rt-thread/components/drivers/ofw/Kconfig

menuconfig RT_USING_OFW
    bool "Using Open Firmware (OFW)"
    select RT_USING_ADT
    select RT_USING_ADT_REF
    select RT_USING_ADT_BITMAP
    select RT_USING_MEMBLOCK
    depends on RT_USING_DM
    default n
    help
        Enable Open Firmware (Device Tree) support.
        
        OFW/Device Tree provides hardware description separate from code:
        - Flattened Device Tree (FDT/DTB) parsing
        - Hardware discovery and configuration
        - Platform-independent device drivers
        - Runtime hardware detection
        
        Features:
        - Standard device tree bindings
        - Property parsing and access
        - Node traversal and searching
        - Phandle reference resolution
        - Address translation
        - Interrupt mapping
        
        Benefits:
        - Single kernel binary for multiple boards
        - Easier board porting (just change DTB)
        - Better hardware abstraction
        - Industry-standard hardware description
        
        Use cases:
        - ARM/RISC-V systems with complex hardware
        - Supporting multiple board variants
        - Dynamic hardware configuration
        - PCI, USB, network device enumeration
        
        Requires:
        - RT_USING_DM (Device Model)
        - Memory block allocator
        - Abstract Data Types (ADT) support
        
        Essential for modern ARM Cortex-A and RISC-V systems.
        Enable for device tree-based hardware discovery.

config RT_USING_BUILTIN_FDT
    bool "Using builtin fdt in kernel"
    depends on RT_USING_OFW
    default n
    help
        Embed Flattened Device Tree (FDT) binary into kernel image.
        
        When enabled:
        - DTB file linked into kernel binary
        - No need for bootloader to pass DTB
        - DTB always available at boot
        
        Advantages:
        + Simpler boot process
        + No DTB location dependencies
        + Guaranteed DTB availability
        
        Disadvantages:
        - Larger kernel image
        - Must rebuild kernel to change DTB
        - Less flexible than bootloader-provided DTB
        
        Typical use:
        - Systems without proper bootloader
        - Debugging and development
        - Single-board configurations
        
        Alternative: Have bootloader pass DTB address to kernel.
        
        Enable for embedded DTB in kernel image.

config RT_BUILTIN_FDT_PATH
    string "Builtin fdt path, will rebuild if have dts"
    depends on RT_USING_BUILTIN_FDT
    default "rtthread.dtb"
    help
        Path to the compiled Device Tree Blob (DTB) file to embed.
        
        Default: "rtthread.dtb"
        
        This file is included in the kernel binary during linking.
        
        Workflow:
        1. Write device tree source (.dts file)
        2. Compile to DTB: dtc -I dts -O dtb -o rtthread.dtb rtthread.dts
        3. Set this path to the DTB location
        4. Rebuild kernel (DTB will be embedded)
        
        Path can be:
        - Relative to build directory
        - Absolute path
        
        Kernel will automatically rebuild if DTS changes (if build system configured).

config RT_FDT_EARLYCON_MSG_SIZE
    int "Earlycon message buffer size (KB)"
    depends on RT_USING_OFW
    default 128
    help
        Size of early console message buffer in kilobytes.
        
        Default: 128 KB
        
        Early console (earlycon) provides debug output before full console initialization:
        - Available during early boot
        - Before full UART driver loads
        - Critical for debugging boot failures
        
        Buffer stores messages when:
        - Console not yet available
        - Output faster than transmission
        
        Larger buffer:
        + More boot messages captured
        + Better for verbose debugging
        - More memory usage
        
        Smaller buffer:
        + Less memory overhead
        - May lose early messages
        
        Increase for detailed boot debugging.
        Decrease to save memory if earlycon not critical.

config RT_USING_OFW_BUS_RANGES_NUMBER
    int "Max bus ranges number"
    depends on RT_USING_OFW
    default 8 if ARCH_CPU_64BIT
    default 4
    help
        Maximum number of bus address ranges for device tree translation.
        
        Default:
        - 64-bit systems: 8 ranges
        - 32-bit systems: 4 ranges
        
        Bus ranges define address space mappings:
        - CPU address to device bus address
        - PCI memory/IO spaces
        - Different bus protocols (AHB, APB, AXI)
        
        Each range describes a memory window mapping.
        
        Typical usage:
        - PCI: 2-3 ranges (prefetchable mem, non-prefetchable mem, I/O)
        - Complex SoCs: 4-8 ranges for different buses
        
        Increase for:
        - Complex bus hierarchies
        - Multiple PCI buses
        - Systems with many address spaces
        
        Each range uses ~32-48 bytes of memory.
        Set based on your SoC's bus complexity.