linux-kernel - Re: [PATCH 1/2] driver/aspeed-wdt: fix pretimeout for counting down logic

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Message-ID: <50ab5a0a-b807-4bd7-bda8-7c6f4bfc76fc@roeck-us.net>
Date: Mon, 17 Feb 2025 21:33:27 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Heyi Guo <guoheyi@...ux.alibaba.com>, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-aspeed@...ts.ozlabs.org,
 linux-kernel@...r.kernel.org, linux-watchdog@...r.kernel.org
Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>, Joel Stanley <joel@....id.au>,
 Andrew Jeffery <andrew@...econstruct.com.au>,
 Eddie James <eajames@...ux.ibm.com>
Subject: Re: [PATCH 1/2] driver/aspeed-wdt: fix pretimeout for counting down
 logic

On 2/17/25 19:16, Heyi Guo wrote:
> Aspeed watchdog uses counting down logic, so the value set to register
> should be the value of subtracting pretimeout from total timeout.
> 
> Fixes: 9ec0b7e06835 ("watchdog: aspeed: Enable pre-timeout interrupt")
> 
> Signed-off-by: Heyi Guo <guoheyi@...ux.alibaba.com>
> 
> Cc: Wim Van Sebroeck <wim@...ux-watchdog.org>
> Cc: Guenter Roeck <linux@...ck-us.net>
> Cc: Joel Stanley <joel@....id.au>
> Cc: Andrew Jeffery <andrew@...econstruct.com.au>
> Cc: Eddie James <eajames@...ux.ibm.com>
> ---
>   drivers/watchdog/aspeed_wdt.c | 7 +++++++
>   1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/watchdog/aspeed_wdt.c b/drivers/watchdog/aspeed_wdt.c
> index b4773a6aaf8c..520d8aba12a5 100644
> --- a/drivers/watchdog/aspeed_wdt.c
> +++ b/drivers/watchdog/aspeed_wdt.c
> @@ -187,6 +187,13 @@ static int aspeed_wdt_set_pretimeout(struct watchdog_device *wdd,
>   	u32 actual = pretimeout * WDT_RATE_1MHZ;
>   	u32 s = wdt->cfg->irq_shift;
>   	u32 m = wdt->cfg->irq_mask;
> +	u32 reload = readl(wdt->base + WDT_RELOAD_VALUE);
> +

It is unusual to use a register value here and not the configured timeout
value. I would have assumed that pretimeout is compared against wdt->timout,
not against the register value, and that the multiplication with WDT_RATE_1MHZ
is done after validation. This needs an explanation.

> +	if (actual >= reload)
> +		return -EINVAL;
> +

On top of that, you'll also need to explain why watchdog_pretimeout_invalid()
and with it the validation in watchdog_set_pretimeout() does not work for this
watchdog and why this extra validation is necessary.

Guenter

> +	/* watchdog timer is counting down */
> +	actual = reload - actual;
>   
>   	wdd->pretimeout = pretimeout;
>   	wdt->ctrl &= ~m;