dt-bindings: serial: renesas,rsci: Add optional secondary clock input

Update the RSCI binding to support an optional secondary clock input on
the RZ/T2H SoC. At boot, the RSCI operates using the default synchronous
clock (PCLKM core clock), which is enabled by the bootloader. However, to
support a wider range of baud rates, the hardware also requires an
asynchronous external clock input. Clock selection is controlled
internally by the CCR3 register in the RSCI block.

Due to an incomplete understanding of the hardware, the original binding
defined only a single clock ("fck"), which is insufficient to describe the
full capabilities of the RSCI on RZ/T2H. This update corrects the binding
by allowing up to three clocks and defining the `clock-names` as
"operation", "bus", and optionally "sck" for the asynchronous clock input.

This is an ABI change, as it modifies the expected number and names of
clocks. However, since there are no in-kernel consumers of this binding
yet, the change is considered safe and non-disruptive.

Also remove the unneeded `serial0` alias from the DTS example and use
the R9A09G077_CLK_PCLKM macro for core clock.

Signed-off-by: Thierry Bultel <[email protected]>
Signed-off-by: Lad Prabhakar <[email protected]>
Reviewed-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: "Rob Herring (Arm)" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: Thierry Bultel

Documentation/devicetree/bindings/serial/renesas,rsci.yaml

@@ -41,10 +41,15 @@ properties:
       - const: tei
 
   clocks:
-    maxItems: 1
+    minItems: 2
+    maxItems: 3
 
   clock-names:
-    const: fck # UART functional clock
+    minItems: 2
+    items:
+      - const: operation
+      - const: bus
+      - const: sck # optional external clock input
 
   power-domains:
     maxItems: 1
@@ -66,10 +71,6 @@ examples:
     #include <dt-bindings/interrupt-controller/arm-gic.h>
     #include <dt-bindings/clock/renesas-cpg-mssr.h>
 
-    aliases {
-        serial0 = &sci0;
-    };
-
     sci0: serial@80005000 {
         compatible = "renesas,r9a09g077-rsci";
         reg = <0x80005000 0x400>;
@@ -78,7 +79,7 @@ examples:
                      <GIC_SPI 592 IRQ_TYPE_EDGE_RISING>,
                      <GIC_SPI 593 IRQ_TYPE_LEVEL_HIGH>;
         interrupt-names = "eri", "rxi", "txi", "tei";
-        clocks = <&cpg CPG_MOD 108>;
-        clock-names = "fck";
+        clocks = <&cpg CPG_MOD 8>, <&cpg CPG_CORE 13>;
+        clock-names = "operation", "bus";
         power-domains = <&cpg>;
     };