Better serial management

Yay, I wrote my final information technology exam yesterday (abitur).
Only english and mathematics are left now - hype!! (sorry for polluting
my commit messages with useless personal news but this will affect the
future of Melvix as my free time and therefore the time that I'm working
on this project will increase massively once I'm finished with all my
exams)

3 files changed, 53 insertions, 13 deletions

diff --git a/kernel/drivers/serial.c b/kernel/drivers/serial.c
index c6172a6..e56c91b 100644
--- a/kernel/drivers/serial.c
+++ b/kernel/drivers/serial.c
@@ -1,31 +1,55 @@
 // MIT License, Copyright (c) 2020 Marvin Borner
 
+#include <assert.h>
 #include <cpu.h>
 #include <def.h>
 #include <serial.h>
 #include <str.h>
 
+#define PORT 0x3f8
+
+PROTECTED static u8 serial_enabled = 0;
+
+CLEAR void serial_disable(void)
+{
+	outb(PORT + 4, 0x1e); // Enable loopback
+	serial_enabled = 0;
+}
+
+CLEAR void serial_enable(void)
+{
+	outb(PORT + 4, 0x0f);
+	serial_enabled = 1;
+}
+
 CLEAR void serial_install(void)
 {
-	outb(0x3f8 + 1, 0x00);
-	outb(0x3f8 + 3, 0x80);
-	outb(0x3f8 + 0, 0x03);
-	outb(0x3f8 + 1, 0x00);
-	outb(0x3f8 + 3, 0x03);
-	outb(0x3f8 + 2, 0xC7);
-	outb(0x3f8 + 4, 0x0B);
+	outb(PORT + 1, 0x00);
+	outb(PORT + 3, 0x80);
+	outb(PORT + 0, 0x03);
+	outb(PORT + 1, 0x00);
+	outb(PORT + 3, 0x03);
+	outb(PORT + 2, 0xc7);
+
+	// Test serial chip
+	outb(PORT + 4, 0x1e); // Enable loopback
+	outb(PORT + 0, 0xae); // Write
+	assert(inb(PORT + 0) == 0xae); // Verify receive
 }
 
 static int is_transmit_empty(void)
 {
-	return inb(0x3f8 + 5) & 0x20;
+	return inb(PORT + 5) & 0x20;
 }
 
 void serial_put(char ch)
 {
+	if (!serial_enabled)
+		return;
+
 	while (is_transmit_empty() == 0)
 		;
-	outb(0x3f8, (u8)ch);
+	outb(PORT, (u8)ch);
 }
 
 void serial_print(const char *data)
diff --git a/kernel/inc/serial.h b/kernel/inc/serial.h
index e96316a..72c9dc1 100644
--- a/kernel/inc/serial.h
+++ b/kernel/inc/serial.h
@@ -6,6 +6,8 @@
 #include <def.h>
 
 void serial_install(void);
+void serial_enable(void);
+void serial_disable(void);
 void serial_print(const char *data) NONNULL;
 void serial_put(char ch);
 
diff --git a/kernel/multiboot.c b/kernel/multiboot.c
index 8fa7aa6..c99959c 100644
--- a/kernel/multiboot.c
+++ b/kernel/multiboot.c
@@ -2,20 +2,34 @@
 
 #include <assert.h>
 #include <def.h>
+#include <mem.h>
 #include <mm.h>
 #include <multiboot.h>
+#include <serial.h>
 
 PROTECTED static struct multiboot_info *info = NULL;
 
+CLEAR static void multiboot_parse_cmdline(const char *line)
+{
+	const char *start = line;
+	for (const char *p = line; p && *p; p++) {
+		if (*p == ' ')
+			start = p + 1;
+
+		if (memcmp(start, "log", 3) == 0) {
+			serial_enable();
+			start += 3;
+		}
+	}
+}
+
 CLEAR void multiboot_init(u32 magic, u32 addr)
 {
 	assert(magic == MULTIBOOT_MAGIC);
 	info = (void *)addr;
 
-	if (info->flags & MULTIBOOT_INFO_CMDLINE) {
-		// TODO: Do something useful with grub cmdline?
-		/* printf("CMDLINE: '%s'\n", info->cmdline); */
-	}
+	if (info->flags & MULTIBOOT_INFO_CMDLINE)
+		multiboot_parse_cmdline((const char *)info->cmdline);
 }
 
 CLEAR u32 multiboot_vbe(void)