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Linux/arch/mips/kernel/early_printk_8250.c

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  1 // SPDX-License-Identifier: GPL-2.0-or-later
  2 /*
  3  *  8250/16550-type serial ports prom_putchar()
  4  *
  5  *  Copyright (C) 2010  Yoichi Yuasa <yuasa@linux-mips.org>
  6  */
  7 #include <linux/io.h>
  8 #include <linux/serial_core.h>
  9 #include <linux/serial_reg.h>
 10 #include <asm/setup.h>
 11 
 12 static void __iomem *serial8250_base;
 13 static unsigned int serial8250_reg_shift;
 14 static unsigned int serial8250_tx_timeout;
 15 
 16 void setup_8250_early_printk_port(unsigned long base, unsigned int reg_shift,
 17                                   unsigned int timeout)
 18 {
 19         serial8250_base = (void __iomem *)base;
 20         serial8250_reg_shift = reg_shift;
 21         serial8250_tx_timeout = timeout;
 22 }
 23 
 24 static inline u8 serial_in(int offset)
 25 {
 26         return readb(serial8250_base + (offset << serial8250_reg_shift));
 27 }
 28 
 29 static inline void serial_out(int offset, char value)
 30 {
 31         writeb(value, serial8250_base + (offset << serial8250_reg_shift));
 32 }
 33 
 34 void prom_putchar(char c)
 35 {
 36         unsigned int timeout;
 37         int status, bits;
 38 
 39         if (!serial8250_base)
 40                 return;
 41 
 42         timeout = serial8250_tx_timeout;
 43         bits = UART_LSR_TEMT | UART_LSR_THRE;
 44 
 45         do {
 46                 status = serial_in(UART_LSR);
 47 
 48                 if (--timeout == 0)
 49                         break;
 50         } while ((status & bits) != bits);
 51 
 52         if (timeout)
 53                 serial_out(UART_TX, c);
 54 }
 55 

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