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authorPekka Enberg <penberg@cs.helsinki.fi>2010-07-11 11:06:57 +0300
committerH. Peter Anvin <hpa@linux.intel.com>2010-07-12 14:46:00 -0700
commitfa97bdf92709adaaf8b9a5164a895e262a4fcf60 (patch)
treee34f1b6232c302e39065f3dd7ef8bbf4c8ac3d3d /arch/x86/boot/tty.c
parent589643be6693c46fbc54bae77745f336c8ed4bcc (diff)
x86, setup: Early-boot serial I/O support
This patch adds serial I/O support to the real-mode setup (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: Cyrill Gorcunov <gorcunov@gmail.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Yinghai Lu <yinghai@kernel.org> Signed-off-by: Pekka Enberg <penberg@cs.helsinki.fi> LKML-Reference: <1278835617-11368-1-git-send-email-penberg@cs.helsinki.fi> Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/boot/tty.c')
-rw-r--r--arch/x86/boot/tty.c111
1 files changed, 105 insertions, 6 deletions
diff --git a/arch/x86/boot/tty.c b/arch/x86/boot/tty.c
index 01ec69c901c..f3ceee20ff1 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);
+}