LXR linux/arch/mips/kernel/early_printk

   1/*
   2 *  8250/16550-type serial ports prom_putchar()
   3 *
   4 *  Copyright (C) 2010  Yoichi Yuasa <yuasa@linux-mips.org>
   5 *
   6 *  This program is free software; you can redistribute it and/or modify
   7 *  it under the terms of the GNU General Public License as published by
   8 *  the Free Software Foundation; either version 2 of the License, or
   9 *  (at your option) any later version.
  10 *
  11 *  This program is distributed in the hope that it will be useful,
  12 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 *  GNU General Public License for more details.
  15 *
  16 *  You should have received a copy of the GNU General Public License
  17 *  along with this program; if not, write to the Free Software
  18 *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  19 */
  20#include <linux/io.h>
  21#include <linux/serial_core.h>
  22#include <linux/serial_reg.h>
  23
  24static void __iomem *serial8250_base;
  25static unsigned int serial8250_reg_shift;
  26static unsigned int serial8250_tx_timeout;
  27
  28void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
  29                                  unsigned int timeout)
  30{
  31        serial8250_base = (void __iomem *)base;
  32        serial8250_reg_shift = reg_shift;
  33        serial8250_tx_timeout = timeout;
  34}
  35
  36static inline u8 serial_in(int offset)
  37{
  38        return readb(serial8250_base + (offset << serial8250_reg_shift));
  39}
  40
  41static inline void serial_out(int offset, char value)
  42{
  43        writeb(value, serial8250_base + (offset << serial8250_reg_shift));
  44}
  45
  46void prom_putchar(char c)
  47{
  48        unsigned int timeout;
  49        int status, bits;
  50
  51        if (!serial8250_base)
  52                return;
  53
  54        timeout = serial8250_tx_timeout;
  55        bits = UART_LSR_TEMT | UART_LSR_THRE;
  56
  57        do {
  58                status = serial_in(UART_LSR);
  59
  60                if (--timeout == 0)
  61                        break;
  62        } while ((status & bits) != bits);
  63
  64        if (timeout)
  65                serial_out(UART_TX, c);
  66}
  67