linux-kernel - Re: [PATCH v4 5/7] Watchdog: introduce ARM SBSA watchdog driver

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Date:	Thu, 10 Sep 2015 18:45:17 -0400
From:	Jon Masters <jcm@...hat.com>
To:	Timur Tabi <timur@...eaurora.org>,
	Guenter Roeck <linux@...ck-us.net>
CC:	fu.wei@...aro.org, Suravee.Suthikulpanit@....com,
	linaro-acpi@...ts.linaro.org, linux-watchdog@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, tekkamanninja@...il.com,
	graeme.gregory@...aro.org, al.stone@...aro.org,
	hanjun.guo@...aro.org, ashwin.chaugule@...aro.org, arnd@...db.de,
	vgandhi@...eaurora.org, wim@...ana.be, leo.duran@....com,
	corbet@....net, mark.rutland@....com, catalin.marinas@....com,
	will.deacon@....com, rjw@...ysocki.net
Subject: Re: [PATCH v4 5/7] Watchdog: introduce ARM SBSA watchdog driver

On 06/03/2015 02:53 PM, Timur Tabi wrote:
> On 06/03/2015 01:25 PM, Guenter Roeck wrote:
>> In general the idea here would be to use a crashdump kernel, which,
>> when loaded, would reset the watchdog before it fires. This kernel
>> would then write a core dump to a specified location.
> 
> What is the mechanism for resetting the watchdog?  The only code that 
> knows about the hardware registers is this driver.  Does the crashdump 
> kernel call the watchdog stop function?
> 
>> If arm64 doesn't support a crashdump kernel, it might still be possible
>> to log the backtrace somewhere (eg in nvram using pstore if that is
>> supported via acpi or efi).

Just to go back and explicitly answer this, arm64 does have support for
crashdump, using the standard kexec/kdump approach, exactly as on x86.
There's still some more work to be done to get the ACPI case fully
upstream (e.g. on X-Gene platforms such as the HP ProLiant Moonshot m400
we need non-PSCI CPU parking protocol offlining when booting in
UEFI/ACPI mode), but it's what we are doing in RHEL(SA) and the goal is
to help clean up the remaining pieces upstream there.

Jon.

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