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

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Message-ID: <CAOiHx=kn4NPxxYq0Te_T+8y_Cb1udyU0_EO-_eKp2Xshh7X6EA@mail.gmail.com>
Date:	Wed, 25 Nov 2015 21:14:13 +0100
From:	Jonas Gorski <jogo@...nwrt.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Simon Arlott <simon@...e.lp0.eu>,
	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 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.


Jonas
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