Re: [PATCH v3 04/17] dt-bindings: soc: mobileye: add EyeQ5 OLB system controller

[Andrew Davis]

On 1/25/24 5:01 AM, Théo Lebrun wrote:
> Hello,
>
> On Thu Jan 25, 2024 at 8:51 AM CET, Krzysztof Kozlowski wrote:
> > On 24/01/2024 16:14, Rob Herring wrote:
> > > > +
> > > > +      pinctrl-b {
> > > > +        compatible = "mobileye,eyeq5-b-pinctrl";
> > > > +        #pinctrl-cells = <1>;
> > > > +      };
> > > > +    };
> > >
> > > This can all be simplified to:
> > >
> > > system-controller@e00000 {
> > >      compatible = "mobileye,eyeq5-olb", "syscon";
> > >      reg = <0xe00000 0x400>;
> > >      #reset-cells = <2>;
> > >      #clock-cells = <1>;
> > >      clocks = <&xtal>;
> > >      clock-names = "ref";
> > >
> > >      pins { ... };
> > > };
> > >
> > > There is no need for sub nodes unless you have reusable blocks or each
> > > block has its own resources in DT.
> >
> > Yes, however I believe there should be resources here: each subnode
> > should get its address space. This is a bit tied to implementation,
> > which currently assumes "everyone can fiddle with everything" in this block.
> >
> > Theo, can you draw memory map?
>
> It would be a mess. I've counted things up. The first 147 registers are
> used in this 0x400 block. There are 31 individual blocks, with 7
> registers unused (holes to align next block).
>
> Functions are reset, clocks, LBIST, MBIST, DDR control, GPIO,
> accelerator control, CPU entrypoint, PDTrace, IRQs, chip info & ID
> stuff, control registers for PCIe / eMMC / Eth / SGMII / DMA / etc.
>
> Some will never get used from Linux, others might. Maybe a moderate
> approach would be to create ressources for major blocks and make it
> evolve organically, without imposing that all uses lead to a new
> ressource creation.

That is usually how nodes are added to DT. If you modeled this
system-controller space as a "simple-bus" instead of a "syscon"
device, you could add nodes as you implement them. Rather than
all at once as you have to by treating this space as one large
blob device.

Andrew

> Thanks,
>
> --
> Théo Lebrun, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com