root/arch/x86/kernel/bootflag.c

DEFINITIONS

1. parity
2. sbf_write
3. sbf_read
4. sbf_value_valid
5. sbf_init

/*
 *      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)
{
        unsigned long flags;
        u8 v;

        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);