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

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Message-ID: <20170321124813.GB31496@slurndal-lnx1.caveonetworks.com>
Date:   Tue, 21 Mar 2017 05:48:13 -0700
From:   "Lurndal, Scott" <Scott.Lurndal@...ium.com>
To:     Fu Wei <fu.wei@...aro.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Linaro ACPI Mailman List <linaro-acpi@...ts.linaro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Wim Van Sebroeck <wim@...ana.be>, Wei Huang <wei@...hat.com>,
        Tomasz Nowicki <tn@...ihalf.com>,
        Timur Tabi <timur@...eaurora.org>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Len Brown <lenb@...nel.org>,
        "Abdulhamid, Harb" <harba@...eaurora.org>,
        Julien Grall <julien.grall@....com>,
        linux-watchdog@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Marc Zyngier <marc.zyngier@....com>,
        Jon Masters <jcm@...hat.com>,
        Christopher Covington <cov@...eaurora.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Christoffer Dall <christoffer.dall@...aro.org>
Subject: Re: [Linaro-acpi] [PATCH v21 13/13] acpi/arm64: Add SBSA Generic
 Watchdog support in GTDT driver

On Tue, Mar 21, 2017 at 11:48:02AM +0800, Fu Wei wrote:
> Hi Mark, Lurndal,
> 
> >>       The base server system implements _a_ Generic Watchdog as
> >>       specified in APPENDIX A: Generic Watchdog.
> >
> >   It is a requirement of a conforming implementation that there
> > be a generic watchdog (impl as per the appendix).   That doesn't preclude
> > an implmentation from providing additional watchdogs (for example, if
> > the processor implements EL3, it is likely that an implementation
> > will include a secure watchdog as well as a non-secure watchdog).
> >
> >   The SBSA describes the minimal hardware requirements for a
> > compliant server.
> 
> So I think, for the SBSA watchdog:
> 
> (1) there maybe more then one non-secure watchdog in GTDT

I suppose a firmware vendor could chose to expose more than the
platform minimum to linux.   Not quite sure what linux would
do with it :-)

> 
> (2) we may also need to skip  secure watchdogs in GTDT,
> and only register non-secure watchdogs into platform resources.

The secure watchdog will, be definition, never be accessible
to non-secure EL2 or non-secure EL1, so only in the case of
a secure EL1 operating system would the secure watchdog ever
be conveyed through ACPI.   I don't think secure EL1 is in
the scope of the SBSA, or something that needs to be accomodated
in the GTDT at this time.

scott