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early_printk.c

/*
 * Early printk support for Microblaze.
 *
 * Copyright (C) 2007-2009 Michal Simek <monstr@monstr.eu>
 * Copyright (C) 2007-2009 PetaLogix
 * Copyright (C) 2003-2006 Yasushi SHOJI <yashi@atmark-techno.com>
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License. See the file "COPYING" in the main directory of this archive
 * for more details.
 */

#include <linux/console.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/tty.h>
#include <linux/io.h>
#include <asm/processor.h>
#include <linux/fcntl.h>
#include <asm/setup.h>
#include <asm/prom.h>

static u32 early_console_initialized;
static u32 base_addr;

static void early_printk_putc(char c)
{
      /*
       * Limit how many times we'll spin waiting for TX FIFO status.
       * This will prevent lockups if the base address is incorrectly
       * set, or any other issue on the UARTLITE.
       * This limit is pretty arbitrary, unless we are at about 10 baud
       * we'll never timeout on a working UART.
       */

      unsigned retries = 10000;
      /* read status bit - 0x8 offset */
      while (--retries && (in_be32(base_addr + 8) & (1 << 3)))
            ;

      /* Only attempt the iowrite if we didn't timeout */
      /* write to TX_FIFO - 0x4 offset */
      if (retries)
            out_be32(base_addr + 4, c & 0xff);
}

static void early_printk_write(struct console *unused,
                              const char *s, unsigned n)
{
      while (*s && n-- > 0) {
            early_printk_putc(*s);
            if (*s == '\n')
                  early_printk_putc('\r');
            s++;
      }
}

static struct console early_serial_console = {
      .name = "earlyser",
      .write = early_printk_write,
      .flags = CON_PRINTBUFFER,
      .index = -1,
};

static struct console *early_console = &early_serial_console;

void early_printk(const char *fmt, ...)
{
      char buf[512];
      int n;
      va_list ap;

      if (early_console_initialized) {
            va_start(ap, fmt);
            n = vscnprintf(buf, 512, fmt, ap);
            early_console->write(early_console, buf, n);
            va_end(ap);
      }
}

int __init setup_early_printk(char *opt)
{
      if (early_console_initialized)
            return 1;

      base_addr = early_uartlite_console();
      if (base_addr) {
            early_console_initialized = 1;
#ifdef CONFIG_MMU
            early_console_reg_tlb_alloc(base_addr);
#endif
            early_printk("early_printk_console is enabled at 0x%08x\n",
                                          base_addr);

            /* register_console(early_console); */

            return 0;
      } else
            return 1;
}

void __init disable_early_printk(void)
{
      if (!early_console_initialized || !early_console)
            return;
      printk(KERN_WARNING "disabling early console\n");
      unregister_console(early_console);
      early_console_initialized = 0;
}

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