/* * Early serial console for 8250/16550 devices * * (c) Copyright 2004 Hewlett-Packard Development Company, L.P. * Bjorn Helgaas <bjorn.helgaas@hp.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License version 2 as * published by the Free Software Foundation. * * Based on the 8250.c serial driver, Copyright (C) 2001 Russell King, * and on early_printk.c by Andi Kleen. * * This is for use before the serial driver has initialized, in * particular, before the UARTs have been discovered and named. * Instead of specifying the console device as, e.g., "ttyS0", * we locate the device directly by its MMIO or I/O port address. * * The user can specify the device directly, e.g., * earlycon=uart8250,io,0x3f8,9600n8 * earlycon=uart8250,mmio,0xff5e0000,115200n8 * earlycon=uart8250,mmio32,0xff5e0000,115200n8 * or * console=uart8250,io,0x3f8,9600n8 * console=uart8250,mmio,0xff5e0000,115200n8 * console=uart8250,mmio32,0xff5e0000,115200n8 */ #include <linux/tty.h> #include <linux/init.h> #include <linux/console.h> #include <linux/serial_core.h> #include <linux/serial_reg.h> #include <linux/serial.h> #include <linux/serial_8250.h> #include <asm/io.h> #include <asm/serial.h> static struct earlycon_device *early_device; unsigned int __weak __init serial8250_early_in(struct uart_port *port, int offset) { switch (port->iotype) { case UPIO_MEM: return readb(port->membase + offset); case UPIO_MEM32: return readl(port->membase + (offset << 2)); case UPIO_PORT: return inb(port->iobase + offset); default: return 0; } } void __weak __init serial8250_early_out(struct uart_port *port, int offset, int value) { switch (port->iotype) { case UPIO_MEM: writeb(value, port->membase + offset); break; case UPIO_MEM32: writel(value, port->membase + (offset << 2)); break; case UPIO_PORT: outb(value, port->iobase + offset); break; } } #define BOTH_EMPTY (UART_LSR_TEMT | UART_LSR_THRE) static void __init wait_for_xmitr(struct uart_port *port) { unsigned int status; for (;;) { status = serial8250_early_in(port, UART_LSR); if ((status & BOTH_EMPTY) == BOTH_EMPTY) return; cpu_relax(); } } static void __init serial_putc(struct uart_port *port, int c) { wait_for_xmitr(port); serial8250_early_out(port, UART_TX, c); } static void __init early_serial8250_write(struct console *console, const char *s, unsigned int count) { struct uart_port *port = &early_device->port; unsigned int ier; /* Save the IER and disable interrupts */ ier = serial8250_early_in(port, UART_IER); serial8250_early_out(port, UART_IER, 0); uart_console_write(port, s, count, serial_putc); /* Wait for transmitter to become empty and restore the IER */ wait_for_xmitr(port); serial8250_early_out(port, UART_IER, ier); } static unsigned int __init probe_baud(struct uart_port *port) { unsigned char lcr, dll, dlm; unsigned int quot; lcr = serial8250_early_in(port, UART_LCR); serial8250_early_out(port, UART_LCR, lcr | UART_LCR_DLAB); dll = serial8250_early_in(port, UART_DLL); dlm = serial8250_early_in(port, UART_DLM); serial8250_early_out(port, UART_LCR, lcr); quot = (dlm << 8) | dll; return (port->uartclk / 16) / quot; } static void __init init_port(struct earlycon_device *device) { struct uart_port *port = &device->port; unsigned int divisor; unsigned char c; serial8250_early_out(port, UART_LCR, 0x3); /* 8n1 */ serial8250_early_out(port, UART_IER, 0); /* no interrupt */ serial8250_early_out(port, UART_FCR, 0); /* no fifo */ serial8250_early_out(port, UART_MCR, 0x3); /* DTR + RTS */ divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud); c = serial8250_early_in(port, UART_LCR); serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB); serial8250_early_out(port, UART_DLL, divisor & 0xff); serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff); serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB); } static int __init early_serial8250_setup(struct earlycon_device *device, const char *options) { if (!(device->port.membase || device->port.iobase)) return 0; if (!device->baud) { device->baud = probe_baud(&device->port); snprintf(device->options, sizeof(device->options), "%u", device->baud); } init_port(device); early_device = device; device->con->write = early_serial8250_write; return 0; } EARLYCON_DECLARE(uart8250, early_serial8250_setup); EARLYCON_DECLARE(uart, early_serial8250_setup); int __init setup_early_serial8250_console(char *cmdline) { char match[] = "uart8250"; if (cmdline && cmdline[4] == ',') match[4] = '\0'; return setup_earlycon(cmdline, match, early_serial8250_setup); } int serial8250_find_port_for_earlycon(void) { struct earlycon_device *device = early_device; struct uart_port *port = device ? &device->port : NULL; int line; int ret; if (!port || (!port->membase && !port->iobase)) return -ENODEV; line = serial8250_find_port(port); if (line < 0) return -ENODEV; ret = update_console_cmdline("uart", 8250, "ttyS", line, device->options); if (ret < 0) ret = update_console_cmdline("uart", 0, "ttyS", line, device->options); return ret; }