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

   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/of_device.h>
  31 #include <linux/serial_reg.h>
  32 #include <linux/serial.h>
  33 #include <linux/serial_8250.h>
  34 #include <asm/io.h>
  35 #include <asm/serial.h>
  36
  37 static unsigned int serial8250_early_in(struct uart_port *port, int offset)
  38 {
  39         offset <<= port->regshift;
  40
  41         switch (port->iotype) {
  42         case UPIO_MEM:
  43                 return readb(port->membase + offset);
  44         case UPIO_MEM16:
  45                 return readw(port->membase + offset);
  46         case UPIO_MEM32:
  47                 return readl(port->membase + offset);
  48         case UPIO_MEM32BE:
  49                 return ioread32be(port->membase + offset);
  50         case UPIO_PORT:
  51                 return inb(port->iobase + offset);
  52         default:
  53                 return 0;
  54         }
  55 }
  56
  57 static void serial8250_early_out(struct uart_port *port, int offset, int value)
  58 {
  59         offset <<= port->regshift;
  60
  61         switch (port->iotype) {
  62         case UPIO_MEM:
  63                 writeb(value, port->membase + offset);
  64                 break;
  65         case UPIO_MEM16:
  66                 writew(value, port->membase + offset);
  67                 break;
  68         case UPIO_MEM32:
  69                 writel(value, port->membase + offset);
  70                 break;
  71         case UPIO_MEM32BE:
  72                 iowrite32be(value, port->membase + offset);
  73                 break;
  74         case UPIO_PORT:
  75                 outb(value, port->iobase + offset);
  76                 break;
  77         }
  78 }
  79
  80 static void serial_putc(struct uart_port *port, unsigned char c)
  81 {
  82         unsigned int status;
  83
  84         serial8250_early_out(port, UART_TX, c);
  85
  86         for (;;) {
  87                 status = serial8250_early_in(port, UART_LSR);
  88                 if (uart_lsr_tx_empty(status))
  89                         break;
  90                 cpu_relax();
  91         }
  92 }
  93
  94 static void early_serial8250_write(struct console *console,
  95                                         const char *s, unsigned int count)
  96 {
  97         struct earlycon_device *device = console->data;
  98         struct uart_port *port = &device->port;
  99
 100         uart_console_write(port, s, count, serial_putc);
 101 }
 102
 103 #ifdef CONFIG_CONSOLE_POLL
 104 static int early_serial8250_read(struct console *console,
 105                                  char *s, unsigned int count)
 106 {
 107         struct earlycon_device *device = console->data;
 108         struct uart_port *port = &device->port;
 109         unsigned int status;
 110         int num_read = 0;
 111
 112         while (num_read < count) {
 113                 status = serial8250_early_in(port, UART_LSR);
 114                 if (!(status & UART_LSR_DR))
 115                         break;
 116                 s[num_read++] = serial8250_early_in(port, UART_RX);
 117         }
 118
 119         return num_read;
 120 }
 121 #else
 122 #define early_serial8250_read NULL
 123 #endif
 124
 125 static void __init init_port(struct earlycon_device *device)
 126 {
 127         struct uart_port *port = &device->port;
 128         unsigned int divisor;
 129         unsigned char c;
 130         unsigned int ier;
 131
 132         serial8250_early_out(port, UART_LCR, UART_LCR_WLEN8);           /* 8n1 */
 133         ier = serial8250_early_in(port, UART_IER);
 134         serial8250_early_out(port, UART_IER, ier & UART_IER_UUE); /* no interrupt */
 135         serial8250_early_out(port, UART_FCR, 0);        /* no fifo */
 136         serial8250_early_out(port, UART_MCR, UART_MCR_DTR | UART_MCR_RTS);
 137
 138         if (port->uartclk) {
 139                 divisor = DIV_ROUND_CLOSEST(port->uartclk, 16 * device->baud);
 140                 c = serial8250_early_in(port, UART_LCR);
 141                 serial8250_early_out(port, UART_LCR, c | UART_LCR_DLAB);
 142                 serial8250_early_out(port, UART_DLL, divisor & 0xff);
 143                 serial8250_early_out(port, UART_DLM, (divisor >> 8) & 0xff);
 144                 serial8250_early_out(port, UART_LCR, c & ~UART_LCR_DLAB);
 145         }
 146 }
 147
 148 int __init early_serial8250_setup(struct earlycon_device *device,
 149                                          const char *options)
 150 {
 151         if (!(device->port.membase || device->port.iobase))
 152                 return -ENODEV;
 153
 154         if (!device->baud) {
 155                 struct uart_port *port = &device->port;
 156                 unsigned int ier;
 157
 158                 /* assume the device was initialized, only mask interrupts */
 159                 ier = serial8250_early_in(port, UART_IER);
 160                 serial8250_early_out(port, UART_IER, ier & UART_IER_UUE);
 161         } else
 162                 init_port(device);
 163
 164         device->con->write = early_serial8250_write;
 165         device->con->read = early_serial8250_read;
 166         return 0;
 167 }
 168 EARLYCON_DECLARE(uart8250, early_serial8250_setup);
 169 EARLYCON_DECLARE(uart, early_serial8250_setup);
 170 OF_EARLYCON_DECLARE(ns16550, "ns16550", early_serial8250_setup);
 171 OF_EARLYCON_DECLARE(ns16550a, "ns16550a", early_serial8250_setup);
 172 OF_EARLYCON_DECLARE(uart, "nvidia,tegra20-uart", early_serial8250_setup);
 173 OF_EARLYCON_DECLARE(uart, "snps,dw-apb-uart", early_serial8250_setup);
 174
 175 #ifdef CONFIG_SERIAL_8250_OMAP
 176
 177 static int __init early_omap8250_setup(struct earlycon_device *device,
 178                                        const char *options)
 179 {
 180         struct uart_port *port = &device->port;
 181
 182         if (!(device->port.membase || device->port.iobase))
 183                 return -ENODEV;
 184
 185         port->regshift = 2;
 186         device->con->write = early_serial8250_write;
 187         return 0;
 188 }
 189
 190 OF_EARLYCON_DECLARE(omap8250, "ti,omap2-uart", early_omap8250_setup);
 191 OF_EARLYCON_DECLARE(omap8250, "ti,omap3-uart", early_omap8250_setup);
 192 OF_EARLYCON_DECLARE(omap8250, "ti,omap4-uart", early_omap8250_setup);
 193
 194 #endif