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Date: Sat, 10 Jul 2010 21:07:57 +0300
From: Pekka Enberg <penberg@...helsinki.fi>
To: hpa@...or.com
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
Pekka Enberg <penberg@...helsinki.fi>,
Ingo Molnar <mingo@...hat.com>,
Cyrill Gorcunov <gorcunov@...il.com>
Subject: [RFC/PATCH] x86: Early-boot serial I/O support
This patch adds serial I/O support to very early boot printf(). It's useful for
debugging boot code when running Linux under KVM, for example. The actual code
was lifted from early printk.
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Cyrill Gorcunov <gorcunov@...il.com>
Signed-off-by: Pekka Enberg <penberg@...helsinki.fi>
---
arch/x86/boot/boot.h | 1 +
arch/x86/boot/main.c | 3 ++
arch/x86/boot/tty.c | 65 +++++++++++++++++++++++++++++++++++++++++++++----
3 files changed, 63 insertions(+), 6 deletions(-)
diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 98239d2..5b37014 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -333,6 +333,7 @@ size_t strnlen(const char *s, size_t maxlen);
unsigned int atou(const char *s);
/* tty.c */
+void serial_init(void);
void puts(const char *);
void putchar(int);
int getchar(void);
diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c
index 140172b..1437efe 100644
--- a/arch/x86/boot/main.c
+++ b/arch/x86/boot/main.c
@@ -127,6 +127,9 @@ static void init_heap(void)
void main(void)
{
+ /* Initialize serial console */
+ serial_init();
+
/* First, copy the boot header into the "zeropage" */
copy_boot_params();
diff --git a/arch/x86/boot/tty.c b/arch/x86/boot/tty.c
index 01ec69c..2f0def5 100644
--- a/arch/x86/boot/tty.c
+++ b/arch/x86/boot/tty.c
@@ -10,8 +10,7 @@
* ----------------------------------------------------------------------- */
/*
- * Very simple screen I/O
- * XXX: Probably should add very simple serial I/O?
+ * Very simple screen and serial I/O
*/
#include "boot.h"
@@ -20,13 +19,58 @@
* These functions are in .inittext so they can be used to signal
* error during initialization.
*/
+static int early_serial_base = 0x3f8; /* ttyS0 */
-void __attribute__((section(".inittext"))) putchar(int ch)
+#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
+
+void __attribute__((section(".inittext"))) serial_init(void)
{
- struct biosregs ireg;
+ unsigned baud = DEFAULT_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);
+}
- if (ch == '\n')
- putchar('\r'); /* \n -> \r\n */
+static void __attribute__((section(".inittext"))) serial_putchar(int ch)
+{
+ unsigned timeout = 0xffff;
+
+ while ((inb(early_serial_base + LSR) & XMTRDY) == 0 && --timeout)
+ ;
+
+ 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 +80,15 @@ 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);
+ serial_putchar(ch);
+}
+
void __attribute__((section(".inittext"))) puts(const char *str)
{
while (*str)
--
1.6.3.3
--
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