Fix PMM for real HW + serial lock

src/io/serial/serial.c

@@ -6,9 +6,13 @@
  
 #include <kernel.h>
 #include <io/serial/serial.h>
+#include <sched/spinlock.h>
 
 extern struct init_status init;
 
+extern int panic_count;
+struct spinlock_t serial_lock = {0};
+
 /*
  * outb - Writes a byte to a CPU port
  * @port: CPU port to write to
@@ -85,9 +89,15 @@ static int is_transmit_empty()
  */
 void skputc(char c)
 {
-    // TODO: Spinlock here (serial access)
-    while (!is_transmit_empty()); // wait for free spot
-    outb(PORT, c);
+    if (panic_count == 0) {
+        spinlock_acquire(&serial_lock);
+        while (!is_transmit_empty()); // wait for free spot
+        outb(PORT, c);
+        spinlock_release(&serial_lock);
+    } else {
+        while (!is_transmit_empty());
+        outb(PORT, c);
+    }
 }
 
 /*