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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 <linux/bitops.h>
12#include <asm/io.h>
13
14#include <linux/mc146818rtc.h>
15
16#define SBF_RESERVED (0x78)
17#define SBF_PNPOS (1<<0)
18#define SBF_BOOTING (1<<1)
19#define SBF_DIAG (1<<2)
20#define SBF_PARITY (1<<7)
21
22int sbf_port __initdata = -1; /* set via acpi_boot_init() */
23
24static void __init sbf_write(u8 v)
25{
26 unsigned long flags;
27
28 if (sbf_port != -1) {
29 if (!parity8(v))
30 v ^= SBF_PARITY;
31
32 printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n",
33 sbf_port, v);
34
35 spin_lock_irqsave(&rtc_lock, flags);
36 CMOS_WRITE(v, sbf_port);
37 spin_unlock_irqrestore(&rtc_lock, flags);
38 }
39}
40
41static u8 __init sbf_read(void)
42{
43 unsigned long flags;
44 u8 v;
45
46 if (sbf_port == -1)
47 return 0;
48
49 spin_lock_irqsave(&rtc_lock, flags);
50 v = CMOS_READ(sbf_port);
51 spin_unlock_irqrestore(&rtc_lock, flags);
52
53 return v;
54}
55
56static bool __init sbf_value_valid(u8 v)
57{
58 if (v & SBF_RESERVED) /* Reserved bits */
59 return false;
60 if (!parity8(v))
61 return false;
62
63 return true;
64}
65
66static int __init sbf_init(void)
67{
68 u8 v;
69
70 if (sbf_port == -1)
71 return 0;
72
73 v = sbf_read();
74 if (!sbf_value_valid(v)) {
75 printk(KERN_WARNING "Simple Boot Flag value 0x%x read from "
76 "CMOS RAM was invalid\n", v);
77 }
78
79 v &= ~SBF_RESERVED;
80 v &= ~SBF_BOOTING;
81 v &= ~SBF_DIAG;
82#if defined(CONFIG_ISAPNP)
83 v |= SBF_PNPOS;
84#endif
85 sbf_write(v);
86
87 return 0;
88}
89arch_initcall(sbf_init);