phy: rcar-gen3-usb2: add fallback binding

In the case of Renesas R-Car hardware we know that there are generations of
SoCs, e.g. Gen 2 and Gen 3. But beyond that its not clear what the
relationship between IP blocks might be. For example, I believe that
r8a7790 is older than r8a7791 but that doesn't imply that the latter is a
descendant of the former or vice versa.

We can, however, by examining the documentation and behaviour of the
hardware at run-time observe that the current driver implementation appears
to be compatible with the IP blocks on SoCs within a given generation.

For the above reasons and convenience when enabling new SoCs a
per-generation fallback compatibility string scheme being adopted for
drivers for Renesas SoCs.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>

Documentation/devicetree/bindings/phy/rcar-gen3-phy-usb2.txt

@@ -6,6 +6,12 @@ This file provides information on what the device node for the R-Car generation
 Required properties:
 - compatible: "renesas,usb2-phy-r8a7795" if the device is a part of an R8A7795
 	      SoC.
+	      "renesas,rcar-gen3-usb2-phy" 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 partial USB 2.0 Host register block.
 - clocks: clock phandle and specifier pair(s).
 - #phy-cells: see phy-bindings.txt in the same directory, must be <0>.
@@ -19,14 +25,14 @@ channel as USB OTG:
 Example (R-Car H3):
 
 	usb-phy@ee080200 {
-		compatible = "renesas,usb2-phy-r8a7795";
+		compatible = "renesas,usb2-phy-r8a7795", "renesas,rcar-gen3-usb2-phy";
 		reg = <0 0xee080200 0 0x700>;
 		interrupts = <GIC_SPI 108 IRQ_TYPE_LEVEL_HIGH>;
 		clocks = <&mstp7_clks R8A7795_CLK_EHCI0>;
 	};
 
 	usb-phy@ee0a0200 {
-		compatible = "renesas,usb2-phy-r8a7795";
+		compatible = "renesas,usb2-phy-r8a7795", "renesas,rcar-gen3-usb2-phy";
 		reg = <0 0xee0a0200 0 0x700>;
 		clocks = <&mstp7_clks R8A7795_CLK_EHCI0>;
 	};

drivers/phy/phy-rcar-gen3-usb2.c

@@ -251,6 +251,7 @@ static irqreturn_t rcar_gen3_phy_usb2_irq(int irq, void *_ch)
 
 static const struct of_device_id rcar_gen3_phy_usb2_match_table[] = {
 	{ .compatible = "renesas,usb2-phy-r8a7795" },
+	{ .compatible = "renesas,rcar-gen3-usb2-phy" },
 	{ }
 };
 MODULE_DEVICE_TABLE(of, rcar_gen3_phy_usb2_match_table);