linux-kernel - Re: [PATCH RESEND V2 1/4] dt-bindings: fsl: scu: add watchdog binding

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Message-ID: <CAL_JsqJiKx8UvZ8qu-YaaPooLbSMKANSX=YZQO=Nm_anD2v9gw@mail.gmail.com>
Date:   Mon, 11 Mar 2019 16:26:16 -0500
From:   Rob Herring <robh@...nel.org>
To:     Aisheng Dong <aisheng.dong@....com>
Cc:     Anson Huang <anson.huang@....com>,
        Guenter Roeck <linux@...ck-us.net>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "ulf.hansson@...aro.org" <ulf.hansson@...aro.org>,
        "heiko@...ech.de" <heiko@...ech.de>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "festevam@...il.com" <festevam@...il.com>,
        "jagan@...rulasolutions.com" <jagan@...rulasolutions.com>,
        Andy Gross <andy.gross@...aro.org>,
        dl-linux-imx <linux-imx@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        "arnd@...db.de" <arnd@...db.de>,
        "marc.w.gonzalez@...e.fr" <marc.w.gonzalez@...e.fr>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "enric.balletbo@...labora.com" <enric.balletbo@...labora.com>,
        "horms+renesas@...ge.net.au" <horms+renesas@...ge.net.au>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        Daniel Baluta <daniel.baluta@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "olof@...om.net" <olof@...om.net>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Jens Wiklander <jens.wiklander@...aro.org>
Subject: Re: [PATCH RESEND V2 1/4] dt-bindings: fsl: scu: add watchdog binding

+Jens W

On Thu, Mar 7, 2019 at 6:22 AM Aisheng Dong <aisheng.dong@....com> wrote:
>
> Hi Rob,
>
> > > > I think Rob suggested that the SCU parent driver should instantiate
> > > > the watchdog without explicit watchdog node. That would be possible,
> > > > but it currently uses
> > > > devm_of_platform_populate() to do the instantiation, and changing
> > > > that would be a mess. Besides, it does sem to me that your suggested
> > > > node would describe the hardware, so I am not sure I understand the
> > reasoning.
> >
> > It would just be a call to create a platform device instead. How is that a mess?
> >
> > It's describing firmware. We have DT for describing h/w we've failed to make
> > discoverable. We should not repeat that and just describe firmware in DT.
> > Make the firmware discoverable! Though there are cases like firmware
> > provided clocks where we still need something in DT, but this is not one of
> > them.
> >
>
> The watchdog node here in question actually is not using SCU firmware call.
> Due to security requirement by SCU, watchdog can only be accessed in
> security mode, for IMX case, via ARM Trust Firmware. That means the
> watchdog used in Linux actually is using ARM SMC call and does not
> depend SCU driver. So It would be strange for SCU driver to instantiate it.
>
> For this situation, do you think we can move watchdog out of scu node?
> Maybe rename the compatible string like "fsl,imx8qxp-sip-watchdog"
> because it's actually a watchdog serviced by ATF firmware.

Yes, but that creates more questions. What exactly does ATF talk to
for the watchdog? The SCU firmware?

Maybe ATF should define and provide a standard watchdog interface? It
is still a question of making the firmware discoverable rather than
trying to describe the firmware in DT.

Rob