arch/mips/kernel/early_printk_8250.c

   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 }