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Linux/arch/x86/kernel/bootflag.c

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  1 /*
  2  *      Implement 'Simple Boot Flag Specification 2.0'
  3  */
  4 #include <linux/types.h>
  5 #include <linux/kernel.h>
  6 #include <linux/init.h>
  7 #include <linux/string.h>
  8 #include <linux/spinlock.h>
  9 #include <linux/acpi.h>
 10 #include <asm/io.h>
 11 
 12 #include <linux/mc146818rtc.h>
 13 
 14 #define SBF_RESERVED (0x78)
 15 #define SBF_PNPOS    (1<<0)
 16 #define SBF_BOOTING  (1<<1)
 17 #define SBF_DIAG     (1<<2)
 18 #define SBF_PARITY   (1<<7)
 19 
 20 int sbf_port __initdata = -1;   /* set via acpi_boot_init() */
 21 
 22 static int __init parity(u8 v)
 23 {
 24         int x = 0;
 25         int i;
 26 
 27         for (i = 0; i < 8; i++) {
 28                 x ^= (v & 1);
 29                 v >>= 1;
 30         }
 31 
 32         return x;
 33 }
 34 
 35 static void __init sbf_write(u8 v)
 36 {
 37         unsigned long flags;
 38 
 39         if (sbf_port != -1) {
 40                 v &= ~SBF_PARITY;
 41                 if (!parity(v))
 42                         v |= SBF_PARITY;
 43 
 44                 printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n",
 45                         sbf_port, v);
 46 
 47                 spin_lock_irqsave(&rtc_lock, flags);
 48                 CMOS_WRITE(v, sbf_port);
 49                 spin_unlock_irqrestore(&rtc_lock, flags);
 50         }
 51 }
 52 
 53 static u8 __init sbf_read(void)
 54 {
 55         unsigned long flags;
 56         u8 v;
 57 
 58         if (sbf_port == -1)
 59                 return 0;
 60 
 61         spin_lock_irqsave(&rtc_lock, flags);
 62         v = CMOS_READ(sbf_port);
 63         spin_unlock_irqrestore(&rtc_lock, flags);
 64 
 65         return v;
 66 }
 67 
 68 static int __init sbf_value_valid(u8 v)
 69 {
 70         if (v & SBF_RESERVED)           /* Reserved bits */
 71                 return 0;
 72         if (!parity(v))
 73                 return 0;
 74 
 75         return 1;
 76 }
 77 
 78 static int __init sbf_init(void)
 79 {
 80         u8 v;
 81 
 82         if (sbf_port == -1)
 83                 return 0;
 84 
 85         v = sbf_read();
 86         if (!sbf_value_valid(v)) {
 87                 printk(KERN_WARNING "Simple Boot Flag value 0x%x read from "
 88                         "CMOS RAM was invalid\n", v);
 89         }
 90 
 91         v &= ~SBF_RESERVED;
 92         v &= ~SBF_BOOTING;
 93         v &= ~SBF_DIAG;
 94 #if defined(CONFIG_ISAPNP)
 95         v |= SBF_PNPOS;
 96 #endif
 97         sbf_write(v);
 98 
 99         return 0;
100 }
101 module_init(sbf_init);
102 

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