1 files changed, 86 insertions, 0 deletions
diff --git a/arch/x86/boot/prepare_uboot.c b/arch/x86/boot/prepare_uboot.c
new file mode 100644
index 0000000000..a68aceddb6
--- /dev/null
+++ b/arch/x86/boot/prepare_uboot.c
@@ -0,0 +1,86 @@
+/* -*- linux-c -*- ------------------------------------------------------- *
+ *
+ *   Copyright (C) 1991, 1992 Linus Torvalds
+ *   Copyright 2007 rPath, Inc. - All Rights Reserved
+ *
+ *   This file is part of the Linux kernel, and is made available under
+ *   the terms of the GNU General Public License version 2.
+ *
+ * ----------------------------------------------------------------------- */
+
+/*
+ * Prepare the machine for transition to protected mode.
+ */
+#include <asm/segment.h>
+#include <asm/modes.h>
+#include <asm/io.h>
+#include "boot.h"
+
+/* be aware of: */
+THIS_IS_REALMODE_CODE
+
+/*
+ * While we are in flat mode, we can't handle interrupts. But we can't
+ * switch them off for ever in the PIC, because we need them again while
+ * entering real mode code again and again....
+ */
+static void __bootcode realmode_switch_hook(void)
+{
+	asm volatile("cli");
+	outb(0x80, 0x70); /* Disable NMI */
+	io_delay();
+}
+
+/*
+ * Reset IGNNE# if asserted in the FPU.
+ */
+static void __bootcode reset_coprocessor(void)
+{
+	outb(0, 0xf0);
+	io_delay();
+	outb(0, 0xf1);
+	io_delay();
+}
+
+/**
+ * Setup and register the global descriptor table (GDT)
+ *
+ * @note This is for the first time only
+ */
+static void __bootcode setup_gdt(void)
+{
+	/* Xen HVM incorrectly stores a pointer to the gdt_ptr, instead
+	   of the gdt_ptr contents.  Thus, make it static so it will
+	   stay in memory, at least long enough that we switch to the
+	   proper kernel GDT. */
+	static struct gdt_ptr __bootdata gdt_ptr;
+
+	gdt_ptr.len = gdt_size - 1;
+	gdt_ptr.ptr = (uint32_t)&gdt + (ds() << 4);
+
+	asm volatile("lgdtl %0" : : "m" (gdt_ptr));
+}
+
+static char a20_message[] __bootdata = "A20 gate not responding, unable to boot...\n";
+
+/*
+ * Actual invocation sequence
+ */
+void __bootcode start_pre_uboot(void)
+{
+	/* Hook before leaving real mode, also disables interrupts */
+	realmode_switch_hook();
+
+	/* Enable the A20 gate */
+	if (enable_a20()) {
+		boot_puts(a20_message);
+		die();
+	}
+
+	/* Reset coprocessor (IGNNE#) */
+	reset_coprocessor();
+
+	setup_gdt();
+	/* Actual transition to protected mode... */
+	protected_mode_jump();
+}