early_printk_8250.c (1182B)
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}