raspberry-pi/4: Add modesetting option

raspberry-pi/4/default.nix

@@ -1,6 +1,10 @@
 { lib, pkgs, ...}:
 
 {
+  imports = [
+    ./modesetting.nix
+  ];
+
   boot = {
     kernelPackages = lib.mkDefault pkgs.linuxPackages_rpi4;
     initrd.availableKernelModules = [ "usbhid" "usb_storage" "vc4" ];

raspberry-pi/4/modesetting.nix

@@ -0,0 +1,107 @@
+{ config, lib, pkgs, ... }:
+
+let
+  cfg = config.hardware.raspberry-pi."4".fkms-3d;
+in
+{
+  options.hardware = {
+    raspberry-pi."4".fkms-3d = {
+      enable = lib.mkEnableOption ''
+        Enable modesetting through fkms-3d
+      '';
+      cma = lib.mkOption {
+        type = lib.types.int;
+        default = 512;
+        description = ''
+          Amount of CMA (contiguous memory allocator) to reserve, in MiB.
+
+          The foundation overlay defaults to 256MiB, for backward compatibility.
+          As the Raspberry Pi 4 family of hardware has ample amount of memory, we
+          can reserve more without issue.
+
+          Additionally, reserving too much is not an issue. The kernel will use
+          CMA last if the memory is needed.
+        '';
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    # Configure for modesetting in the device tree
+    hardware.deviceTree = {
+      filter = "bcm2711-rpi-*.dtb";
+      overlays = [
+        # Equivalent to:
+        # https://github.com/raspberrypi/linux/blob/rpi-5.10.y/arch/arm/boot/dts/overlays/cma-overlay.dts
+        {
+          name = "rpi4-cma-overlay";
+          dtsText = ''
+            // SPDX-License-Identifier: GPL-2.0
+            /dts-v1/;
+            /plugin/;
+
+            / {
+              compatible = "brcm,bcm2711";
+
+              fragment@0 {
+                target = <&cma>;
+                __overlay__ {
+                  size = <(${toString cfg.cma} * 1024 * 1024)>;
+                };
+              };
+            };
+          '';
+        }
+        # Equivalent to:
+        # https://github.com/raspberrypi/linux/blob/rpi-5.10.y/arch/arm/boot/dts/overlays/vc4-fkms-v3d-overlay.dts
+        {
+          name = "rpi4-vc4-fkms-v3d-overlay";
+          dtsText = ''
+            // SPDX-License-Identifier: GPL-2.0
+            /dts-v1/;
+            /plugin/;
+
+            / {
+              compatible = "brcm,bcm2711";
+
+              fragment@1 {
+                target = <&fb>;
+                __overlay__ {
+                  status = "disabled";
+                };
+              };
+
+              fragment@2 {
+                target = <&firmwarekms>;
+                __overlay__ {
+                  status = "okay";
+                };
+              };
+
+              fragment@3 {
+                target = <&v3d>;
+                __overlay__ {
+                  status = "okay";
+                };
+              };
+
+              fragment@4 {
+                target = <&vc4>;
+                __overlay__ {
+                  status = "okay";
+                };
+              };
+            };
+          '';
+        }
+      ];
+    };
+
+    # Also configure the system for modesetting.
+
+    services.xserver.videoDrivers = lib.mkBefore [
+      "modesetting" # Prefer the modesetting driver in X11
+      "fbdev" # Fallback to fbdev
+    ];
+  };
+}