R-Car USB 2.0 controller can change the clock source from an oscillator
to an external clock via a register. So, this patch adds support
the clock source selector as a clock driver.

Signed-off-by: Yoshihiro Shimoda <redacted>
---
 This patch is based on the renesas-drivers.git /
renesas-drivers-2017-06-27-v4.12-rc7 tag.

 Changes from v1:
  - Change this driver as a clock driver from a generic phy driver.
    https://patchwork.kernel.org/patch/9788697/
  - Remove "RFC" tag.

 .../bindings/clock/renesas,rcar-usb2-clock-sel.txt |  54 ++++++
 drivers/clk/renesas/Kconfig                        |   5 +
 drivers/clk/renesas/Makefile                       |   1 +
 drivers/clk/renesas/rcar-usb2-clock-sel.c          | 205 +++++++++++++++++++++
 4 files changed, 265 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/clock/renesas,rcar-usb2-clock-sel.txt
 create mode 100644 drivers/clk/renesas/rcar-usb2-clock-sel.c

diff --git a/Documentation/devicetree/bindings/clock/renesas,rcar-usb2-clock-sel.txt b/Documentation/devicetree/bindings/clock/renesas,rcar-usb2-clock-sel.txt
new file mode 100644
index 0000000..75ccafc
--- /dev/null
+++ b/Documentation/devicetree/bindings/clock/renesas,rcar-usb2-clock-sel.txt

@@ -0,0 +1,54 @@
+* Renesas R-Car USB 2.0 clock selector
+
+This file provides information on what the device node for the R-Car USB 2.0
+clock selector.
+
+If you connect an external clock to the USB_EXTAL pin only, you should set
+the clock rate to "usb_extal" node only.
+If you connect an oscillator to both the USB_XTAL and USB_EXTAL, this module
+is not needed because this is default setting. (Of course, you can set the
+clock rates to both "usb_extal" and "usb_xtal" nodes.
+
+Case 1: An external clock connects to R-Car SoC
+        +----------+   +--- R-Car ---------------------+
+        |External  |---|USB_EXTAL ---> all usb channels|
+        |clock     |   |USB_XTAL                       |
+        +----------+   +-------------------------------+
+In this case, we need this driver with "usb_extal" clock.
+
+Case 2: An oscillator connects to R-Car SoC
+        +----------+   +--- R-Car ---------------------+
+        |Oscillator|---|USB_EXTAL -+-> all usb channels|
+        |          |---|USB_XTAL --+                   |
+        +----------+   +-------------------------------+
+In this case, we don't need this selector.
+
+Required properties:
+- compatible: "renesas,r8a7795-rcar-usb2-clock-sel" if the device is a part of
+	      an R8A7795 SoC.
+              "renesas,r8a7796-rcar-usb2-clock-sel" if the device if a part of
+	      an R8A7796 SoC.
+              "renesas,rcar-gen3-usb2-clock-sel" for a generic R-Car Gen3
+              compatible device.
+
+              When compatible with the generic version, nodes must list the
+              SoC-specific version corresponding to the platform first
+              followed by the generic version.
+
+- reg: offset and length of the USB 2.0 clock selector register block.
+- clocks: A list of phandles and specifier pairs.
+- clock-names: Name of the clocks.
+ - The functional clock must be "ehci_ohci"
+ - The USB_EXTAL clock pin must be "usb_extal"
+ - The USB_XTAL clock pin must be "usb_xtal"
+- #clock-cells: Must be 0
+
+Exxample (R-Car H3):
+
+        usb2_clksel: clock-controller@e6590630 {
+                compatible = "renesas,r8a77950-rcar-usb2-clock-sel",
+                             "renesas,rcar-gen3-usb2-clock-sel";
+                reg = <0 0xe6590630 0 0x02>;
+                clocks = <&cpg CPG_MOD 703>, <&usb_extal>, <&usb_xtal>;
+                clock-names = "ehci_ohci", "usb_extal", "usb_xtal";