1 files changed, 105 insertions, 6 deletions

diff --git a/arch/x86/boot/tty.c b/arch/x86/boot/tty.c
index 01ec69c901c7..f3ceee20ff12 100644
--- a/arch/x86/boot/tty.c
+++ b/arch/x86/boot/tty.c
@@ -10,23 +10,51 @@
  * ----------------------------------------------------------------------- */
 
 /*
- * Very simple screen I/O
- * XXX: Probably should add very simple serial I/O?
+ * Very simple screen and serial I/O
  */
 
 #include "boot.h"
 
+#define DEFAULT_SERIAL_PORT 0x3f8 /* ttyS0 */
+
+static int      early_serial_base;
+
+#define XMTRDY          0x20
+
+#define DLAB            0x80
+
+#define TXR             0       /*  Transmit register (WRITE) */
+#define RXR             0       /*  Receive register  (READ)  */
+#define IER             1       /*  Interrupt Enable          */
+#define IIR             2       /*  Interrupt ID              */
+#define FCR             2       /*  FIFO control              */
+#define LCR             3       /*  Line control              */
+#define MCR             4       /*  Modem control             */
+#define LSR             5       /*  Line Status               */
+#define MSR             6       /*  Modem Status              */
+#define DLL             0       /*  Divisor Latch Low         */
+#define DLH             1       /*  Divisor latch High        */
+
+#define DEFAULT_BAUD 9600
+
 /*
  * These functions are in .inittext so they can be used to signal
  * error during initialization.
  */
 
-void __attribute__((section(".inittext"))) putchar(int ch)
+static void __attribute__((section(".inittext"))) serial_putchar(int ch)
 {
-        struct biosregs ireg;
+        unsigned timeout = 0xffff;
 
-        if (ch == '\n')
-                putchar('\r');  /* \n -> \r\n */
+        while ((inb(early_serial_base + LSR) & XMTRDY) == 0 && --timeout)
+                cpu_relax();
+
+        outb(ch, early_serial_base + TXR);
+}
+
+static void __attribute__((section(".inittext"))) bios_putchar(int ch)
+{
+        struct biosregs ireg;
 
         initregs(&ireg);
         ireg.bx = 0x0007;
@@ -36,6 +64,17 @@ void __attribute__((section(".inittext"))) putchar(int ch)
         intcall(0x10, &ireg, NULL);
 }
 
+void __attribute__((section(".inittext"))) putchar(int ch)
+{
+        if (ch == '\n')
+                putchar('\r');  /* \n -> \r\n */
+
+        bios_putchar(ch);
+
+        if (early_serial_base != 0)
+                serial_putchar(ch);
+}
+
 void __attribute__((section(".inittext"))) puts(const char *str)
 {
         while (*str)
@@ -112,3 +151,63 @@ int getchar_timeout(void)
 
         return 0;               /* Timeout! */
 }
+
+static void early_serial_init(int baud)
+{
+        unsigned char c;
+        unsigned divisor;
+
+        outb(0x3, early_serial_base + LCR);     /* 8n1 */
+        outb(0, early_serial_base + IER);       /* no interrupt */
+        outb(0, early_serial_base + FCR);       /* no fifo */
+        outb(0x3, early_serial_base + MCR);     /* DTR + RTS */
+
+        divisor = 115200 / baud;
+        c = inb(early_serial_base + LCR);
+        outb(c | DLAB, early_serial_base + LCR);
+        outb(divisor & 0xff, early_serial_base + DLL);
+        outb((divisor >> 8) & 0xff, early_serial_base + DLH);
+        outb(c & ~DLAB, early_serial_base + LCR);
+}
+
+void console_init(void)
+{
+        int baud = DEFAULT_BAUD;
+        char arg[32];
+        int pos = 0;
+
+        if (cmdline_find_option("earlyprintk", arg, sizeof arg) > 0) {
+                char *e;
+
+                if (!strncmp(arg, "serial", 6)) {
+                        early_serial_base = DEFAULT_SERIAL_PORT;
+                        pos += 6;
+                }
+
+                if (arg[pos] == ',')
+                        pos++;
+
+                if (!strncmp(arg, "ttyS", 4)) {
+                        static const int bases[] = { 0x3f8, 0x2f8 };
+                        int port = 0;
+
+                        if (!strncmp(arg + pos, "ttyS", 4))
+                                pos += 4;
+
+                        if (arg[pos++] == '1')
+                                port = 1;
+
+                        early_serial_base = bases[port];
+                }
+
+                if (arg[pos] == ',')
+                        pos++;
+
+                baud = simple_strtoull(arg + pos, &e, 0);
+                if (baud == 0 || arg + pos == e)
+                        baud = DEFAULT_BAUD;
+        }
+
+        if (early_serial_base != 0)
+                early_serial_init(baud);
+}