feat(hal): add riscv64's fdt

crates/eonix_hal/src/arch/riscv64/fdt.rs

@@ -0,0 +1,38 @@
+extern crate alloc;
+
+use alloc::string::String;
+
+use fdt::Fdt;
+use spin::Once;
+
+static GLOBAL_FDT: Once<Fdt<'static>> = Once::new();
+
+pub unsafe fn init_dtb_and_fdt(dtb_pa: usize) {
+    let dtb_virt_ptr = dtb_pa as *const u8;
+
+    GLOBAL_FDT.call_once(|| {
+        unsafe { Fdt::from_ptr(dtb_virt_ptr)
+            .expect("Failed to parse DTB from static memory.") }
+    });
+}
+
+pub fn get_global_fdt() -> &'static Fdt<'static> {
+    GLOBAL_FDT.get().expect("Global FDT has not been initialized yet")
+}
+
+#[derive(Debug, Clone)]
+pub struct HartInfo {
+    pub hart_id: usize,
+    pub compatible: Option<String>,
+}
+
+pub fn get_num_harts() -> usize {
+    let fdt = get_global_fdt();
+    let dtb_cpus = fdt.cpus();
+    let mut num_harts = 0;
+
+    for _cpu in dtb_cpus {
+        num_harts += 1;
+    }
+    num_harts
+}