linux-kernel - Re: [PATCH 1/2] watchdog: sbsa_wdog: Fix the timeout calculation while programming

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Date:   Tue, 7 Feb 2023 08:03:47 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     George Cherian <george.cherian@...vell.com>,
        wim@...ux-watchdog.org, zhangshaokun@...ilicon.com
Cc:     linux-watchdog@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] watchdog: sbsa_wdog: Fix the timeout calculation
 while programming

On 2/6/23 20:46, George Cherian wrote:
> The time out calculation done in sbsa_gwdt_set_timeout() would always
> return a 32-bit value. Use proper typecasting to make sure the overflow
> values are captured.
> 
> Fixes: abd3ac7902fb ("watchdog: sbsa: Support architecture version 1")
> 
> Signed-off-by: George Cherian <george.cherian@...vell.com>
> ---
>   drivers/watchdog/sbsa_gwdt.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c
> index 9791c74aebd4..aaa3f5631f29 100644
> --- a/drivers/watchdog/sbsa_gwdt.c
> +++ b/drivers/watchdog/sbsa_gwdt.c
> @@ -152,14 +152,14 @@ static int sbsa_gwdt_set_timeout(struct watchdog_device *wdd,
>   	wdd->timeout = timeout;
>   
>   	if (action)
> -		sbsa_gwdt_reg_write(gwdt->clk * timeout, gwdt);
> +		sbsa_gwdt_reg_write((u64)gwdt->clk * (u64)timeout, gwdt);
>   	else
>   		/*
>   		 * In the single stage mode, The first signal (WS0) is ignored,
>   		 * the timeout is (WOR * 2), so the WOR should be configured
>   		 * to half value of timeout.
>   		 */
> -		sbsa_gwdt_reg_write(gwdt->clk / 2 * timeout, gwdt);
> +		sbsa_gwdt_reg_write((u64)gwdt->clk / 2 * (u64)timeout, gwdt);
>   
>   	return 0;
>   }

The driver sets max_hw_heartbeat_ms. It is its responsibility to clamp
the timeout value written into the controller to the configured limit
to avoid confusing the watchdog core. Something like

	timeout = clamp(timeout, 0, wdd->max_hw_heartbeat_ms / 1000);

This also solves the problem in patch 2 since it guarantees that the
resulting register value is <= U32_MAX for version 0.

Guenter