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Sender: Guenter Roeck <groeck7@gmail.com>
Date: Sat, 6 Apr 2024 05:56:27 -0700
From: Guenter Roeck <linux@roeck-us.net>
To: Judith Mendez <jm@ti.com>
Cc: Wim Van Sebroeck <wim@linux-watchdog.org>,
	linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] watchdog: rti_wdt: Set min_hw_heartbeat_ms to
 accommodate 5% safety margin
Message-ID: <717195a8-84f7-4bdc-a108-efafd3ef2a46@roeck-us.net>
References: <20240403212426.582727-1-jm@ti.com>
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In-Reply-To: <20240403212426.582727-1-jm@ti.com>

On Wed, Apr 03, 2024 at 04:24:26PM -0500, Judith Mendez wrote:
> On AM62x, the watchdog is pet before the valid window
> is open. Fix min_hw_heartbeat and accommodate a 5% safety
> margin with the exception of open window size < 10%,
> which shall use <5% due to the smaller open window size.
> 
> Signed-off-by: Judith Mendez <jm@ti.com>

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

> ---
>  drivers/watchdog/rti_wdt.c | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/watchdog/rti_wdt.c b/drivers/watchdog/rti_wdt.c
> index 8e1be7ba0103..0b16ada659cc 100644
> --- a/drivers/watchdog/rti_wdt.c
> +++ b/drivers/watchdog/rti_wdt.c
> @@ -92,7 +92,7 @@ static int rti_wdt_start(struct watchdog_device *wdd)
>  	 * to be 50% or less than that; we obviouly want to configure the open
>  	 * window as large as possible so we select the 50% option.
>  	 */
> -	wdd->min_hw_heartbeat_ms = 500 * wdd->timeout;
> +	wdd->min_hw_heartbeat_ms = 550 * wdd->timeout;
>  
>  	/* Generate NMI when wdt expires */
>  	writel_relaxed(RTIWWDRX_NMI, wdt->base + RTIWWDRXCTRL);
> @@ -126,31 +126,33 @@ static int rti_wdt_setup_hw_hb(struct watchdog_device *wdd, u32 wsize)
>  	 * be petted during the open window; not too early or not too late.
>  	 * The HW configuration options only allow for the open window size
>  	 * to be 50% or less than that.
> +	 * To avoid any glitches, we accommodate 5% safety margin, with the
> +	 * exception of open window size < 10%.
>  	 */
>  	switch (wsize) {
>  	case RTIWWDSIZE_50P:
> -		/* 50% open window => 50% min heartbeat */
> -		wdd->min_hw_heartbeat_ms = 500 * heartbeat;
> +		/* 50% open window => 55% min heartbeat */
> +		wdd->min_hw_heartbeat_ms = 550 * heartbeat;
>  		break;
>  
>  	case RTIWWDSIZE_25P:
> -		/* 25% open window => 75% min heartbeat */
> -		wdd->min_hw_heartbeat_ms = 750 * heartbeat;
> +		/* 25% open window => 80% min heartbeat */
> +		wdd->min_hw_heartbeat_ms = 800 * heartbeat;
>  		break;
>  
>  	case RTIWWDSIZE_12P5:
> -		/* 12.5% open window => 87.5% min heartbeat */
> -		wdd->min_hw_heartbeat_ms = 875 * heartbeat;
> +		/* 12.5% open window => 92.5% min heartbeat */
> +		wdd->min_hw_heartbeat_ms = 925 * heartbeat;
>  		break;
>  
>  	case RTIWWDSIZE_6P25:
> -		/* 6.5% open window => 93.5% min heartbeat */
> -		wdd->min_hw_heartbeat_ms = 935 * heartbeat;
> +		/* 6.5% open window => 96.5% min heartbeat */
> +		wdd->min_hw_heartbeat_ms = 965 * heartbeat;
>  		break;
>  
>  	case RTIWWDSIZE_3P125:
> -		/* 3.125% open window => 96.9% min heartbeat */
> -		wdd->min_hw_heartbeat_ms = 969 * heartbeat;
> +		/* 3.125% open window => 97.9% min heartbeat */
> +		wdd->min_hw_heartbeat_ms = 979 * heartbeat;
>  		break;
>  
>  	default:
> -- 
> 2.43.2
> 
>