[PATCH/RFC 06/11] ARM: shmobile: r8a7790: Link CPG to RST using "renesas, modemr"

[Geert Uytterhoeven]

Hi Laurent,

On Tue, Jul 7, 2015 at 6:20 PM, Laurent Pinchart
<laurent.pinchart at ideasonboard.com> wrote:
>> >> --- a/arch/arm/boot/dts/r8a7790.dtsi
>> >> +++ b/arch/arm/boot/dts/r8a7790.dtsi
>> >> @@ -1115,6 +1115,7 @@
>> >>                                            "lb", "qspi", "sdh", "sd0",
>> >>                                            "sd1",
>> >>                                            "z", "rcan", "adsp";
>> >>                       #power-domain-cells = <0>;
>> >> +                     renesas,modemr = <&rst 0x60>;
>> >
>> > I have mixed feelings about this as I don't think it really describes the
>> > hardware.
>>
>> From the R-Car Gen2 manual:
>>
>> 8. Reset (RST)
>> 8.1 Features
>> The following functions are implemented by RST.
>> [...]
>> Latching of the levels on mode pins when PRESET# is negated
>> Mode monitoring register
>>
>> 7. Clock Pulse Generator (CPG)
>> 7.2 Input/Output Pins
>> Table 7.1 lists the CPG pin configuration.
>> Table 7.1 Pin Configuration and Functions of CPG
>> Pin Name Function I/O Description
>> [...]
>> MD0 Mode 0 ...
>>
>> Hence there definitely is a link between the (latched) values in the RST
>> module and CPG configuration. This link is expressed using the
>> "renesas,modemr" property, where the phandle provides the link to the RST
>> block, and the register offset provides a way for software to read the
>> configuration.
>
> The mode bits of course influence the CPG (otherwise we wouldn't be having
> this discussion :-)), but to me it looks more like a configuration broadcast
> through the whole SoC than a real link between two IP cores. It's obviously
> subject to interpretation.

Yep.

Broadcast? Like a bus clock? For that we also have properties with phandles...

Syscon is the Hot New Abstraction for a module that provides a bunch of
registers needed by drivers for other modules. Those other modules need
some way to refer to the appropriate syscon register.

The RST module definitely falls in that category: CPG needs the MODEMR
register, watchdog (RWDT/SWDT) needs the Watchdog Timer Reset Control Register,
and APMU probably needs the CA15/7 reset control registers.

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