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 
36 static 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 
56 static 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 
79 static 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 
93 static 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
103 static 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 
124 static 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 
147 int __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 }
167 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
168 EARLYCON_DECLARE(uart, early_serial8250_setup);
169 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
170 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
171 OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
172 OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
173 
174 #ifdef CONFIG_SERIAL_8250_OMAP
175 
176 static 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 
189 OF_EARLYCON_DECLARE(omap8250, "ti,omap2-uart", early_omap8250_setup);
190 OF_EARLYCON_DECLARE(omap8250, "ti,omap3-uart", early_omap8250_setup);
191 OF_EARLYCON_DECLARE(omap8250, "ti,omap4-uart", early_omap8250_setup);
192 OF_EARLYCON_DECLARE(omap8250, "ti,am654-uart", early_omap8250_setup);
193 
194 #endif
195