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

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Date:   Thu, 7 Mar 2019 12:22:32 +0000
From:   Aisheng Dong <aisheng.dong@....com>
To:     Rob Herring <robh@...nel.org>, Anson Huang <anson.huang@....com>
CC:     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>
Subject: RE: [PATCH RESEND V2 1/4] dt-bindings: fsl: scu: add watchdog binding

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.

Regards
Dong Aisheng