Hi Laurent,

On Tue, Jul 7, 2015 at 6:20 PM, Laurent Pinchart
[off-list ref] wrote:

quoted

quoted

quoted

--- 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