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

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Message-ID: <4e407c28-ab9e-7093-49f4-f9b985269fdc@siemens.com>
Date:   Mon, 31 May 2021 11:18:07 +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 31.05.21 10:27, Jan Kiszka wrote:
> 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).
> 

To make it clearer: By default, we disabled SMIs on v1, thus had to
adjust the timeout there unconditionally. In QEMU (v2), the firmware
does not enable SMI, and we failed to handle that. Conceptually, any
platform on any (known) version that does not use TCO SMIs is affected.

Jan

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