drivers/tty/serial/8250/8250_early.c

   1 /*
   2  * Early serial console for 8250/16550 devices
   3  *
   4  * (c) Copyright 2004 Hewlett-Packard Development Company, L.P.
   5  *      Bjorn Helgaas <bjorn.helgaas@hp.com>
   6  *
   7  * This program is free software; you can redistribute it and/or modify
   8  * it under the terms of the GNU General Public License version 2 as
   9  * published by the Free Software Foundation.
  10  *
  11  * Based on the 8250.c serial driver, Copyright (C) 2001 Russell King,
  12  * and on early_printk.c by Andi Kleen.
  13  *
  14  * This is for use before the serial driver has initialized, in
  15  * particular, before the UARTs have been discovered and named.
  16  * Instead of specifying the console device as, e.g., "ttyS0",
  17  * we locate the device directly by its MMIO or I/O port address.
  18  *
  19  * The user can specify the device directly, e.g.,
  20  *      earlycon=uart8250,io,0x3f8,9600n8
  21  *      earlycon=uart8250,mmio,0xff5e0000,115200n8
  22  *      earlycon=uart8250,mmio32,0xff5e0000,115200n8
  23  * or
  24  *      console=uart8250,io,0x3f8,9600n8
  25  *      console=uart8250,mmio,0xff5e0000,115200n8
  26  *      console=uart8250,mmio32,0xff5e0000,115200n8
  27  */
  28
  29 #include <linux/tty.h>
  30 #include <linux/init.h>
  31 #include <linux/console.h>
  32 #include <linux/serial_core.h>
  33 #include <linux/serial_reg.h>
  34 #include <linux/serial.h>
  35 #include <linux/serial_8250.h>
  36 #include <asm/io.h>
  37 #include <asm/serial.h>
  38
  39 static struct earlycon_device *early_device;
  40
  41 unsigned int __weak __init serial8250_early_in(struct uart_port *port, int offset)
  42 {
  43         switch (port->iotype) {
  44         case UPIO_MEM:
  45                 return readb(port->membase + offset);
  46         case UPIO_MEM32:
  47                 return readl(port->membase + (offset << 2));
  48         case UPIO_MEM32BE:
  49                 return ioread32be(port->membase + (offset << 2));
  50         case UPIO_PORT:
  51                 return inb(port->iobase + offset);
  52         default:
  53                 return 0;
  54         }
  55 }
  56
  57 void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value)
  58 {
  59         switch (port->iotype) {
  60         case UPIO_MEM:
  61                 writeb(value, port->membase + offset);
  62                 break;
  63         case UPIO_MEM32:
  64                 writel(value, port->membase + (offset << 2));
  65                 break;
  66         case UPIO_MEM32BE:
  67                 iowrite32be(value, port->membase + (offset << 2));
  68                 break;
  69         case UPIO_PORT:
  70                 outb(value, port->iobase + offset);
  71                 break;
  72         }
  73 }
  74
  75 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
  76
  77 static void __init wait_for_xmitr(struct uart_port *port)
  78 {
  79         unsigned int status;
  80
  81         for (;;) {
  82                 status = serial8250_early_in(port, UART_LSR);
  83                 if ((status & BOTH_EMPTY) == BOTH_EMPTY)
  84                         return;
  85                 cpu_relax();
  86         }
  87 }
  88
  89 static void __init serial_putc(struct uart_port *port, int c)
  90 {
  91         wait_for_xmitr(port);
  92         serial8250_early_out(port, UART_TX, c);
  93 }
  94
  95 static void __init early_serial8250_write(struct console *console,
  96                                         const char *s, unsigned int count)
  97 {
  98         struct uart_port *port = &early_device->port;
  99         unsigned int ier;
 100
 101         /* Save the IER and disable interrupts preserving the UUE bit */
 102         ier = serial8250_early_in(port, UART_IER);
 103         if (ier)
 104                 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
 105
 106         uart_console_write(port, s, count, serial_putc);
 107
 108         /* Wait for transmitter to become empty and restore the IER */
 109         wait_for_xmitr(port);
 110
 111         if (ier)
 112                 serial8250_early_out(port, UART_IER, ier);
 113 }
 114
 115 static unsigned int __init probe_baud(struct uart_port *port)
 116 {
 117         unsigned char lcr, dll, dlm;
 118         unsigned int quot;
 119
 120         lcr = serial8250_early_in(port, UART_LCR);
 121         serial8250_early_out(port, UART_LCR, lcr | UART_LCR_DLAB);
 122         dll = serial8250_early_in(port, UART_DLL);
 123         dlm = serial8250_early_in(port, UART_DLM);
 124         serial8250_early_out(port, UART_LCR, lcr);
 125
 126         quot = (dlm << 8) | dll;
 127         return (port->uartclk / 16) / quot;
 128 }
 129
 130 static void __init init_port(struct earlycon_device *device)
 131 {
 132         struct uart_port *port = &device->port;
 133         unsigned int divisor;
 134         unsigned char c;
 135         unsigned int ier;
 136
 137         serial8250_early_out(port, UART_LCR, 0x3);      /* 8n1 */
 138         ier = serial8250_early_in(port, UART_IER);
 139         serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
 140         serial8250_early_out(port, UART_FCR, 0);        /* no fifo */
 141         serial8250_early_out(port, UART_MCR, 0x3);      /* DTR + RTS */
 142
 143         divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
 144         c = serial8250_early_in(port, UART_LCR);
 145         serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
 146         serial8250_early_out(port, UART_DLL, divisor & 0xff);
 147         serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
 148         serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
 149 }
 150
 151 static int __init early_serial8250_setup(struct earlycon_device *device,
 152                                          const char *options)
 153 {
 154         if (!(device->port.membase || device->port.iobase))
 155                 return 0;
 156
 157         if (!device->baud) {
 158                 device->baud = probe_baud(&device->port);
 159                 snprintf(device->options, sizeof(device->options), "%u",
 160                          device->baud);
 161         }
 162
 163         init_port(device);
 164
 165         early_device = device;
 166         device->con->write = early_serial8250_write;
 167         return 0;
 168 }
 169 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 170 EARLYCON_DECLARE(uart, early_serial8250_setup);
 171
 172 int __init setup_early_serial8250_console(char *cmdline)
 173 {
 174         char match[] = "uart8250";
 175
 176         if (cmdline && cmdline[4] == ',')
 177                 match[4] = '\0';
 178
 179         return setup_earlycon(cmdline, match, early_serial8250_setup);
 180 }
 181
 182 int serial8250_find_port_for_earlycon(void)
 183 {
 184         struct earlycon_device *device = early_device;
 185         struct uart_port *port = device ? &device->port : NULL;
 186         int line;
 187         int ret;
 188
 189         if (!port || (!port->membase && !port->iobase))
 190                 return -ENODEV;
 191
 192         line = serial8250_find_port(port);
 193         if (line < 0)
 194                 return -ENODEV;
 195
 196         ret = update_console_cmdline("uart", 8250,
 197                              "ttyS", line, device->options);
 198         if (ret < 0)
 199                 ret = update_console_cmdline("uart", 0,
 200                                      "ttyS", line, device->options);
 201
 202         return ret;
 203 }