bootflag.c

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/*
 *  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/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);