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/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
 193 #endif