aboutsummaryrefslogtreecommitdiffstats
path: root/arch/x86/boot/early_serial_console.c
diff options
context:
space:
mode:
Diffstat (limited to 'arch/x86/boot/early_serial_console.c')
-rw-r--r--arch/x86/boot/early_serial_console.c139
1 files changed, 139 insertions, 0 deletions
diff --git a/arch/x86/boot/early_serial_console.c b/arch/x86/boot/early_serial_console.c
new file mode 100644
index 0000000..030f4b9
--- /dev/null
+++ b/arch/x86/boot/early_serial_console.c
@@ -0,0 +1,139 @@
+#include "boot.h"
+
+#define DEFAULT_SERIAL_PORT 0x3f8 /* ttyS0 */
+
+#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
+
+static void early_serial_init(int port, int baud)
+{
+ unsigned char c;
+ unsigned divisor;
+
+ outb(0x3, port + LCR); /* 8n1 */
+ outb(0, port + IER); /* no interrupt */
+ outb(0, port + FCR); /* no fifo */
+ outb(0x3, port + MCR); /* DTR + RTS */
+
+ divisor = 115200 / baud;
+ c = inb(port + LCR);
+ outb(c | DLAB, port + LCR);
+ outb(divisor & 0xff, port + DLL);
+ outb((divisor >> 8) & 0xff, port + DLH);
+ outb(c & ~DLAB, port + LCR);
+
+ early_serial_base = port;
+}
+
+static void parse_earlyprintk(void)
+{
+ int baud = DEFAULT_BAUD;
+ char arg[32];
+ int pos = 0;
+ int port = 0;
+
+ if (cmdline_find_option("earlyprintk", arg, sizeof arg) > 0) {
+ char *e;
+
+ if (!strncmp(arg, "serial", 6)) {
+ port = DEFAULT_SERIAL_PORT;
+ pos += 6;
+ }
+
+ if (arg[pos] == ',')
+ pos++;
+
+ if (!strncmp(arg, "ttyS", 4)) {
+ static const int bases[] = { 0x3f8, 0x2f8 };
+ int idx = 0;
+
+ if (!strncmp(arg + pos, "ttyS", 4))
+ pos += 4;
+
+ if (arg[pos++] == '1')
+ idx = 1;
+
+ port = bases[idx];
+ }
+
+ if (arg[pos] == ',')
+ pos++;
+
+ baud = simple_strtoull(arg + pos, &e, 0);
+ if (baud == 0 || arg + pos == e)
+ baud = DEFAULT_BAUD;
+ }
+
+ if (port)
+ early_serial_init(port, baud);
+}
+
+#define BASE_BAUD (1843200/16)
+static unsigned int probe_baud(int port)
+{
+ unsigned char lcr, dll, dlh;
+ unsigned int quot;
+
+ lcr = inb(port + LCR);
+ outb(lcr | DLAB, port + LCR);
+ dll = inb(port + DLL);
+ dlh = inb(port + DLH);
+ outb(lcr, port + LCR);
+ quot = (dlh << 8) | dll;
+
+ return BASE_BAUD / quot;
+}
+
+static void parse_console_uart8250(void)
+{
+ char optstr[64], *options;
+ int baud = DEFAULT_BAUD;
+ int port = 0;
+
+ /*
+ * console=uart8250,io,0x3f8,115200n8
+ * need to make sure it is last one console !
+ */
+ if (cmdline_find_option("console", optstr, sizeof optstr) <= 0)
+ return;
+
+ options = optstr;
+
+ if (!strncmp(options, "uart8250,io,", 12))
+ port = simple_strtoull(options + 12, &options, 0);
+ else if (!strncmp(options, "uart,io,", 8))
+ port = simple_strtoull(options + 8, &options, 0);
+ else
+ return;
+
+ if (options && (options[0] == ','))
+ baud = simple_strtoull(options + 1, &options, 0);
+ else
+ baud = probe_baud(port);
+
+ if (port)
+ early_serial_init(port, baud);
+}
+
+void console_init(void)
+{
+ parse_earlyprintk();
+
+ if (!early_serial_base)
+ parse_console_uart8250();
+}