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Linux/arch/mips/kernel/early_printk_8250.c

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  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 #include <asm/setup.h>
 24 
 25 static void __iomem *serial8250_base;
 26 static unsigned int serial8250_reg_shift;
 27 static unsigned int serial8250_tx_timeout;
 28 
 29 void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
 30                                   unsigned int timeout)
 31 {
 32         serial8250_base = (void __iomem *)base;
 33         serial8250_reg_shift = reg_shift;
 34         serial8250_tx_timeout = timeout;
 35 }
 36 
 37 static inline u8 serial_in(int offset)
 38 {
 39         return readb(serial8250_base + (offset << serial8250_reg_shift));
 40 }
 41 
 42 static inline void serial_out(int offset, char value)
 43 {
 44         writeb(value, serial8250_base + (offset << serial8250_reg_shift));
 45 }
 46 
 47 void prom_putchar(char c)
 48 {
 49         unsigned int timeout;
 50         int status, bits;
 51 
 52         if (!serial8250_base)
 53                 return;
 54 
 55         timeout = serial8250_tx_timeout;
 56         bits = UART_LSR_TEMT | UART_LSR_THRE;
 57 
 58         do {
 59                 status = serial_in(UART_LSR);
 60 
 61                 if (--timeout == 0)
 62                         break;
 63         } while ((status & bits) != bits);
 64 
 65         if (timeout)
 66                 serial_out(UART_TX, c);
 67 }
 68 

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