From 7f92ecc3b1dd01dd12c72ba17bc8bf1652495d2c Mon Sep 17 00:00:00 2001
From: Richard Qin <richard.qin.x@gmail.com>
Date: Wed, 13 May 2026 15:50:37 +0800
Subject: feat: enhance UART driver and FDT parser with MMU support and default
 UART settings

---
 na/drivers/uart.cc | 16 +++++++++++++---
 na/fdt/fdt.cc      | 12 +++++++++---
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/na/drivers/uart.cc b/na/drivers/uart.cc
index 2e553d6..264ec6a 100644
--- a/na/drivers/uart.cc
+++ b/na/drivers/uart.cc
@@ -16,6 +16,11 @@
 static uint64 g_uart_pa = 0;
 static uint64 g_uart_size = 0;
 static bool g_runtime_mapping_ready = false;
+static bool g_mmu_enabled = false;
+
+extern "C" void console_set_mmu_enabled() {
+    g_mmu_enabled = true;
+}
 
 extern "C" void early_putc(char c) {
     if (!g_uart_pa) return;
@@ -25,9 +30,14 @@ extern "C" void early_putc(char c) {
      * reachable via the bootstrap fixed direct map from entry.S.
      * After activation, switch to the runtime (possibly KASLR-slid) base.
      */
-    uint64 uart_va = g_runtime_mapping_ready
-                         ? pa_to_va(phys_addr(g_uart_pa)).raw
-                         : boot_pa_to_va(phys_addr(g_uart_pa)).raw;
+    uint64 uart_va = 0;
+    if (g_runtime_mapping_ready) {
+        uart_va = pa_to_va(phys_addr(g_uart_pa)).raw;
+    } else if (!g_mmu_enabled) {
+        uart_va = g_uart_pa;
+    } else {
+        uart_va = boot_pa_to_va(phys_addr(g_uart_pa)).raw;
+    }
 
     volatile auto* uart = reinterpret_cast<volatile uint8*>(uart_va);
     *uart = static_cast<uint8>(c);
diff --git a/na/fdt/fdt.cc b/na/fdt/fdt.cc
index fbec245..d44ebda 100644
--- a/na/fdt/fdt.cc
+++ b/na/fdt/fdt.cc
@@ -247,9 +247,16 @@ void FdtManager::early_scan_uart(uint64 fdt_paddr, uint64 *uart_addr,
   if (!uart_addr || !uart_size)
     return;
 
+  auto set_default_uart = [uart_addr, uart_size]() {
+    *uart_addr = 0x10000000ULL;
+    *uart_size = 0x100;
+  };
+
   const fdt_header *hdr = reinterpret_cast<const fdt_header *>(fdt_paddr);
-  if (bswap32(hdr->magic) != FDT_MAGIC)
+  if (bswap32(hdr->magic) != FDT_MAGIC) {
+    set_default_uart();
     return;
+  }
 
   const uint8 *dt_struct =
       reinterpret_cast<const uint8 *>(fdt_paddr) + bswap32(hdr->off_dt_struct);
@@ -343,8 +350,7 @@ void FdtManager::early_scan_uart(uint64 fdt_paddr, uint64 *uart_addr,
     }
   }
 
-  *uart_addr = 0;
-  *uart_size = 0;
+  set_default_uart();
 }
 
 /* ------------------------------------------------------------------ */
-- 
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