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// SPDX-License-Identifier: GPL-2.0
/*
* Implement 'Simple Boot Flag Specification 2.0'
*/
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/spinlock.h>
#include <linux/acpi.h>
#include <asm/io.h>
#include <linux/mc146818rtc.h>
#define SBF_RESERVED (0x78)
#define SBF_PNPOS (1<<0)
#define SBF_BOOTING (1<<1)
#define SBF_DIAG (1<<2)
#define SBF_PARITY (1<<7)
int sbf_port __initdata = -1; /* set via acpi_boot_init() */
static int __init parity(u8 v)
{
int x = 0;
int i;
for (i = 0; i < 8; i++) {
x ^= (v & 1);
v >>= 1;
}
return x;
}
static void __init sbf_write(u8 v)
{
unsigned long flags;
if (sbf_port != -1) {
v &= ~SBF_PARITY;
if (!parity(v))
v |= SBF_PARITY;
printk(KERN_INFO "Simple Boot Flag at 0x%x set to 0x%x\n",
sbf_port, v);
spin_lock_irqsave(&rtc_lock, flags);
CMOS_WRITE(v, sbf_port);
spin_unlock_irqrestore(&rtc_lock, flags);
}
}
static u8 __init sbf_read(void)
{
unsigned long flags;
u8 v;
if (sbf_port == -1)
return 0;
spin_lock_irqsave(&rtc_lock, flags);
v = CMOS_READ(sbf_port);
spin_unlock_irqrestore(&rtc_lock, flags);
return v;
}
static int __init sbf_value_valid(u8 v)
{
if (v & SBF_RESERVED) /* Reserved bits */
return 0;
if (!parity(v))
return 0;
return 1;
}
static int __init sbf_init(void)
{
u8 v;
if (sbf_port == -1)
return 0;
v = sbf_read();
if (!sbf_value_valid(v)) {
printk(KERN_WARNING "Simple Boot Flag value 0x%x read from "
"CMOS RAM was invalid\n", v);
}
v &= ~SBF_RESERVED;
v &= ~SBF_BOOTING;
v &= ~SBF_DIAG;
#if defined(CONFIG_ISAPNP)
v |= SBF_PNPOS;
#endif
sbf_write(v);
return 0;
}
arch_initcall(sbf_init);
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