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

[Guenter Roeck]

On 2/18/25 17:25, Andrew Jeffery wrote:
> On Mon, 2025-02-17 at 21:33 -0800, Guenter Roeck wrote:
>> 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 at linux.alibaba.com>
>>>
>>> Cc: Wim Van Sebroeck <wim at linux-watchdog.org>
>>> Cc: Guenter Roeck <linux at roeck-us.net>
>>> Cc: Joel Stanley <joel at jms.id.au>
>>> Cc: Andrew Jeffery <andrew at codeconstruct.com.au>
>>> Cc: Eddie James <eajames at 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.
> 
> +1
> 
>>
>>> +       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.
> 
> +1 as well.
> 
> Further, the logic looks broken regardless for the AST2400 where
> there's no pretimeout support. aspeed_wdt_set_pretimeout() should error
> out if wdt->cfg->irq_mask is 0.
> 

It should not register as supporting pretimeout in the first place.

Guenter