arch/arm64/kernel/early_printk.c

   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
  28 static void __iomem *early_base;
  29 static void (*printch)(char ch);
  30
  31 /*
  32  * PL011 single character TX.
  33  */
  34 static void pl011_printch(char ch)
  35 {
  36         while (readl_relaxed(early_base + UART01x_FR) & UART01x_FR_TXFF)
  37                 ;
  38         writeb_relaxed(ch, early_base + UART01x_DR);
  39         while (readl_relaxed(early_base + UART01x_FR) & UART01x_FR_BUSY)
  40                 ;
  41 }
  42
  43 struct earlycon_match {
  44         const char *name;
  45         void (*printch)(char ch);
  46 };
  47
  48 static const struct earlycon_match earlycon_match[] __initconst = {
  49         { .name = "pl011", .printch = pl011_printch, },
  50         {}
  51 };
  52
  53 static void early_write(struct console *con, const char *s, unsigned n)
  54 {
  55         while (n-- > 0) {
  56                 if (*s == '\n')
  57                         printch('\r');
  58                 printch(*s);
  59                 s++;
  60         }
  61 }
  62
  63 static struct console early_console = {
  64         .name =         "earlycon",
  65         .write =        early_write,
  66         .flags =        CON_PRINTBUFFER | CON_BOOT,
  67         .index =        -1,
  68 };
  69
  70 /*
  71  * Parse earlyprintk=... parameter in the format:
  72  *
  73  *   <name>[,<addr>][,<options>]
  74  *
  75  * and register the early console. It is assumed that the UART has been
  76  * initialised by the bootloader already.
  77  */
  78 static int __init setup_early_printk(char *buf)
  79 {
  80         const struct earlycon_match *match = earlycon_match;
  81         phys_addr_t paddr = 0;
  82
  83         if (!buf) {
  84                 pr_warning("No earlyprintk arguments passed.\n");
  85                 return 0;
  86         }
  87
  88         while (match->name) {
  89                 size_t len = strlen(match->name);
  90                 if (!strncmp(buf, match->name, len)) {
  91                         buf += len;
  92                         break;
  93                 }
  94                 match++;
  95         }
  96         if (!match->name) {
  97                 pr_warning("Unknown earlyprintk arguments: %s\n", buf);
  98                 return 0;
  99         }
 100
 101         /* I/O address */
 102         if (!strncmp(buf, ",0x", 3)) {
 103                 char *e;
 104                 paddr = simple_strtoul(buf + 1, &e, 16);
 105                 buf = e;
 106         }
 107         /* no options parsing yet */
 108
 109         if (paddr)
 110                 early_base = early_io_map(paddr, EARLYCON_IOBASE);
 111
 112         printch = match->printch;
 113         register_console(&early_console);
 114
 115         return 0;
 116 }
 117
 118 early_param("earlyprintk", setup_early_printk);