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

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Message-ID: <e692263e-a390-4611-b629-2b9feca1883a@roeck-us.net>
Date: Tue, 18 Feb 2025 22:07:16 -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 2/18/25 19:41, Heyi Guo wrote:
> Hi Guenter,
> 
> Thanks for your comments.
> 
> On 2025/2/18 13:33, 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@...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.
> It was supposed to be a straight-forward way to check if the pretimeout value is supported by the hardware. I can change to wdt->timeout if it is better.
> 
> Further, in the case of wdt->timeout > max_hw_heartbeat_ms, shall we restrict the pretimeout to be larger than wdt->timeout - max_hw_heartbeat_ms  / 2? For the watchdog_kworker works in max_hw_heartbeat_ms  / 2 interval, pretimeout event may be triggered unexpected when watchdog is not pinged in (max_hw_heartbeat_ms - (timeout - pretimeout)).
> 

The kernel internal logic should handle that. If not, it needs to be modified/fixed.

>>
>>> +    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.
> 
> watchdog_pretimeout_invalid() will return false if wdt->timeout == 0, but we can't determine the hardware pretimeout value if timeout == 0 here.
> 

Sorry, I don't understand what you mean. If watchdog_pretimeout_invalid()
returns false if timeout == 0, aspeed_wdt_set_pretimeout() won't be called.
Why does that preclude depending on it ?

On a side note, I do wonder why the driver accepts a timeout value of 0 seconds.

Guenter