linux-kernel - Re: [PATCH 4/10] watchdog: bcm63xx_wdt: Handle hardware interrupt and remove software timer

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Message-ID: <56561A0B.9020700@simon.arlott.org.uk>
Date:	Wed, 25 Nov 2015 20:28:59 +0000
From:	Simon Arlott <simon@...e.lp0.eu>
To:	Jonas Gorski <jogo@...nwrt.org>, Guenter Roeck <linux@...ck-us.net>
Cc:	Florian Fainelli <f.fainelli@...il.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <marc.zyngier@....com>,
	Kevin Cernekee <cernekee@...il.com>,
	Wim Van Sebroeck <wim@...ana.be>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	MIPS Mailing List <linux-mips@...ux-mips.org>,
	linux-watchdog@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>
Subject: Re: [PATCH 4/10] watchdog: bcm63xx_wdt: Handle hardware interrupt and
 remove software timer

On 25/11/15 20:14, Jonas Gorski wrote:
> On Tue, Nov 24, 2015 at 7:21 PM, Guenter Roeck <linux@...ck-us.net> wrote:
>> On Sun, Nov 22, 2015 at 02:05:16PM +0000, Simon Arlott wrote:
>>> There is a level triggered interrupt for the watchdog timer as part of
>>> the bcm63xx_timer device. The interrupt occurs when the hardware watchdog
>>> timer reaches 50% of the remaining time.
>>>
>>> It is not possible to mask the interrupt within the bcm63xx_timer device.
>>> To get around this limitation, handle the interrupt by restarting the
>>> watchdog with the current remaining time (which will be half the previous
>>> timeout) so that the interrupt occurs again at 1/4th, 1/8th, etc. of the
>>> original timeout value until the watchdog forces a reboot.
>>>
>>> The software timer was restarting the hardware watchdog with a 85 second
>>> timeout until the software timer expired, and then causing a panic()
>>> about 42.5 seconds later when the hardware interrupt occurred. The
>>> hardware watchdog would not reboot until a further 42.5 seconds had
>>> passed.
>>>
>>> Remove the software timer and rely on the hardware timer directly,
>>> reducing the maximum timeout from 256 seconds to 85 seconds
>>> (2^32 / WDT_HZ).
>>>
>>
>> Florian,
>>
>> can you have a look into this patch and confirm that there is no better
>> way to clear the interrupt status ?
> 
> While the watchdog interrupt can't be masked, it should be able to be
> cleared by writing 1 to the appropriate bit in the timer block's
> interrupt status register. At least the broadcom sources do so.

Not according to the hardware itself:
[    6.674626] watchdog watchdog0: warning timer fired, reboot in 7499ms
[    6.681212] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[    6.688583] watchdog watchdog0: warning timer fired, reboot in 7486ms
[    6.695181] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[    6.702554] watchdog watchdog0: warning timer fired, reboot in 7472ms
[    6.709158] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[    6.716529] watchdog watchdog0: warning timer fired, reboot in 7458ms
[    6.723135] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[    6.730538] watchdog watchdog0: warning timer fired, reboot in 7444ms
[    6.737121] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08
[    6.744482] watchdog watchdog0: warning timer fired, reboot in 7430ms
[    6.751090] irq_bcm6345_l2_timer: bcm6345_timer_write_int_status: b0000083=08


typedef struct Timer {
    uint16        unused0;
    byte          TimerMask;
#define TIMER0EN        0x01
#define TIMER1EN        0x02
#define TIMER2EN        0x04
    byte          TimerInts;
#define TIMER0          0x01
#define TIMER1          0x02
#define TIMER2          0x04
#define WATCHDOG        0x08
...

-- 
Simon Arlott
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