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(lock: &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(lock: &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); |
103 |