xref: /openbmc/linux/arch/x86/kernel/bootflag.c (revision b2441318)
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 
parity(u8 v)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 
sbf_write(u8 v)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(&rtc_lock, flags);
51 	}
52 }
53 
sbf_read(void)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(&rtc_lock, flags);
65 
66 	return v;
67 }
68 
sbf_value_valid(u8 v)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 
sbf_init(void)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