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
20int sbf_port __initdata = -1;	/* set via acpi_boot_init() */
21
22static 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
35static 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
53static 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
68static 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
78static 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}
101module_init(sbf_init);
102