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

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Message-ID: <20200219232005.GA9737@roeck-us.net>
Date:   Wed, 19 Feb 2020 15:20:05 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Julius Werner <jwerner@...omium.org>
Cc:     Rob Herring <robh@...nel.org>, Evan Benn <evanbenn@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>, devicetree@...r.kernel.org,
        "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

On Wed, Feb 19, 2020 at 03:04:54PM -0800, Julius Werner wrote:
> > 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

There is one more pending, for Meson SMC.

https://patchwork.kernel.org/project/linux-watchdog/list/?series=227733

Unfortunately it uses Meson firmware API functions, though it has pretty
much the same functionality since those ultimately end up calling
arm_smccc_smc().

Guenter

> 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.