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
21int sbf_port __initdata = -1;	/* set via acpi_boot_init() */
22
23static 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
36static 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
54static 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
69static 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
79static 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}
102arch_initcall(sbf_init);
103