linux-kernel - Re: [PATCH v2] watchdog: iTCO_wdt: Account for rebooting on second timeout

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Date:   Mon, 31 May 2021 10:27:53 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Wim Van Sebroeck <wim@...ux-watchdog.org>,
        linux-watchdog@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Christian Storm <christian.storm@...mens.com>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [PATCH v2] watchdog: iTCO_wdt: Account for rebooting on second
 timeout

On 30.05.21 15:19, Guenter Roeck wrote:
> On Sun, May 30, 2021 at 01:24:23PM +0200, Jan Kiszka wrote:
>> From: Jan Kiszka <jan.kiszka@...mens.com>
>>
>> This was already attempted to fix via 1fccb73011ea: If the BIOS did not
>> enable TCO SMIs, the timer definitely needs to trigger twice in order to
>> cause a reboot. If TCO SMIs are on, as well as SMIs in general, we can
>> continue to assume that the BIOS will perform a reboot on the first
>> timeout.
>>
>> QEMU with its ICH9 and related BIOS falls into the former category,
>> currently taking twice the configured timeout in order to reboot the
>> machine. For iTCO version that fall under turn_SMI_watchdog_clear_off,
>> this is also true and was currently only addressed for v1, irrespective
>> of the turn_SMI_watchdog_clear_off value.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
>> ---
>>
>> Changes in v2:
>>  - consider GBL_SMI_EN as well
>>
>>  drivers/watchdog/iTCO_wdt.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/watchdog/iTCO_wdt.c b/drivers/watchdog/iTCO_wdt.c
>> index bf31d7b67a69..3f1324871cfd 100644
>> --- a/drivers/watchdog/iTCO_wdt.c
>> +++ b/drivers/watchdog/iTCO_wdt.c
>> @@ -71,6 +71,8 @@
>>  #define TCOBASE(p)	((p)->tco_res->start)
>>  /* SMI Control and Enable Register */
>>  #define SMI_EN(p)	((p)->smi_res->start)
>> +#define TCO_EN		(1 << 13)
>> +#define GBL_SMI_EN	(1 << 0)
>>  
>>  #define TCO_RLD(p)	(TCOBASE(p) + 0x00) /* TCO Timer Reload/Curr. Value */
>>  #define TCOv1_TMR(p)	(TCOBASE(p) + 0x01) /* TCOv1 Timer Initial Value*/
>> @@ -355,8 +357,12 @@ static int iTCO_wdt_set_timeout(struct watchdog_device *wd_dev, unsigned int t)
>>  
>>  	tmrval = seconds_to_ticks(p, t);
>>  
>> -	/* For TCO v1 the timer counts down twice before rebooting */
>> -	if (p->iTCO_version == 1)
>> +	/*
>> +	 * If TCO SMIs are off, the timer counts down twice before rebooting.
>> +	 * Otherwise, the BIOS generally reboots when the SMI triggers.
>> +	 */
>> +	if (p->smi_res &&
>> +	    (SMI_EN(p) & (TCO_EN | GBL_SMI_EN)) != (TCO_EN | GBL_SMI_EN))
>>  		tmrval /= 2;
> 
> This expands the scope of this adjustment to all versions, while at the same
> time making it conditional for v1. Is this correct ? What for systems with v1
> TCO where the above conditions are not met ?

Yes, this is intended. You find the reference to "reboots on second
timeout" even in latest EHL datasheets (v6).

Jan

> 
> Guenter
> 
>>  
>>  	/* from the specs: */
>> @@ -521,7 +527,7 @@ static int iTCO_wdt_probe(struct platform_device *pdev)
>>  		 * Disables TCO logic generating an SMI#
>>  		 */
>>  		val32 = inl(SMI_EN(p));
>> -		val32 &= 0xffffdfff;	/* Turn off SMI clearing watchdog */
>> +		val32 &= ~TCO_EN;	/* Turn off SMI clearing watchdog */
>>  		outl(val32, SMI_EN(p));
>>  	}
>>  
>> -- 
>> 2.26.2

-- 
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