1 files changed, 102 insertions, 0 deletions
diff --git a/arch/x86/kernel/bootflag.c b/arch/x86/kernel/bootflag.c
new file mode 100644
index 0000000000..3fed7ae58b
--- /dev/null
+++ b/arch/x86/kernel/bootflag.c
@@ -0,0 +1,102 @@
+// 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);