From 91df1f208c71c60dfaa457f2faf0ad4d2836b2ce Mon Sep 17 00:00:00 2001
From: Mel <mel@rnrd.eu>
Date: Sun, 27 Apr 2025 17:21:04 +0200
Subject: Add device tree overlay for ADS7846 touchscreen

Signed-off-by: Mel <mel@rnrd.eu>
---
 machines/fourmi/devices.nix  |   1 +
 modules/hardware/ads7846.nix | 104 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 105 insertions(+)
 create mode 100644 modules/hardware/ads7846.nix

diff --git a/machines/fourmi/devices.nix b/machines/fourmi/devices.nix
index de872a7..82342af 100644
--- a/machines/fourmi/devices.nix
+++ b/machines/fourmi/devices.nix
@@ -9,6 +9,7 @@
   # correctly configure hardware in this pi server.
   imports = [
     nixos-hardware.nixosModules.raspberry-pi-4
+    ../../modules/hardware/ads7846.nix
   ];
 
   # boot settings
diff --git a/modules/hardware/ads7846.nix b/modules/hardware/ads7846.nix
new file mode 100644
index 0000000..cf1131e
--- /dev/null
+++ b/modules/hardware/ads7846.nix
@@ -0,0 +1,104 @@
+{ ... }:
+
+{
+  hardware.deviceTree = {
+    overlays = [
+      {
+        name = "ads7846-overlay";
+        # taken from raspberry-pi kernel tree:
+        # https://github.com/raspberrypi/linux/blob/rpi-6.6.y/arch/arm/boot/dts/overlays/ads7846-overlay.dts
+        dtsText = ''
+          		  /*
+          		  * Generic Device Tree overlay for the ADS7846 touch controller
+          		  *
+          		  */
+
+          		  /dts-v1/;
+          		  /plugin/;
+
+          		  / {
+          			  compatible = "brcm,bcm2835";
+
+          			  fragment@0 {
+          				  target = <&spi0>;
+          				  __overlay__ {
+          					  status = "okay";
+          				  };
+          			  };
+
+          			  fragment@1 {
+          				  target = <&spidev0>;
+          				  __overlay__ {
+          					  status = "disabled";
+          				  };
+          			  };
+
+          			  fragment@2 {
+          				  target = <&spidev1>;
+          				  __overlay__ {
+          					  status = "disabled";
+          				  };
+          			  };
+
+          			  fragment@3 {
+          				  target = <&gpio>;
+          				  __overlay__ {
+          					  ads7846_pins: ads7846_pins {
+          						  brcm,pins = <255>; /* illegal default value */
+          						  brcm,function = <0>; /* in */
+          						  brcm,pull = <0>; /* none */
+          					  };
+          				  };
+          			  };
+
+          			  fragment@4 {
+          				  target = <&spi0>;
+          				  __overlay__ {
+          					  /* needed to avoid dtc warning */
+          					  #address-cells = <1>;
+          					  #size-cells = <0>;
+
+          					  ads7846: ads7846@1 {
+          						  compatible = "ti,ads7846";
+          						  reg = <1>;
+          						  pinctrl-names = "default";
+          						  pinctrl-0 = <&ads7846_pins>;
+
+          						  spi-max-frequency = <2000000>;
+          						  interrupts = <255 2>; /* high-to-low edge triggered */
+          						  interrupt-parent = <&gpio>;
+          						  pendown-gpio = <&gpio 255 1>;
+
+          						  /* driver defaults */
+          						  ti,x-min = /bits/ 16 <0>;
+          						  ti,y-min = /bits/ 16 <0>;
+          						  ti,x-max = /bits/ 16 <0x0FFF>;
+          						  ti,y-max = /bits/ 16 <0x0FFF>;
+          						  ti,pressure-min = /bits/ 16 <0>;
+          						  ti,pressure-max = /bits/ 16 <0xFFFF>;
+          						  ti,x-plate-ohms = /bits/ 16 <400>;
+          					  };
+          				  };
+          			  };
+          			  __overrides__ {
+          				  cs =     <&ads7846>,"reg:0";
+          				  speed =  <&ads7846>,"spi-max-frequency:0";
+          				  penirq = <&ads7846_pins>,"brcm,pins:0", /* REQUIRED */
+          					  <&ads7846>,"interrupts:0",
+          					  <&ads7846>,"pendown-gpio:4";
+          				  penirq_pull = <&ads7846_pins>,"brcm,pull:0";
+          				  swapxy = <&ads7846>,"ti,swap-xy?";
+          				  xmin =   <&ads7846>,"ti,x-min;0";
+          				  ymin =   <&ads7846>,"ti,y-min;0";
+          				  xmax =   <&ads7846>,"ti,x-max;0";
+          				  ymax =   <&ads7846>,"ti,y-max;0";
+          				  pmin =   <&ads7846>,"ti,pressure-min;0";
+          				  pmax =   <&ads7846>,"ti,pressure-max;0";
+          				  xohms =  <&ads7846>,"ti,x-plate-ohms;0";
+          			  };
+          		  };
+        '';
+      }
+    ];
+  };
+}
-- 
cgit 1.4.1