linux-kernel - Re: [PATCH 0/2] Add support for Gunyah Watchdog

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Message-ID: <99cacf08-0fb4-4b44-9036-96ea5fe01c10@quicinc.com>
Date: Fri, 5 Sep 2025 05:30:52 +0530
From: Pavan Kondeti <pavan.kondeti@....qualcomm.com>
To: Rob Herring <robh@...nel.org>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Hrishabh Rajput <hrishabh.rajput@....qualcomm.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-watchdog@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/2] Add support for Gunyah Watchdog

On Thu, Sep 04, 2025 at 05:51:24PM -0500, Rob Herring wrote:
> > >
> > > Why can't you probe by trying to see if watchdog smc call succeeds to
> > > see if there is a watchdog? Then you don't need DT for it.
> >
> > There apparently isn't a good way to tell from a running system whether
> > Gunyah is present, unless you make a smc call (which could in theory be
> > parsed by something else, say a different hypervisor..), but then this
> > patch only introduces the watchdog interface, without all the cruft that
> > would actually let us identify the hypervisor, get its version ID and
> > perform sanity checks..
> 
> IIRC, last time we got just a gunyah node. Now it's that plus a
> watchdog. What's next? I'm not really a fan of $soc_vendor hypervisor
> interfaces. I doubt anyone else is either. We have all sorts of
> standard interfaces already between virtio, vfio, EFI, SCMI, PSCI,
> etc. Can we please not abuse DT with $soc_vendor hypervisor devices.
> 

We are trying to make the watchdog work with existing SoCs, so we are
sticking with the existing interfaces. The newer devices will not
necessarily need DT to probe hypervisor interfaces.

To answer your question on why can't you probe watchdog smc call to see
if there is a watchdog. Yes, we can do that. It is just that we won't be
able to support pre-timeout IRQ. This IRQ is optional for watchdog
functionality, so this is something we can explore.

Thanks for the feedbck.

Thanks,
Pavan