linux-kernel - Re: [PATCH v5 2/4] dt-bindings: watchdog: add new binding for meson secure watchdog

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Date:   Wed, 18 Dec 2019 14:34:04 -0600
From:   Rob Herring <robh@...nel.org>
To:     Xingyu Chen <xingyu.chen@...ogic.com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Qianggui Song <qianggui.song@...ogic.com>,
        devicetree@...r.kernel.org, linux-watchdog@...r.kernel.org,
        Jianxin Pan <jianxin.pan@...ogic.com>,
        linux-kernel@...r.kernel.org, Jian Hu <jian.hu@...ogic.com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        Jerome Brunet <jbrunet@...libre.com>
Subject: Re: [PATCH v5 2/4] dt-bindings: watchdog: add new binding for meson
 secure watchdog

On Wed, Dec 18, 2019 at 03:37:49PM +0800, Xingyu Chen wrote:
> Hi, Guenter Martin
> 
> On 2019/12/16 21:30, Guenter Roeck wrote:
> > On 12/15/19 10:03 PM, Xingyu Chen wrote:
> > > Hi, Martin
> > > 
> > > Sorry for the late reply.
> > > 
> > > On 2019/12/13 4:05, Martin Blumenstingl wrote:
> > > > Hi Xingyu and Rob,
> > > > 
> > > > On Thu, Dec 12, 2019 at 1:20 PM Xingyu Chen
> > > > <xingyu.chen@...ogic.com> wrote:
> > > > [...]
> > > > > +examples:
> > > > > +  - |
> > > > > +    watchdog {
> > > > > +          compatible = "amlogic,meson-sec-wdt";
> > > > > +          timeout-sec = <60>;
> > > > > +    };
> > > > in v3 of this patch Rob commented that there shouldn't be an OF node
> > > > if there are no additional properties
> > > > with timeout-sec there's now an additional property so my
> > > > understanding is that it's fine to have an OF node
> > > Your understanding is correct.
> > > > 
> > > > what I don't understand yet is where this node should be placed.
> > > > is it supposed to be a child node of the secure monitor node (for
> > > > which we already have a binding here:
> > > > Documentation/devicetree/bindings/firmware/meson/meson_sm.txt) or
> > > > where else would we place it inside the .dts?
> > > IMO,  Although the watchdog node need to reference the meson_sm
> > > node, there is no
> > > bus-like dependencies between the devices which the two nodes
> > > corresponding to.
> > > so i think that the watchdog node as child node of meson_sm maybe
> > > not appropriate.
> > 
> > The watchdog driver needs the meson SM's dt node, and it depends on the
> > existence
> > of that node. That seems enough of a relationship to warrant having it
> > as child note.
> Thanks for your reply, if i take the wdt node as child of secure monitor
> (sm), how should
> i register or find the wdt device ?
> 
> I only think of the following three methods :
> 1). update the sm driver，and scan&register wdt device when the sm driver
> probes(It is like i2c), but there
> are too many changes involved.

Just add of_platform_default_populate() call and clean-up calls. That's 
not what I'd call 'too many changes'.

 
> 2). add "simple-bus" key string to compatible of sm node, and it will make
> the child node is registered as
> platform device, but it seems that the key string is not match current
> scene.

You previously said it's not a bus...

> 
> secure-monitor {
>     compatible = "amlogic,meson-gxbb-sm",  "simple-bus";
> 
>     watchdog {
>         compatible = "amlogic,meson-sec-wdt";
>         timeout-sec = <60>;
>     }
> }
> 
> 3).  don't register device, and find directly the watchdog node by using the
> of_* API in watchdog
> driver (Eg: linux-4.x/drivers/tee/optee/core.c)
> 
> secure-monitor {
>     compatible = "amlogic,meson-gxbb-sm";
> 
>     watchdog {
>         compatible = "amlogic,meson-sec-wdt";
>         timeout-sec = <60>;
>     }
> }
> 
> The method 3 looks better for me, do you have a better suggestion ? Thanks
> 
> BR
> > 
> > Guenter
> > 
> > .
> >