LXR linux/arch/mips/kernel/early_printk

   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
  12static void __iomem *serial8250_base;
  13static unsigned int serial8250_reg_shift;
  14static unsigned int serial8250_tx_timeout;
  15
  16void 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
  24static inline u8 serial_in(int offset)
  25{
  26        return readb(serial8250_base + (offset << serial8250_reg_shift));
  27}
  28
  29static inline void serial_out(int offset, char value)
  30{
  31        writeb(value, serial8250_base + (offset << serial8250_reg_shift));
  32}
  33
  34void 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