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bootflag.c

/*
 *    Implement 'Simple Boot Flag Specification 2.0'
 */


#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/acpi.h>
#include <asm/io.h>

#include <linux/mc146818rtc.h>


#define SBF_RESERVED (0x78)
#define SBF_PNPOS    (1<<0)
#define SBF_BOOTING  (1<<1)
#define SBF_DIAG     (1<<2)
#define SBF_PARITY   (1<<7)


int sbf_port __initdata = -1; /* set via acpi_boot_init() */


static int __init parity(u8 v)
{
      int x = 0;
      int i;
      
      for(i=0;i<8;i++)
      {
            x^=(v&1);
            v>>=1;
      }
      return x;
}

static void __init sbf_write(u8 v)
{
      unsigned long flags;
      if(sbf_port != -1)
      {
            v &= ~SBF_PARITY;
            if(!parity(v))
                  v|=SBF_PARITY;

            printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n", sbf_port, v);

            spin_lock_irqsave(&rtc_lock, flags);
            CMOS_WRITE(v, sbf_port);
            spin_unlock_irqrestore(&rtc_lock, flags);
      }
}

static u8 __init sbf_read(void)
{
      u8 v;
      unsigned long flags;
      if(sbf_port == -1)
            return 0;
      spin_lock_irqsave(&rtc_lock, flags);
      v = CMOS_READ(sbf_port);
      spin_unlock_irqrestore(&rtc_lock, flags);
      return v;
}

static int __init sbf_value_valid(u8 v)
{
      if(v&SBF_RESERVED)            /* Reserved bits */
            return 0;
      if(!parity(v))
            return 0;
      return 1;
}

static int __init sbf_init(void)
{
      u8 v;
      if(sbf_port == -1)
            return 0;
      v = sbf_read();
      if(!sbf_value_valid(v))
            printk(KERN_WARNING "Simple Boot Flag value 0x%x read from CMOS RAM was invalid\n",v);

      v &= ~SBF_RESERVED;
      v &= ~SBF_BOOTING;
      v &= ~SBF_DIAG;
#if defined(CONFIG_ISAPNP)
      v |= SBF_PNPOS;
#endif
      sbf_write(v);
      return 0;
}

module_init(sbf_init);

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