[Issue-62]: add dt overlay package

Signed-off-by: Jaymin Patel <jem.patel@gmail.com>

onion-dt-overlay/Makefile

@@ -0,0 +1,73 @@
+
+# Copyright (C) 2023 Onion Corporation
+# 
+# This is free software, licensed under the GNU General Public License v2.
+# See /LICENSE for more information.
+#
+
+include $(TOPDIR)/rules.mk
+include $(INCLUDE_DIR)/kernel.mk
+
+PKG_NAME:=onion-dt-overlay
+PKG_VERSION:=1.0
+PKG_RELEASE:=1
+KERNEL_BUILD_DIR ?= $(BUILD_DIR)/linux-$(BOARD)$(if $(SUBTARGET),_$(SUBTARGET))
+LINUX_DIR ?= $(KERNEL_BUILD_DIR)/linux-$(LINUX_VERSION)
+DTC=$(LINUX_DIR)/scripts/dtc/dtc
+
+include $(INCLUDE_DIR)/package.mk
+
+define Package/onion-dt-overlay/default
+	TITLE:=onion-dt-overlay
+	SECTION:=onion
+	CATEGORY:=Onion
+	SUBMENU:=Utilities
+	TITLE:=Onion DT Overlay
+endef
+
+define Package/onion-dt-overlay
+	$(Package/onion-dt-overlay/default)
+endef
+
+define Package/onion-dt-overlay/description
+	Onion DT Overlay
+endef
+
+define Build/Prepare
+	rm -rf $(PKG_BUILD_DIR)
+	mkdir -p $(PKG_BUILD_DIR)
+	$(CP) src $(PKG_BUILD_DIR)
+endef
+
+define Build/Compile
+	true
+endef
+
+define Package/onion-dt-overlay/install
+	true
+endef
+
+define BuildDtbo
+
+  define Package/onion-dt-overlay-$(1)
+	$(Package/onion-dt-overlay/default)
+	TITLE+= ($(1) DTBO)
+	DEPENDS+=onion-dt-overlay $(2)
+  endef
+
+  define Package/onion-dt-overlay-$(1)/description
+	$(3)
+  endef
+
+  define Package/onion-dt-overlay-$(1)/install
+	$(INSTALL_DIR) $$(1)/lib/firmware/device-tree/overlays/
+	$(DTC) -b 0 -@ -O dtb $(PKG_BUILD_DIR)/src/$(1).dts -o $(PKG_BUILD_DIR)/src/$(1).dtbo
+	$(INSTALL_DATA) $(PKG_BUILD_DIR)/src/$(1).dtbo $$(1)/lib/firmware/device-tree/overlays/$(1).dtbo
+  endef
+
+  $$(eval $$(call BuildPackage,onion-dt-overlay-$(1)))
+
+endef
+
+$(eval $(call BuildPackage,onion-dt-overlay))
+$(eval $(call BuildDtbo,sw-spi,,Provides SW SPI))

onion-dt-overlay/README.md

@@ -0,0 +1,38 @@
+## Device Tree Runtime Overlay
+
+onion-dt-overlay provides device tree runtime overlay without rebuilding firmware image giving flexibility to the user for easy customization of device tree.
+
+### Add custom device tree package.
+
+Onion Omega2 package onion-dt-overlay has a wrapper to build a device tree overlay package. Here are the steps that can be performed to add a custom device tree overlay.
+
+1. Add a custom `.dts` file into the `src` directory. Make sure the file extension is `.dts` only.
+2. Edit Makefile and add a new line after the last line
+
+```bash
+$(eval $(call BuildDtbo,<dtbo src file without ext>,<list of dependency packages>,<package description>))
+```
+### Example Dtbo
+
+Assume, the user wants to add a custom device tree runtime overlay package named `example`.
+- Create a file `src/example.dts`
+- Edit the Makefile of the onion-dt-overlay package and add a new line after the last line that looks like
+
+```bash
+$(eval $(call BuildDtbo,example,,Example DTBO))
+```
+
+It will create a new package named `onion-dt-overlay-example`.
+
+- After package is compiled and installed on omega2, it will install a `dtbo` file on location `/lib/firmware/device-tree/overlays/example.dtbo`.
+- reboot omega2.
+
+### Validate Runtime Dtbo
+
+- The status of `dtbo` can be check from a file `/sys/kernel/config/device-tree/overlays/<dtbo>/status`
+- In the case of `example.dtbo`, If would show its `status` as `applied`
+
+```bash
+# cat /sys/kernel/config/device-tree/overlays/example/status
+applied
+```

onion-dt-overlay/src/sw-spi.dts

@@ -0,0 +1,31 @@
+/dts-v1/;
+/plugin/;
+/ {
+  fragment@0 {
+    target-path = "/";
+    __overlay__ {
+      sw-spi {
+        compatible = "spi-gpio";
+        #address-cells = <0x1>;
+        #size-cells = <0x0>;
+        sck-gpios = <&gpio 11 0>;
+        mosi-gpios = <&gpio 5 0>;
+        miso-gpios = <&gpio 4 0>;
+        cs-gpios = <&gpio 23 0>;
+        num-chipselects = <1>;
+
+        spi-max-frequency = <100000>;
+        spi-cs-high;
+
+        /* clients */
+        spidev@0 {
+          compatible = "linux,spidev";
+          reg = <0>;
+          spi-max-frequency = <10000000>;
+        };
+
+      };
+
+    };
+  };
+};