arch/x86/kernel/bootflag.c

   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);