LXR linux/arch/arm64/kernel/early

   1/*
   2 * Earlyprintk support.
   3 *
   4 * Copyright (C) 2012 ARM Ltd.
   5 * Author: Catalin Marinas <catalin.marinas@arm.com>
   6 *
   7 * This program is free software: you can redistribute it and/or modify
   8 * it under the terms of the GNU General Public License version 2 as
   9 * published by the Free Software Foundation.
  10 *
  11 * This program is distributed in the hope that it will be useful,
  12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 * GNU General Public License for more details.
  15 *
  16 * You should have received a copy of the GNU General Public License
  17 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  18 */
  19#include <linux/kernel.h>
  20#include <linux/console.h>
  21#include <linux/init.h>
  22#include <linux/string.h>
  23#include <linux/mm.h>
  24#include <linux/io.h>
  25
  26#include <linux/amba/serial.h>
  27#include <linux/serial_reg.h>
  28
  29static void __iomem *early_base;
  30static void (*printch)(char ch);
  31
  32/*
  33 * PL011 single character TX.
  34 */
  35static void pl011_printch(char ch)
  36{
  37        while (readl_relaxed(early_base + UART01x_FR) & UART01x_FR_TXFF)
  38                ;
  39        writeb_relaxed(ch, early_base + UART01x_DR);
  40        while (readl_relaxed(early_base + UART01x_FR) & UART01x_FR_BUSY)
  41                ;
  42}
  43
  44/*
  45 * Semihosting-based debug console
  46 */
  47static void smh_printch(char ch)
  48{
  49        asm volatile("mov  x1, %0\n"
  50                     "mov  x0, #3\n"
  51                     "hlt  0xf000\n"
  52                     : : "r" (&ch) : "x0", "x1", "memory");
  53}
  54
  55/*
  56 * 8250/16550 (8-bit aligned registers) single character TX.
  57 */
  58static void uart8250_8bit_printch(char ch)
  59{
  60        while (!(readb_relaxed(early_base + UART_LSR) & UART_LSR_THRE))
  61                ;
  62        writeb_relaxed(ch, early_base + UART_TX);
  63}
  64
  65/*
  66 * 8250/16550 (32-bit aligned registers) single character TX.
  67 */
  68static void uart8250_32bit_printch(char ch)
  69{
  70        while (!(readl_relaxed(early_base + (UART_LSR << 2)) & UART_LSR_THRE))
  71                ;
  72        writel_relaxed(ch, early_base + (UART_TX << 2));
  73}
  74
  75struct earlycon_match {
  76        const char *name;
  77        void (*printch)(char ch);
  78};
  79
  80static const struct earlycon_match earlycon_match[] __initconst = {
  81        { .name = "pl011", .printch = pl011_printch, },
  82        { .name = "smh", .printch = smh_printch, },
  83        { .name = "uart8250-8bit", .printch = uart8250_8bit_printch, },
  84        { .name = "uart8250-32bit", .printch = uart8250_32bit_printch, },
  85        {}
  86};
  87
  88static void early_write(struct console *con, const char *s, unsigned n)
  89{
  90        while (n-- > 0) {
  91                if (*s == '\n')
  92                        printch('\r');
  93                printch(*s);
  94                s++;
  95        }
  96}
  97
  98static struct console early_console_dev = {
  99        .name =         "earlycon",
 100        .write =        early_write,
 101        .flags =        CON_PRINTBUFFER | CON_BOOT,
 102        .index =        -1,
 103};
 104
 105/*
 106 * Parse earlyprintk=... parameter in the format:
 107 *
 108 *   <name>[,<addr>][,<options>]
 109 *
 110 * and register the early console. It is assumed that the UART has been
 111 * initialised by the bootloader already.
 112 */
 113static int __init setup_early_printk(char *buf)
 114{
 115        const struct earlycon_match *match = earlycon_match;
 116        phys_addr_t paddr = 0;
 117
 118        if (!buf) {
 119                pr_warning("No earlyprintk arguments passed.\n");
 120                return 0;
 121        }
 122
 123        while (match->name) {
 124                size_t len = strlen(match->name);
 125                if (!strncmp(buf, match->name, len)) {
 126                        buf += len;
 127                        break;
 128                }
 129                match++;
 130        }
 131        if (!match->name) {
 132                pr_warning("Unknown earlyprintk arguments: %s\n", buf);
 133                return 0;
 134        }
 135
 136        /* I/O address */
 137        if (!strncmp(buf, ",0x", 3)) {
 138                char *e;
 139                paddr = simple_strtoul(buf + 1, &e, 16);
 140                buf = e;
 141        }
 142        /* no options parsing yet */
 143
 144        if (paddr)
 145                early_base = early_io_map(paddr, EARLYCON_IOBASE);
 146
 147        printch = match->printch;
 148        early_console = &early_console_dev;
 149        register_console(&early_console_dev);
 150
 151        return 0;
 152}
 153
 154early_param("earlyprintk", setup_early_printk);
 155