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

[Lurndal, Scott]

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