arch/mips/kernel/early_printk_8250.c

   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
  24 static void __iomem *serial8250_base;
  25 static unsigned int serial8250_reg_shift;
  26 static unsigned int serial8250_tx_timeout;
  27
  28 void 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
  36 static inline u8 serial_in(int offset)
  37 {
  38         return readb(serial8250_base + (offset << serial8250_reg_shift));
  39 }
  40
  41 static inline void serial_out(int offset, char value)
  42 {
  43         writeb(value, serial8250_base + (offset << serial8250_reg_shift));
  44 }
  45
  46 void 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 }