clk: shmobile: r8a7778: Add CPG/MSTP Clock Domain support

Add Clock Domain support to the R-Car M1A Clock Pulse Generator (CPG)
driver using the generic PM Domain. This allows to power-manage the
module clocks of SoC devices that are part of the CPG/MSTP Clock Domain
using Runtime PM, or for system suspend/resume.

SoC devices that are part of the CPG/MSTP Clock Domain and can be
power-managed through an MSTP clock should be tagged in DT with a proper
"power-domains" property.

Signed-off-by: Geert Uytterhoeven <[e-mail]>
Acked-by: Stephen Boyd <[e-mail]>
Reviewed-by: Ulf Hansson <[e-mail]>
Signed-off-by: Simon Horman <[e-mail]>

Documentation/devicetree/bindings/clock/renesas,r8a7778-cpg-clocks.txt

···
 * Renesas R8A7778 Clock Pulse Generator (CPG)
 
 The CPG generates core clocks for the R8A7778. It includes two PLLs and
-several fixed ratio dividers
+several fixed ratio dividers.
+The CPG also provides a Clock Domain for SoC devices, in combination with the
+CPG Module Stop (MSTP) Clocks.
 
 Required Properties:
 
···
   - #clock-cells: Must be 1
   - clock-output-names: The names of the clocks. Supported clocks are
     "plla", "pllb", "b", "out", "p", "s", and "s1".
+  - #power-domain-cells: Must be 0
+
+SoC devices that are part of the CPG/MSTP Clock Domain and can be power-managed
+through an MSTP clock should refer to the CPG device node in their
+"power-domains" property, as documented by the generic PM domain bindings in
+Documentation/devicetree/bindings/power/power_domain.txt.
 
 
-Example
--------
+Examples
+--------
+
+  - CPG device node:
 
 	cpg_clocks: cpg_clocks@ffc80000 {
 		compatible = "renesas,r8a7778-cpg-clocks";
···
 		clocks = <&extal_clk>;
 		clock-output-names = "plla", "pllb", "b",
 				     "out", "p", "s", "s1";
+		#power-domain-cells = <0>;
+	};
+
+
+  - CPG/MSTP Clock Domain member device node:
+
+	sdhi0: sd@ffe4c000 {
+		compatible = "renesas,sdhi-r8a7778";
+		reg = <0xffe4c000 0x100>;
+		interrupts = <0 87 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&mstp3_clks R8A7778_CLK_SDHI0>;
+		power-domains = <&cpg_clocks>;
+		status = "disabled";
 	};

arch/arm/mach-shmobile/Kconfig

···
 
 config PM_RCAR
 	bool
+	select PM_GENERIC_DOMAINS if PM
 
 config PM_RMOBILE
 	bool

drivers/clk/shmobile/clk-r8a7778.c

···
 	}
 
 	of_clk_add_provider(np, of_clk_src_onecell_get, &cpg->data);
+
+	cpg_mstp_add_clk_domain(np);
 }
 
 CLK_OF_DECLARE(r8a7778_cpg_clks, "renesas,r8a7778-cpg-clocks",