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 
parity(u8 v)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 
sbf_write(u8 v)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 
sbf_read(void)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 
sbf_value_valid(u8 v)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 
sbf_init(void)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