raspberry-pi/4: Add touch support for official 7" display.

raspberry-pi/4/touch-ft5406.nix

@@ -0,0 +1,65 @@
+{ config, lib, ... }:
+
+let
+  cfg = config.hardware.raspberry-pi."4".touch-ft5406;
+in
+{
+  options.hardware = {
+    raspberry-pi."4".touch-ft5406 = {
+      enable = lib.mkEnableOption ''
+        Enable the touch controller of the official Raspberry Pi touch diplay.
+
+        The overlay is taken from the official Raspberry Pi Linux fork, and
+        the `compatible` field is updated to match the target device tree.
+        https://github.com/raspberrypi/linux/blob/14b35093ca68bf2c81bbc90aace5007142b40b40/arch/arm/boot/dts/overlays/rpi-ft5406-overlay.dts
+
+        For more information about the touch display, please refer to:
+        https://www.raspberrypi.com/documentation/accessories/display.html
+      '';
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Configure for modesetting in the device tree
+    hardware.deviceTree = {
+      overlays = [
+        # this *should* be equivalent to (which doesn't work):
+        # https://github.com/raspberrypi/linux/blob/rpi-5.10.y/arch/arm/boot/dts/overlays/dwc2-overlay.dts
+        # but actually it's obtained using
+        # dtc -I dtb -O dts ${config.hardware.deviceTree.kernelPackage}/dtbs/overlays/dwc2.dtbo
+        # (changes: modified top-level "compatible" field)
+        # which is slightly different and works
+        {
+          name = "rpi-ft5406-overlay";
+          dtsText = ''
+            /dts-v1/;
+            /plugin/;
+
+            / {
+            	compatible = "brcm,bcm2711";
+
+            	fragment@0 {
+            		target-path = "/soc/firmware";
+            		__overlay__ {
+            			ts: touchscreen {
+            				compatible = "raspberrypi,firmware-ts";
+            				touchscreen-size-x = <800>;
+            				touchscreen-size-y = <480>;
+            			};
+            		};
+            	};
+
+            	__overrides__ {
+            		touchscreen-size-x = <&ts>,"touchscreen-size-x:0";
+            		touchscreen-size-y = <&ts>,"touchscreen-size-y:0";
+            		touchscreen-inverted-x = <&ts>,"touchscreen-inverted-x?";
+            		touchscreen-inverted-y = <&ts>,"touchscreen-inverted-y?";
+            		touchscreen-swapped-x-y = <&ts>,"touchscreen-swapped-x-y?";
+                    };
+            };
+          '';
+        }
+      ];
+    };
+  };
+}