linux-kernel - Re: [PATCH 1/2] dt-bindings: watchdog: Add arm,smc-wdt watchdog arm,smc-wdt compatible

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Date:   Wed, 19 Feb 2020 15:04:54 -0800
From:   Julius Werner <jwerner@...omium.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Evan Benn <evanbenn@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Julius Werner <jwerner@...omium.org>,
        devicetree@...r.kernel.org, Guenter Roeck <linux@...ck-us.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-watchdog@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: watchdog: Add arm,smc-wdt watchdog
 arm,smc-wdt compatible

> You are not the first 'watchdog in firmware accessed via an SMC call'.
> Is there some more detail about what implementation this is? Part of
> TF-A? Defined by some spec (I can dream)?

This is just some random implementation written by me because we
needed one. I would like it to be the new generic implementation, but
it sounds like people here prefer the naming to be MediaTek specific
(at least for now). The other SMC watchdog we're aware of is
imx_sc_wdt but unfortunately that seems to hardcode platform-specific
details in the interface (at least in the pretimeout SMC) so we can't
just expand that. With this driver I tried to directly wrap the kernel
watchdog interface so it should be platform-agnostic and possible to
expand this driver to other platforms later if desired. The SMC
function ID would still always have to be platform-specific,
unfortunately (but we could pass it in through the device tree), since
the Arm SMC spec doesn't really leave any room for OS-generic SMCs
like this.