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

[Guenter Roeck <linux@roeck-us.net>]

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@linux.alibaba.com>
> 
> Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Joel Stanley <joel@jms.id.au>
> Cc: Andrew Jeffery <andrew@codeconstruct.com.au>
> Cc: Eddie James <eajames@linux.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;