reload watchdog */
> @@ -128,8 +125,16 @@ static int stm32_iwdg_ping(struct watchdog_device *wdd)
>  static int stm32_iwdg_set_timeout(struct watchdog_device *wdd,
>  				  unsigned int timeout)
>  {
> +	unsigned int tout = clamp(timeout, wdd->min_timeout,
> +				  wdd->max_hw_heartbeat_ms / 1000);
> +
>  	dev_dbg(wdd->parent, "%s timeout: %d sec\n", __func__, timeout);
>  
> +	if (tout != timeout) {
> +		dev_err(wdd->parent, "parameter out of range\n");
> +		return -EINVAL;
> +	}

This is simply wrong. The whole point of max_hw_heartbeat_ms is to
enable situations where the selected timeout is larger than the
timeout supported by the hardware. In that situation, the kernel
pings the hardware until the next ping from userspace is due.

> +
>  	wdd->timeout = timeout;
>  
>  	if (watchdog_active(wdd))
> -- 
> 2.7.4
>