[PATCH/RFC v2 01/11] PM / Domains: Add DT bindings for the R-Car System Controller

[Geert Uytterhoeven]

Hi Rob,

On Thu, Feb 18, 2016 at 3:38 PM, Rob Herring <robh at kernel.org> wrote:
> On Mon, Feb 15, 2016 at 10:16:50PM +0100, Geert Uytterhoeven wrote:
>> The Renesas R-Car System Controller provides power management for the
>> CPU cores and various coprocessors, following the generic PM domain
>> bindings in Documentation/devicetree/bindings/power/power_domain.txt.
>>
>> This supports R-Car Gen1, Gen2, and Gen3.
>>
>> Signed-off-by: Geert Uytterhoeven <geert+renesas at glider.be>
>> ---
>> Alternatives I considered:
>>
>>   - Using a single node per power register block, even if it contains
>>     multiple domains, e.g.:
>>
>>           pd_ca15_scu: ca15_scu at 180 {
>>                   reg = <0x180 0x20>;
>>                   #address-cells = <1>;
>>                   #size-cells = <0>;
>>                   #power-domain-cells = <0>;
>>                   renesas,interrupt-bits = <12>;
>>
>>                   pd_ca15_cpu: ca15_cpu at 40 {
>>                           reg = <0x40 0x20>;
>>                           #power-domain-cells = <1>;
>>                           renesas,pm-domain-indices = <0 1>;
>>                           renesas,pm-domain-names =
>>                                   "ca15_cpu0", "ca15_cpu1";
>>                           renesas,interrupt-bits = <0 1>;
>>                   };
>>           };
>>
>>     Notes:
>>       - You cannot just have a property with the number of domains, as
>>       index 0 is not used on R-Car H1. Hence the need for
>>       "renesas,pm-domain-indices" and "renesas,interrupt-bits",
>>       - "#power-domain-cells = <1>" for nodes with multiple domains,
>>       which allows typos in "power-domains = <&pd_ca15_cpu n>", using
>>       an invalid value of "n".
>>
>>   - Using a linear description in DT:
>>       - Needs parent links for subdomains,
>>       - More complicated to parse (lesson learned from R-Mobile PM
>>       Domain support).
>>
>>   - Keeping the power register block offset and the bit number as separate
>>     "reg" cells, increasing "#address-cells" from 2 to 3,
>>
>>   - Merging the interrupt bit (which needs only 5 bits) in the other "reg"
>>     cell, decreasing "#address-cells" from 2 to 1.
>
> I think I'd move to not encoding mulitple things into reg. This seems
> like a bit of abuse of reg. Otherwise, I don't have much to comment on.

Thanks!

(quoting the encoding of the reg properties)
> +== PM Domain Nodes ==
> +
> +Each of the PM domain nodes represents a PM domain, as documented by the
> +generic PM domain bindings in
> +Documentation/devicetree/bindings/power/power_domain.txt.
> +
> +Required properties:
> +  - #power-domain-cells: Must be 0.
> +  - reg: This property must contain 2 values:
> +          - The first value is the number of the interrupt bit representing
> +            the power area in the various Interrupt Registers (e.g. SYSCISR,
> +            Interrupt Status Register),
> +          - The second value encodes the power register block offset (which is
> +            a multiple of 64), and the number of the bit representing the
> +            power area in the various Power Control Registers (e.g. PWROFFSR,
> +            Power Shutoff Status Register). This value is created by ORing
> +            these two numbers.

Not encoding multiple things into reg means adding more properties to provide
that information, iff we want to describe the PM Domain Nodes in DT.
I considered the reg property a two-dimensional address space.

Taking the lessons from CCF and the new CPG/MSSR bindings into account
(which was BTW designed after the SYSC DT bindings), perhaps the PM Domain
hierarchy should be moved from DT to C, in the driver, too?

That would mean we have in DT:
  1) "#power-domain-cells = <1>"
  2) defines for the various domains, e.g. "#define R8A7791_PD_CA15_SCU      12"
  3) e.g. "power-domains = <&sysc R8A7791_PD_CA15_SCU>"
  4) and we can get rid of the fallback compatibility strings again.

Thoughts?

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds