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>

4 files changed, 165 insertions, 6 deletions

diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index 98239d2658f2..46c4c5c71af7 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -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)
 {
@@ -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;
@@ -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);
diff --git a/arch/x86/boot/main.c b/arch/x86/boot/main.c
index 140172b895bd..4ef1a33e8572 100644
--- a/arch/x86/boot/main.c
+++ b/arch/x86/boot/main.c
@@ -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();
 
diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c
index f94b7a0c2abf..aba29df4a7bb 100644
--- a/arch/x86/boot/string.c
+++ b/arch/x86/boot/string.c
@@ -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;
@@ -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;
+}
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);
+}