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

[Xingyu Chen]

Hi, Rob

On 2019/12/19 4:34, Rob Herring wrote:
> 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@xxxxxxxxxxx> wrote:
> > > > > [...]
> > > > > > +examples:
> > > > > > +Â - |
> > > > > > +ÂÂÂ watchdog {
> > > > > > +ÂÂÂÂÂÂÂÂÂ compatible = "amlogic,meson-sec-wdt";
> > > > > > +ÂÂÂÂÂÂÂÂÂ timeout-sec = <60>;
> > > > > > +ÂÂÂ };
> > > > > 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 driverïand 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'.
Thanks for your guidance.
>   
> > 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";
> >
> >  ÂÂÂ watchdog {
> >  ÂÂÂ ÂÂÂ compatible = "amlogic,meson-sec-wdt";
> >  ÂÂÂ ÂÂÂ timeout-sec = <60>;
> >  ÂÂÂ }
> > }
> >
> > 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 {
> >  ÂÂÂ compatible = "amlogic,meson-gxbb-sm";
> >
> >  ÂÂÂ watchdog {
> >  ÂÂÂÂÂÂÂ compatible = "amlogic,meson-sec-wdt";
> >  ÂÂÂÂÂÂÂ timeout-sec = <60>;
> >  ÂÂÂ }
> > }
> >
> > The method 3 looks better for me, do you have a better suggestion ? Thanks
> >
> > BR
> > > Guenter
> > >
> > > .
> .