bootflag.c

 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);