1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Early serial console for 8250/16550 devices
4 *
5 * (c) Copyright 2004 Hewlett-Packard Development Company, L.P.
6 *	Bjorn Helgaas <bjorn.helgaas@hp.com>
7 *
8 * Based on the 8250.c serial driver, Copyright (C) 2001 Russell King,
9 * and on early_printk.c by Andi Kleen.
10 *
11 * This is for use before the serial driver has initialized, in
12 * particular, before the UARTs have been discovered and named.
13 * Instead of specifying the console device as, e.g., "ttyS0",
14 * we locate the device directly by its MMIO or I/O port address.
15 *
16 * The user can specify the device directly, e.g.,
17 *	earlycon=uart8250,io,0x3f8,9600n8
18 *	earlycon=uart8250,mmio,0xff5e0000,115200n8
19 *	earlycon=uart8250,mmio32,0xff5e0000,115200n8
20 * or
21 *	console=uart8250,io,0x3f8,9600n8
22 *	console=uart8250,mmio,0xff5e0000,115200n8
23 *	console=uart8250,mmio32,0xff5e0000,115200n8
24 */
25
26#include <linux/tty.h>
27#include <linux/init.h>
28#include <linux/console.h>
29#include <linux/of.h>
30#include <linux/serial_reg.h>
31#include <linux/serial.h>
32#include <linux/serial_8250.h>
33#include <asm/io.h>
34#include <asm/serial.h>
35
36static unsigned int serial8250_early_in(struct uart_port *port, int offset)
37{
38	offset <<= port->regshift;
39
40	switch (port->iotype) {
41	case UPIO_MEM:
42		return readb(port->membase + offset);
43	case UPIO_MEM16:
44		return readw(port->membase + offset);
45	case UPIO_MEM32:
46		return readl(port->membase + offset);
47	case UPIO_MEM32BE:
48		return ioread32be(port->membase + offset);
49	case UPIO_PORT:
50		return inb(port->iobase + offset);
51	default:
52		return 0;
53	}
54}
55
56static void serial8250_early_out(struct uart_port *port, int offset, int value)
57{
58	offset <<= port->regshift;
59
60	switch (port->iotype) {
61	case UPIO_MEM:
62		writeb(value, port->membase + offset);
63		break;
64	case UPIO_MEM16:
65		writew(value, port->membase + offset);
66		break;
67	case UPIO_MEM32:
68		writel(value, port->membase + offset);
69		break;
70	case UPIO_MEM32BE:
71		iowrite32be(value, port->membase + offset);
72		break;
73	case UPIO_PORT:
74		outb(value, port->iobase + offset);
75		break;
76	}
77}
78
79static void serial_putc(struct uart_port *port, unsigned char c)
80{
81	unsigned int status;
82
83	serial8250_early_out(port, UART_TX, c);
84
85	for (;;) {
86		status = serial8250_early_in(port, UART_LSR);
87		if (uart_lsr_tx_empty(status))
88			break;
89		cpu_relax();
90	}
91}
92
93static void early_serial8250_write(struct console *console,
94					const char *s, unsigned int count)
95{
96	struct earlycon_device *device = console->data;
97	struct uart_port *port = &device->port;
98
99	uart_console_write(port, s, count, serial_putc);
100}
101
102#ifdef CONFIG_CONSOLE_POLL
103static int early_serial8250_read(struct console *console,
104				 char *s, unsigned int count)
105{
106	struct earlycon_device *device = console->data;
107	struct uart_port *port = &device->port;
108	unsigned int status;
109	int num_read = 0;
110
111	while (num_read < count) {
112		status = serial8250_early_in(port, UART_LSR);
113		if (!(status & UART_LSR_DR))
114			break;
115		s[num_read++] = serial8250_early_in(port, UART_RX);
116	}
117
118	return num_read;
119}
120#else
121#define early_serial8250_read NULL
122#endif
123
124static void __init init_port(struct earlycon_device *device)
125{
126	struct uart_port *port = &device->port;
127	unsigned int divisor;
128	unsigned char c;
129	unsigned int ier;
130
131	serial8250_early_out(port, UART_LCR, UART_LCR_WLEN8);		/* 8n1 */
132	ier = serial8250_early_in(port, UART_IER);
133	serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
134	serial8250_early_out(port, UART_FCR, 0);	/* no fifo */
135	serial8250_early_out(port, UART_MCR, UART_MCR_DTR | UART_MCR_RTS);
136
137	if (port->uartclk) {
138		divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
139		c = serial8250_early_in(port, UART_LCR);
140		serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
141		serial8250_early_out(port, UART_DLL, divisor & 0xff);
142		serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
143		serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
144	}
145}
146
147int __init early_serial8250_setup(struct earlycon_device *device,
148					 const char *options)
149{
150	if (!(device->port.membase || device->port.iobase))
151		return -ENODEV;
152
153	if (!device->baud) {
154		struct uart_port *port = &device->port;
155		unsigned int ier;
156
157		/* assume the device was initialized, only mask interrupts */
158		ier = serial8250_early_in(port, UART_IER);
159		serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
160	} else
161		init_port(device);
162
163	device->con->write = early_serial8250_write;
164	device->con->read = early_serial8250_read;
165	return 0;
166}
167EARLYCON_DECLARE(uart8250, early_serial8250_setup);
168EARLYCON_DECLARE(uart, early_serial8250_setup);
169OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
170OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
171OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
172OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
173
174#ifdef CONFIG_SERIAL_8250_OMAP
175
176static int __init early_omap8250_setup(struct earlycon_device *device,
177				       const char *options)
178{
179	struct uart_port *port = &device->port;
180
181	if (!(device->port.membase || device->port.iobase))
182		return -ENODEV;
183
184	port->regshift = 2;
185	device->con->write = early_serial8250_write;
186	return 0;
187}
188
189OF_EARLYCON_DECLARE(omap8250, "ti,omap2-uart", early_omap8250_setup);
190OF_EARLYCON_DECLARE(omap8250, "ti,omap3-uart", early_omap8250_setup);
191OF_EARLYCON_DECLARE(omap8250, "ti,omap4-uart", early_omap8250_setup);
192OF_EARLYCON_DECLARE(omap8250, "ti,am654-uart", early_omap8250_setup);
193
194#endif
195