Re: [PATCH 02/14] dt-bindings: soc: milbeaut: Add Milbeaut trampoline description

[Sugaya, Taichi]

Hi,

On 2018/11/30 17:16, Stephen Boyd wrote:
> Quoting Sugaya, Taichi (2018-11-29 04:24:51)
> > On 2018/11/28 11:01, Stephen Boyd wrote:
> > > Quoting Sugaya Taichi (2018-11-18 17:01:07)
> > > >    create mode 100644 Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt b/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
> > > > new file mode 100644
> > > > index 0000000..f5d906c
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/soc/socionext/socionext,m10v.txt
> > > > @@ -0,0 +1,12 @@
> > > > +Socionext M10V SMP trampoline driver binding
> > > > +
> > > > +This is a driver to wait for sub-cores while boot process.
> > > > +
> > > > +- compatible: should be "socionext,smp-trampoline"
> > > > +- reg: should be <0x4C000100 0x100>
> > > > +
> > > > +EXAMPLE
> > > > +       trampoline: trampoline@0x4C000100 {
> > > Drop the 0x part of unit addresses.
> >
> > Okay.
> >
> >
> > > > +               compatible = "socionext,smp-trampoline";
> > > > +               reg = <0x4C000100 0x100>;
> > > Looks like a software construct, which we wouldn't want to put into DT
> > > this way. DT doesn't describe drivers.
> > We would like to use this node only getting the address of the
> > trampoline area
> > in which sub-cores wait. (They have finished to go to this area in previous
> > bootloader process.)
>
> Is this area part of memory, or a special SRAM? If it's part of memory,
> I would expect this node to be under the reserved-memory node and
> pointed to by some other node that uses this region. Could even be the
> CPU nodes.

Yes, 0x4C000100 is a part of memory under the reserved-memory node. So 
we would like to use the SRAM ( allocated 0x00000000 ) area instead.
BTW, sorry, the trampoline address of this example is simply wrong.  We 
were going to use a part of the SRAM from the beginning.

> > So should we embed the constant value in source codes instead of getting
> > from
> > DT because the address is constant at the moment? Or is there other
> > approach?
>
> If it's constant then that also works. Why does it need to come from DT
> at all then?

We think it is not good to embed constant value in driver codes and do 
not have another way...
Are there better ways?

Thanks
Sugaya Taichi

>