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

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Message-ID: <CADyBb7vxbdftskfDKSmgz82=Y2XtCYOawp2mGiUsJ7f=H1ZAoA@mail.gmail.com>
Date:	Tue, 13 Oct 2015 16:34:25 +0800
From:	Fu Wei <fu.wei@...aro.org>
To:	Dave Young <dyoung@...hat.com>
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

Hi Dave,

On 16 September 2015 at 09:57, Dave Young <dyoung@...hat.com> wrote:
>> >> 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)

" in the pre-timeout stage" means " WS0 == true", so I think we should say:
(reboot with watchdog enabled and WS0 == true)

Thanks for your suggestion.

>
> Thanks
> Dave



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat Software (Beijing) Co.,Ltd.Shanghai Branch
Ph: +86 21 61221326(direct)
Ph: +86 186 2020 4684 (mobile)
Room 1512, Regus One Corporate Avenue,Level 15,
One Corporate Avenue,222 Hubin Road,Huangpu District,
Shanghai,China 200021
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