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From:   Rob Herring <robh@kernel.org>
Date:   Mon, 11 Mar 2019 16:26:16 -0500
Message-ID: <CAL_JsqJiKx8UvZ8qu-YaaPooLbSMKANSX=YZQO=Nm_anD2v9gw@mail.gmail.com>
Subject: Re: [PATCH RESEND V2 1/4] dt-bindings: fsl: scu: add watchdog binding
To:     Aisheng Dong <aisheng.dong@nxp.com>
Cc:     Anson Huang <anson.huang@nxp.com>,
        Guenter Roeck <linux@roeck-us.net>,
        "mark.rutland@arm.com" <mark.rutland@arm.com>,
        "ulf.hansson@linaro.org" <ulf.hansson@linaro.org>,
        "heiko@sntech.de" <heiko@sntech.de>,
        "catalin.marinas@arm.com" <catalin.marinas@arm.com>,
        "will.deacon@arm.com" <will.deacon@arm.com>,
        "bjorn.andersson@linaro.org" <bjorn.andersson@linaro.org>,
        "festevam@gmail.com" <festevam@gmail.com>,
        "jagan@amarulasolutions.com" <jagan@amarulasolutions.com>,
        Andy Gross <andy.gross@linaro.org>,
        dl-linux-imx <linux-imx@nxp.com>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-watchdog@vger.kernel.org" <linux-watchdog@vger.kernel.org>,
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        Jens Wiklander <jens.wiklander@linaro.org>
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+Jens W

On Thu, Mar 7, 2019 at 6:22 AM Aisheng Dong <aisheng.dong@nxp.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