linux-kernel - Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver

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Date:	Wed, 16 Sep 2015 09:57:41 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Fu Wei <fu.wei@...aro.org>
Cc:	Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
	linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
	Wei Fu <tekkamanninja@...il.com>,
	G Gregory <graeme.gregory@...aro.org>,
	Al Stone <al.stone@...aro.org>, Arnd Bergmann <arnd@...db.de>,
	Guenter Roeck <linux@...ck-us.net>,
	Vipul Gandhi <vgandhi@...eaurora.org>,
	Wim Van Sebroeck <wim@...ana.be>,
	Jon Masters <jcm@...hat.com>, Leo Duran <leo.duran@....com>,
	Jon Corbet <corbet@....net>,
	Mark Rutland <mark.rutland@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Rafael Wysocki <rjw@...ysocki.net>,
	Pratyush Anand <panand@...hat.com>
Subject: Re: [PATCH v7 5/8] Watchdog: introduce ARM SBSA watchdog driver

> >> diff --git a/drivers/watchdog/sbsa_gwdt.c b/drivers/watchdog/sbsa_gwdt.c
> >> new file mode 100644
> >> index 0000000..7ae45cc
> >> --- /dev/null
> >> +++ b/drivers/watchdog/sbsa_gwdt.c
> >> @@ -0,0 +1,459 @@
> >> +/*
> >> + * SBSA(Server Base System Architecture) Generic Watchdog driver
> >> + *
> >> + * Copyright (c) 2015, Linaro Ltd.
> >> + * Author: Fu Wei <fu.wei@...aro.org>
> >> + *         Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>
> >> + *
> >> + * This program is free software; you can redistribute it and/or modify
> >> + * it under the terms of the GNU General Public License 2 as published
> >> + * by the Free Software Foundation.
> >> + *
> >> + * This program is distributed in the hope that it will be useful,
> >> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> >> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> >> + * GNU General Public License for more details.
> >> + *
> >> + * The SBSA Generic watchdog driver is compatible with the pretimeout
> >> + * concept of Linux kernel.
> >> + * The timeout and pretimeout are determined by WCV or WOR.
> >> + * The first watch period is set by writing WCV directly, that can
> >> + * support more than 10s timeout at the maximum system counter
> >> + * frequency (400MHz).
> >> + * When WS0 is triggered, the second watch period (pretimeout) is
> >> + * determined by one of these registers:
> >> + * (1)WOR: 32bit register, this gives a maximum watch period of
> >> + * around 10s at the maximum system counter frequency. It's loaded
> >> + * automatically by hardware.
> >> + * (2)WCV: If the pretimeout value is greater then "max_wor_timeout",
> >> + * it will be loaded in WS0 interrupt routine. If system is in
> >> + * ws0_mode (reboot by kexec/kdump in panic with watchdog enabled
> >> + * and WS0 == true), the ping operation will only reload WCV.
> >
> > Below is the field comment about ws0_mode, it says ws0_mode is only
> > for rebooting in second stage timeout, but kexec/kdump can reboot in
> > either first or second stage
> 
> Great thanks for your feedback.
> 
> yes, if kexec/kdump reboot the system before the WS0, ws0_mode may not be set.
> in this case, if WS0 is triggered during the reboot(AFAIK, panic will
> disable irq, and in the early boot stage of system, irq is disabled,
> too.), ws0_mode will be set at the next "open" in kdump kernel
> if WS0 haven't triggered until the watchdog is opened again in kdump
> kernel , ws0_mode won't  be set.
> 
> ws0_mode doesn't indicate if the system is in the kdump kernel, it
> indicates that if WS0 is triggered, when the watchdog is initialized.
> 
> Do I answer your question?

Yes, thanks for explanation. So it sounds better to change the comment like below?
from
(reboot by kexec/kdump in panic with watchdog enabled and WS0 == true)
to
(reboot in the pre-timeout stage and WS0 == true)

Thanks
Dave
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