drivers/tty/serial/8250/8250_early.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Early serial console for 8250/16550 devices
 *
 * (c) Copyright 2004 Hewlett-Packard Development Company, L.P.
 *	Bjorn Helgaas <bjorn.helgaas@hp.com>
 *
 * 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/of.h>
#include <linux/serial_reg.h>
#include <linux/serial.h>
#include <linux/serial_8250.h>
#include <asm/io.h>
#include <asm/serial.h>

static unsigned int serial8250_early_in(struct uart_port *port, int offset)
{
	offset <<= port->regshift;

	switch (port->iotype) {
	case UPIO_MEM:
		return readb(port->membase + offset);
	case UPIO_MEM16:
		return readw(port->membase + offset);
	case UPIO_MEM32:
		return readl(port->membase + offset);
	case UPIO_MEM32BE:
		return ioread32be(port->membase + offset);
	case UPIO_PORT:
		return inb(port->iobase + offset);
	default:
		return 0;
	}
}

static void serial8250_early_out(struct uart_port *port, int offset, int value)
{
	offset <<= port->regshift;

	switch (port->iotype) {
	case UPIO_MEM:
		writeb(value, port->membase + offset);
		break;
	case UPIO_MEM16:
		writew(value, port->membase + offset);
		break;
	case UPIO_MEM32:
		writel(value, port->membase + offset);
		break;
	case UPIO_MEM32BE:
		iowrite32be(value, port->membase + offset);
		break;
	case UPIO_PORT:
		outb(value, port->iobase + offset);
		break;
	}
}

static void serial_putc(struct uart_port *port, unsigned char c)
{
	unsigned int status;

	serial8250_early_out(port, UART_TX, c);

	for (;;) {
		status = serial8250_early_in(port, UART_LSR);
		if (uart_lsr_tx_empty(status))
			break;
		cpu_relax();
	}
}

static void early_serial8250_write(struct console *console,
					const char *s, unsigned int count)
{
	struct earlycon_device *device = console->data;
	struct uart_port *port = &device->port;

	uart_console_write(port, s, count, serial_putc);
}

#ifdef CONFIG_CONSOLE_POLL
static int early_serial8250_read(struct console *console,
				 char *s, unsigned int count)
{
	struct earlycon_device *device = console->data;
	struct uart_port *port = &device->port;
	unsigned int status;
	int num_read = 0;

	while (num_read < count) {
		status = serial8250_early_in(port, UART_LSR);
		if (!(status & UART_LSR_DR))
			break;
		s[num_read++] = serial8250_early_in(port, UART_RX);
	}

	return num_read;
}
#else
#define early_serial8250_read NULL
#endif

static void __init init_port(struct earlycon_device *device)
{
	struct uart_port *port = &device->port;
	unsigned int divisor;
	unsigned char c;
	unsigned int ier;

	serial8250_early_out(port, UART_LCR, UART_LCR_WLEN8);		/* 8n1 */
	ier = serial8250_early_in(port, UART_IER);
	serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
	serial8250_early_out(port, UART_FCR, 0);	/* no fifo */
	serial8250_early_out(port, UART_MCR, UART_MCR_DTR | UART_MCR_RTS);

	if (port->uartclk) {
		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);
	}
}

int __init early_serial8250_setup(struct earlycon_device *device,
					 const char *options)
{
	if (!(device->port.membase || device->port.iobase))
		return -ENODEV;

	if (!device->baud) {
		struct uart_port *port = &device->port;
		unsigned int ier;

		/* assume the device was initialized, only mask interrupts */
		ier = serial8250_early_in(port, UART_IER);
		serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
	} else
		init_port(device);

	device->con->write = early_serial8250_write;
	device->con->read = early_serial8250_read;
	return 0;
}
EARLYCON_DECLARE(uart8250, early_serial8250_setup);
EARLYCON_DECLARE(uart, early_serial8250_setup);
OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);

#ifdef CONFIG_SERIAL_8250_OMAP

static int __init early_omap8250_setup(struct earlycon_device *device,
				       const char *options)
{
	struct uart_port *port = &device->port;

	if (!(device->port.membase || device->port.iobase))
		return -ENODEV;

	port->regshift = 2;
	device->con->write = early_serial8250_write;
	return 0;
}

OF_EARLYCON_DECLARE(omap8250, "ti,omap2-uart", early_omap8250_setup);
OF_EARLYCON_DECLARE(omap8250, "ti,omap3-uart", early_omap8250_setup);
OF_EARLYCON_DECLARE(omap8250, "ti,omap4-uart", early_omap8250_setup);

#endif