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

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Message-ID: <5a33f86d-d82c-4685-8da7-5e623487a40c@linux.alibaba.com>
Date: Wed, 19 Feb 2025 11:41:23 +0800
From: Heyi Guo <guoheyi@...ux.alibaba.com>
To: Guenter Roeck <linux@...ck-us.net>, 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

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)).

>
>> +    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.

Thanks,

Heyi

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