realmode/rm/reboot.S

1 /* SPDX-License-Identifier: GPL-2.0 */
6 #include <asm/processor-flags.h>
7 #include <asm/msr-index.h>
14  * controller to pulse the CPU reset line, which is more thorough, but
15  * doesn't work with at least one type of 486 motherboard.  It is easy
18  * This code is called with the restart type (0 = BIOS, 1 = APM) in
26 	/* Switch to trampoline GDT as it is guaranteed < 4 GiB */
52 	 * mode.  The GDT is not used in real mode; it is just needed here to
58 	 * Load the data segment registers with 16-bit compatible values
70  * This is 16-bit protected mode code to disable paging and the cache,
74  * followed immediately by a far jump instruction, which set CS to a
76  * running instructions that have already been decoded in protected
80  * (protected-mode enable) and TS (task switch for coprocessor state
83  * is more like the state of a 486 after reset.  I don't know if
87  * occurred; hopefully real BIOSs don't assume much.  This is not the
88  * actual BIOS entry point, anyway (that is at 0xfffffff0).
90  * Most of this work is probably excessive, but it is what is tested.
105 	testl	$0x60000000, %edx	/* If no cache bits -> no wbinvd */
133 	.word	0xffff		/* Length - real mode default value */
134 	.long	0		/* Base - real mode default value */
139 	/* Self-pointer */
140 	.word	0xffff		/* Length - real mode default value */
145 	 * 16-bit code segment pointing to real_mode_seg
153 	 * 16-bit data segment with the selector value 16 = 0x10 and
154 	 * base value 0x100; since this is consistent with real mode