linux-kernel - Re: [PATCH v21 13/13] acpi/arm64: Add SBSA Generic Watchdog support in GTDT driver

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Message-ID: <20170320180949.GM31213@leverpostej>
Date:   Mon, 20 Mar 2017 18:09:50 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Fu Wei <fu.wei@...aro.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        linux-arm-kernel@...ts.infradead.org,
        Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        rruigrok@...eaurora.org, "Abdulhamid, Harb" <harba@...eaurora.org>,
        Christopher Covington <cov@...eaurora.org>,
        Timur Tabi <timur@...eaurora.org>,
        G Gregory <graeme.gregory@...aro.org>,
        Al Stone <al.stone@...aro.org>, Jon Masters <jcm@...hat.com>,
        Wei Huang <wei@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        Leo Duran <leo.duran@....com>,
        Wim Van Sebroeck <wim@...ana.be>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-watchdog@...r.kernel.org, Tomasz Nowicki <tn@...ihalf.com>,
        Christoffer Dall <christoffer.dall@...aro.org>,
        Julien Grall <julien.grall@....com>
Subject: Re: [PATCH v21 13/13] acpi/arm64: Add SBSA Generic Watchdog support
 in GTDT driver

On Tue, Mar 21, 2017 at 01:57:58AM +0800, Fu Wei wrote:
> On 18 March 2017 at 04:01, Mark Rutland <mark.rutland@....com> wrote:
> > On Tue, Feb 07, 2017 at 02:50:15AM +0800, fu.wei@...aro.org wrote:

> > I've not been able to find where the ACPI spec says that zero is not a
> > valid GSIV. This may simply be an oversight/ambiguity in the spec.
> >
> > Is there any statement to that effect?
> 
> you are right, zero is a  valid GSIV, I will delete this check. Thanks

That being the case, how does one describe a watchdog that does not have
an interrupt?

As I mentioned, I think this is an oversight/ambiguity in the spec tat
we should address.

> > My reading of SBSA is that there is one watchdog in the system.
> >
> > Is that not the case?
> 
> do you mean:
> ---------------
> 4.2.4 Watchdogs
> The base server system implements a Generic Watchdog as specified in
> APPENDIX A: Generic Watchdog.
> ---------------
> 
> I am not sure about that if this is saying "we only have one SBSA
> watchdog in a system"
> 
> would you let me know where mention it? Do I miss something?

My reading was that the 'a' above meant a single element. i.e.

	The base server system implements _a_ Generic Watchdog as
	specified in APPENDIX A: Generic Watchdog.

Subsequently in 4.2.5, it is stated:

	In this scenario, the system wakeup timer or generic watchdog is
	still required to send its interrupt.

... which only makes sense if there is a single watchdog in the system.

Perhaps this is an oversight in the specification.

Thanks,
Mark.