root/arch/x86/kernel/bootflag.c

DEFINITIONS

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

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