Construct `IoMemAllocator` on RISC-V platforms

ostd/src/arch/riscv/io.rs

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: MPL-2.0
+
+use alloc::vec::Vec;
+
+use crate::{boot::memory_region::MemoryRegionType, io::IoMemAllocatorBuilder};
+
+/// Initializes the allocatable MMIO area based on the RISC-V memory
+/// distribution map.
+///
+/// Here we consider all the holes (filtering usable RAM) in the physical
+/// address space as MMIO regions.
+pub(super) fn construct_io_mem_allocator_builder() -> IoMemAllocatorBuilder {
+    let regions = &crate::boot::EARLY_INFO.get().unwrap().memory_regions;
+    let mut reserved_filter = regions.iter().filter(|r| {
+        r.typ() != MemoryRegionType::Unknown
+            && r.typ() != MemoryRegionType::Reserved
+            && r.typ() != MemoryRegionType::Framebuffer
+    });
+
+    let mut ranges = Vec::new();
+
+    let mut current_address = 0;
+    for region in reserved_filter {
+        if current_address < region.base() {
+            ranges.push(current_address..region.base());
+        }
+        current_address = region.end();
+    }
+    if current_address < usize::MAX {
+        ranges.push(current_address..usize::MAX);
+    }
+
+    // SAFETY: The range is guaranteed not to access physical memory.
+    unsafe { IoMemAllocatorBuilder::new(ranges) }
+}

ostd/src/arch/riscv/mod.rs

@@ -5,6 +5,7 @@
 pub mod boot;
 pub(crate) mod cpu;
 pub mod device;
+mod io;
 pub(crate) mod iommu;
 pub(crate) mod irq;
 pub(crate) mod mm;
@@ -24,6 +25,8 @@ pub(crate) unsafe fn late_init_on_bsp() {
     // SAFETY: This function is called in the boot context of the BSP.
     unsafe { trap::init() };
 
+    let io_mem_builder = io::construct_io_mem_allocator_builder();
+
     // SAFETY: We're on the BSP and we're ready to boot all APs.
     unsafe { crate::boot::smp::boot_all_aps() };
 
@@ -32,6 +35,11 @@ pub(crate) unsafe fn late_init_on_bsp() {
     // been performed.
     unsafe { timer::init() };
     let _ = pci::init();
+
+    // SAFETY:
+    // 1. All the system device memory have been removed from the builder.
+    // 2. RISC-V platforms do not have port I/O.
+    unsafe { crate::io::init(io_mem_builder) };
 }
 
 pub(crate) unsafe fn init_on_ap() {