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