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_PORT:
  49                 return inb(port->iobase + offset);
  50         default:
  51                 return 0;
  52         }
  53 }
  54
  55 void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value)
  56 {
  57         switch (port->iotype) {
  58         case UPIO_MEM:
  59                 writeb(value, port->membase + offset);
  60                 break;
  61         case UPIO_MEM32:
  62                 writel(value, port->membase + (offset << 2));
  63                 break;
  64         case UPIO_PORT:
  65                 outb(value, port->iobase + offset);
  66                 break;
  67         }
  68 }
  69
  70 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
  71
  72 static void __init wait_for_xmitr(struct uart_port *port)
  73 {
  74         unsigned int status;
  75
  76         for (;;) {
  77                 status = serial8250_early_in(port, UART_LSR);
  78                 if ((status & BOTH_EMPTY) == BOTH_EMPTY)
  79                         return;
  80                 cpu_relax();
  81         }
  82 }
  83
  84 static void __init serial_putc(struct uart_port *port, int c)
  85 {
  86         wait_for_xmitr(port);
  87         serial8250_early_out(port, UART_TX, c);
  88 }
  89
  90 static void __init early_serial8250_write(struct console *console,
  91                                         const char *s, unsigned int count)
  92 {
  93         struct uart_port *port = &early_device->port;
  94         unsigned int ier;
  95
  96         /* Save the IER and disable interrupts */
  97         ier = serial8250_early_in(port, UART_IER);
  98         if (ier)
  99                 serial8250_early_out(port, UART_IER, 0);
 100
 101         uart_console_write(port, s, count, serial_putc);
 102
 103         /* Wait for transmitter to become empty and restore the IER */
 104         wait_for_xmitr(port);
 105
 106         if (ier)
 107                 serial8250_early_out(port, UART_IER, ier);
 108 }
 109
 110 static unsigned int __init probe_baud(struct uart_port *port)
 111 {
 112         unsigned char lcr, dll, dlm;
 113         unsigned int quot;
 114
 115         lcr = serial8250_early_in(port, UART_LCR);
 116         serial8250_early_out(port, UART_LCR, lcr | UART_LCR_DLAB);
 117         dll = serial8250_early_in(port, UART_DLL);
 118         dlm = serial8250_early_in(port, UART_DLM);
 119         serial8250_early_out(port, UART_LCR, lcr);
 120
 121         quot = (dlm << 8) | dll;
 122         return (port->uartclk / 16) / quot;
 123 }
 124
 125 static void __init init_port(struct earlycon_device *device)
 126 {
 127         struct uart_port *port = &device->port;
 128         unsigned int divisor;
 129         unsigned char c;
 130
 131         serial8250_early_out(port, UART_LCR, 0x3);      /* 8n1 */
 132         serial8250_early_out(port, UART_IER, 0);        /* no interrupt */
 133         serial8250_early_out(port, UART_FCR, 0);        /* no fifo */
 134         serial8250_early_out(port, UART_MCR, 0x3);      /* DTR + RTS */
 135
 136         divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
 137         c = serial8250_early_in(port, UART_LCR);
 138         serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
 139         serial8250_early_out(port, UART_DLL, divisor & 0xff);
 140         serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
 141         serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
 142 }
 143
 144 static int __init early_serial8250_setup(struct earlycon_device *device,
 145                                          const char *options)
 146 {
 147         if (!(device->port.membase || device->port.iobase))
 148                 return 0;
 149
 150         if (!device->baud) {
 151                 device->baud = probe_baud(&device->port);
 152                 snprintf(device->options, sizeof(device->options), "%u",
 153                          device->baud);
 154         }
 155
 156         init_port(device);
 157
 158         early_device = device;
 159         device->con->write = early_serial8250_write;
 160         return 0;
 161 }
 162 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 163 EARLYCON_DECLARE(uart, early_serial8250_setup);
 164
 165 int __init setup_early_serial8250_console(char *cmdline)
 166 {
 167         char match[] = "uart8250";
 168
 169         if (cmdline && cmdline[4] == ',')
 170                 match[4] = '\0';
 171
 172         return setup_earlycon(cmdline, match, early_serial8250_setup);
 173 }
 174
 175 int serial8250_find_port_for_earlycon(void)
 176 {
 177         struct earlycon_device *device = early_device;
 178         struct uart_port *port = device ? &device->port : NULL;
 179         int line;
 180         int ret;
 181
 182         if (!port || (!port->membase && !port->iobase))
 183                 return -ENODEV;
 184
 185         line = serial8250_find_port(port);
 186         if (line < 0)
 187                 return -ENODEV;
 188
 189         ret = update_console_cmdline("uart", 8250,
 190                              "ttyS", line, device->options);
 191         if (ret < 0)
 192                 ret = update_console_cmdline("uart", 0,
 193                                      "ttyS", line, device->options);
 194
 195         return ret;
 196 }