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/* SPDX-License-Identifier: GPL-2.0-or-later */
/* Copyright (C) 2026 Richard Qin */
/*
* memblock.cc — Boot-time physical memory allocator
*
* Simple region tracker: one memory region (from FDT) plus an array
* of reserved regions. Allocation searches for gaps between reserved
* regions. All operations are O(n_reserved), which is fine for the
* ~20 allocations that happen during early boot.
*
* Reference: inspired by Linux kernel's mm/memblock.c
*/
#include <lume/memblock.h>
#include <lume/fdt.h>
#include <lume/klog.h>
#include <lume/kprintf.h>
#include <lume/addr.h>
extern "C" char _stext[], _kernel_end[];
/* ------------------------------------------------------------------ */
/* Module state */
/* ------------------------------------------------------------------ */
static struct {
uint64 mem_base;
uint64 mem_size;
struct {
uint64 base;
uint64 size;
} reserved[kMemblockMaxRegions];
int reserved_count;
bool active;
} g_mb;
/* ------------------------------------------------------------------ */
/* Internal helpers */
/* ------------------------------------------------------------------ */
/* Insert a reserved region, keeping the array sorted by base. */
static void insert_reserved(uint64 base, uint64 size)
{
if (g_mb.reserved_count >= kMemblockMaxRegions) {
kernel_panic("memblock: too many reserved regions");
}
int i = g_mb.reserved_count;
while (i > 0 && g_mb.reserved[i - 1].base > base) {
g_mb.reserved[i] = g_mb.reserved[i - 1];
i--;
}
g_mb.reserved[i] = {base, size};
g_mb.reserved_count++;
}
/* Check if [base, base+size) overlaps any reserved region. */
static bool overlaps_reserved(uint64 base, uint64 size)
{
uint64 end = base + size;
for (int i = 0; i < g_mb.reserved_count; i++) {
uint64 rb = g_mb.reserved[i].base;
uint64 re = rb + g_mb.reserved[i].size;
if (base < re && end > rb) {
return true;
}
}
return false;
}
/* Find the end of the first reserved region that covers `addr`. */
static uint64 reserved_end_covering(uint64 addr)
{
for (int i = 0; i < g_mb.reserved_count; i++) {
uint64 rb = g_mb.reserved[i].base;
uint64 re = rb + g_mb.reserved[i].size;
if (addr >= rb && addr < re) {
return re;
}
}
return addr;
}
/* ------------------------------------------------------------------ */
/* Public API */
/* ------------------------------------------------------------------ */
void memblock_init(uint64 fdt_paddr)
{
(void)fdt_paddr;
/* 1. Get memory layout from FDT */
uint64 mem_base = 0;
uint64 mem_size = 0;
fdt_early_get_mem_info(&mem_base, &mem_size);
if (mem_size == 0) {
kernel_panic("memblock_init: FDT reports zero memory");
}
g_mb.mem_base = mem_base;
g_mb.mem_size = mem_size;
g_mb.reserved_count = 0;
g_mb.active = true;
/* 2. Reserve firmware region [mem_base, kernel_start).
* OpenSBI occupies the first 2MB of RAM on RISC-V virt. */
uint64 ks_pa = va_to_pa(virt_addr(
reinterpret_cast<uint64>(_stext))).raw;
if (ks_pa > mem_base) {
memblock_reserve(mem_base, ks_pa - mem_base);
}
/* 3. Reserve kernel image [_stext, _kernel_end) */
uint64 ke_pa = va_to_pa(virt_addr(
reinterpret_cast<uint64>(_kernel_end))).raw;
memblock_reserve(ks_pa, ke_pa - ks_pa);
kprintf("[memblock] RAM [0x%llx, 0x%llx) = %llu MB\n",
mem_base, mem_base + mem_size, mem_size / (1024 * 1024));
kprintf("[memblock] kernel reserved [0x%llx, 0x%llx)\n", ks_pa, ke_pa);
}
void memblock_reserve(uint64 base, uint64 size)
{
uint64 aligned_base = page_align_down(base);
uint64 aligned_end = page_align_up(base + size);
insert_reserved(aligned_base, aligned_end - aligned_base);
}
uint64 memblock_alloc_top(uint64 size, uint64 align)
{
uint64 mem_end = g_mb.mem_base + g_mb.mem_size;
/* Search from top of RAM downward */
uint64 end = page_align_down(mem_end);
uint64 start = (end - size) & ~(align - 1);
while (start >= g_mb.mem_base && start + size <= mem_end) {
if (!overlaps_reserved(start, size)) {
memblock_reserve(start, size);
return start;
}
if (start < align) {
break;
}
start -= align;
}
kernel_panic("memblock_alloc_top: out of memory");
return 0;
}
uint64 memblock_alloc(uint64 size, uint64 align)
{
uint64 mem_end = g_mb.mem_base + g_mb.mem_size;
uint64 start = page_align_up(g_mb.mem_base);
while (start + size <= mem_end) {
start = (start + align - 1) & ~(align - 1);
if (start + size > mem_end) {
break;
}
if (!overlaps_reserved(start, size)) {
memblock_reserve(start, size);
return start;
}
/* Skip past the overlapping reserved region */
uint64 skip = reserved_end_covering(start);
if (skip <= start) {
start += align;
} else {
start = skip;
}
}
kernel_panic("memblock_alloc: out of memory");
return 0;
}
uint64 memblock_get_mem_base() { return g_mb.mem_base; }
uint64 memblock_get_mem_size() { return g_mb.mem_size; }
bool memblock_is_active() { return g_mb.active; }
void memblock_retire() { g_mb.active = false; }
void memblock_for_each_free(void (*cb)(uint64 base, uint64 size, void* ctx),
void* ctx)
{
uint64 pos = g_mb.mem_base;
uint64 mem_end = g_mb.mem_base + g_mb.mem_size;
for (int i = 0; i < g_mb.reserved_count && pos < mem_end; i++) {
uint64 rb = g_mb.reserved[i].base;
if (rb < pos) {
/* Overlapping/adjacent — skip */
uint64 re = g_mb.reserved[i].base + g_mb.reserved[i].size;
if (re > pos) {
pos = re;
}
continue;
}
if (rb > pos) {
/* Free gap [pos, rb) */
cb(pos, rb - pos, ctx);
}
pos = g_mb.reserved[i].base + g_mb.reserved[i].size;
}
/* Trailing free region after last reserved */
if (pos < mem_end) {
cb(pos, mem_end - pos, ctx);
}
}
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