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_reg.h>
  33 #include <linux/serial.h>
  34 #include <linux/serial_8250.h>
  35 #include <asm/io.h>
  36 #include <asm/serial.h>
  37
  38 unsigned int __weak __init serial8250_early_in(struct uart_port *port, int offset)
  39 {
  40         switch (port->iotype) {
  41         case UPIO_MEM:
  42                 return readb(port->membase + offset);
  43         case UPIO_MEM32:
  44                 return readl(port->membase + (offset << 2));
  45         case UPIO_PORT:
  46                 return inb(port->iobase + offset);
  47         default:
  48                 return 0;
  49         }
  50 }
  51
  52 void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value)
  53 {
  54         switch (port->iotype) {
  55         case UPIO_MEM:
  56                 writeb(value, port->membase + offset);
  57                 break;
  58         case UPIO_MEM32:
  59                 writel(value, port->membase + (offset << 2));
  60                 break;
  61         case UPIO_PORT:
  62                 outb(value, port->iobase + offset);
  63                 break;
  64         }
  65 }
  66
  67 #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE)
  68
  69 static void __init wait_for_xmitr(struct uart_port *port)
  70 {
  71         unsigned int status;
  72
  73         for (;;) {
  74                 status = serial8250_early_in(port, UART_LSR);
  75                 if ((status & BOTH_EMPTY) == BOTH_EMPTY)
  76                         return;
  77                 cpu_relax();
  78         }
  79 }
  80
  81 static void __init serial_putc(struct uart_port *port, int c)
  82 {
  83         wait_for_xmitr(port);
  84         serial8250_early_out(port, UART_TX, c);
  85 }
  86
  87 static void __init early_serial8250_write(struct console *console,
  88                                         const char *s, unsigned int count)
  89 {
  90         struct earlycon_device *device = console->data;
  91         struct uart_port *port = &device->port;
  92         unsigned int ier;
  93
  94         /* Save the IER and disable interrupts preserving the UUE bit */
  95         ier = serial8250_early_in(port, UART_IER);
  96         if (ier)
  97                 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
  98
  99         uart_console_write(port, s, count, serial_putc);
 100
 101         /* Wait for transmitter to become empty and restore the IER */
 102         wait_for_xmitr(port);
 103
 104         if (ier)
 105                 serial8250_early_out(port, UART_IER, ier);
 106 }
 107
 108 static void __init init_port(struct earlycon_device *device)
 109 {
 110         struct uart_port *port = &device->port;
 111         unsigned int divisor;
 112         unsigned char c;
 113         unsigned int ier;
 114
 115         serial8250_early_out(port, UART_LCR, 0x3);      /* 8n1 */
 116         ier = serial8250_early_in(port, UART_IER);
 117         serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
 118         serial8250_early_out(port, UART_FCR, 0);        /* no fifo */
 119         serial8250_early_out(port, UART_MCR, 0x3);      /* DTR + RTS */
 120
 121         divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
 122         c = serial8250_early_in(port, UART_LCR);
 123         serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
 124         serial8250_early_out(port, UART_DLL, divisor & 0xff);
 125         serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
 126         serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
 127 }
 128
 129 static int __init early_serial8250_setup(struct earlycon_device *device,
 130                                          const char *options)
 131 {
 132         if (!(device->port.membase || device->port.iobase))
 133                 return -ENODEV;
 134
 135         if (!device->baud) {
 136                 struct uart_port *port = &device->port;
 137                 unsigned int ier;
 138
 139                 /* assume the device was initialized, only mask interrupts */
 140                 ier = serial8250_early_in(port, UART_IER);
 141                 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
 142         } else
 143                 init_port(device);
 144
 145         device->con->write = early_serial8250_write;
 146         return 0;
 147 }
 148 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 149 EARLYCON_DECLARE(uart, early_serial8250_setup);