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x86, setup: Early-boot serial I/O support
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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>
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Pekka Enberg authored and H. Peter Anvin committed Jul 12, 2010
1 parent 589643b commit fa97bdf
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Showing 4 changed files with 165 additions and 6 deletions.
16 changes: 16 additions & 0 deletions arch/x86/boot/boot.h
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,8 @@
extern struct setup_header hdr;
extern struct boot_params boot_params;

#define cpu_relax() asm volatile("rep; nop")

/* Basic port I/O */
static inline void outb(u8 v, u16 port)
{
Expand Down Expand Up @@ -203,6 +205,17 @@ static inline int isdigit(int ch)
return (ch >= '0') && (ch <= '9');
}

static inline int isxdigit(int ch)
{
if (isdigit(ch))
return true;

if ((ch >= 'a') && (ch <= 'f'))
return true;

return (ch >= 'A') && (ch <= 'F');
}

/* Heap -- available for dynamic lists. */
extern char _end[];
extern char *HEAP;
Expand Down Expand Up @@ -329,10 +342,13 @@ void initregs(struct biosregs *regs);

/* string.c */
int strcmp(const char *str1, const char *str2);
int strncmp(const char *cs, const char *ct, size_t count);
size_t strnlen(const char *s, size_t maxlen);
unsigned int atou(const char *s);
unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base);

/* tty.c */
void console_init(void);
void puts(const char *);
void putchar(int);
int getchar(void);
Expand Down
3 changes: 3 additions & 0 deletions arch/x86/boot/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -130,6 +130,9 @@ void main(void)
/* First, copy the boot header into the "zeropage" */
copy_boot_params();

/* Initialize the early-boot console */
console_init();

/* End of heap check */
init_heap();

Expand Down
41 changes: 41 additions & 0 deletions arch/x86/boot/string.c
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,22 @@ int strcmp(const char *str1, const char *str2)
return 0;
}

int strncmp(const char *cs, const char *ct, size_t count)
{
unsigned char c1, c2;

while (count) {
c1 = *cs++;
c2 = *ct++;
if (c1 != c2)
return c1 < c2 ? -1 : 1;
if (!c1)
break;
count--;
}
return 0;
}

size_t strnlen(const char *s, size_t maxlen)
{
const char *es = s;
Expand All @@ -48,3 +64,28 @@ unsigned int atou(const char *s)
i = i * 10 + (*s++ - '0');
return i;
}

/* Works only for digits and letters, but small and fast */
#define TOLOWER(x) ((x) | 0x20)

unsigned long long simple_strtoull(const char *cp, char **endp, unsigned int base)
{
unsigned long long result = 0;

if (base == 16 && cp[0] == '0' && TOLOWER(cp[1]) == 'x')
cp += 2;

while (isxdigit(*cp)) {
unsigned int value;

value = isdigit(*cp) ? *cp - '0' : TOLOWER(*cp) - 'a' + 10;
if (value >= base)
break;
result = result * base + value;
cp++;
}
if (endp)
*endp = (char *)cp;

return result;
}
111 changes: 105 additions & 6 deletions arch/x86/boot/tty.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand All @@ -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)
Expand Down Expand Up @@ -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);
}

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