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From: Jonas Gorski <jogo@openwrt.org>
Date: Wed, 25 Nov 2015 21:14:13 +0100
Message-ID: <CAOiHx=kn4NPxxYq0Te_T+8y_Cb1udyU0_EO-_eKp2Xshh7X6EA@mail.gmail.com>
Subject: Re: [PATCH 4/10] watchdog: bcm63xx_wdt: Handle hardware interrupt and
 remove software timer
To: Guenter Roeck <linux@roeck-us.net>
Cc: Simon Arlott <simon@fire.lp0.eu>, Florian Fainelli <f.fainelli@gmail.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Ralf Baechle <ralf@linux-mips.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Jason Cooper <jason@lakedaemon.net>,
        Marc Zyngier <marc.zyngier@arm.com>,
        Kevin Cernekee <cernekee@gmail.com>, Wim Van Sebroeck <wim@iguana.be>,
        Maxime Bizon <mbizon@freebox.fr>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        MIPS Mailing List <linux-mips@linux-mips.org>,
        linux-watchdog@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>
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On Tue, Nov 24, 2015 at 7:21 PM, Guenter Roeck <linux@roeck-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.


Jonas
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