Commit 065cb3df authored by H. Peter Anvin's avatar H. Peter Anvin
Browse files

x86, suspend, acpi: correct and add comments about Big Real Mode 



Explain that we set up the descriptors for Big Real Mode, and why we
do so.  In particular, one system that is known to fail without it is
the Lenovo X61.

Signed-off-by: default avatarH. Peter Anvin <hpa@zytor.com>
parent 3bf2e774

arch/x86/kernel/acpi/sleep.c

+11 −2
Original line number Diff line number Diff line
@@ -60,16 +60,25 @@ int acpi_save_state_mem(void) 
	header->video_mode = saved_video_mode;



	header->wakeup_jmp_seg = acpi_wakeup_address >> 4;



	/*

	 * Set up the wakeup GDT.  We set these up as Big Real Mode,

	 * that is, with limits set to 4 GB.  At least the Lenovo

	 * Thinkpad X61 is known to need this for the video BIOS

	 * initialization quirk to work; this is likely to also

	 * be the case for other laptops or integrated video devices.

	 */



	/* GDT[0]: GDT self-pointer */

	header->wakeup_gdt[0] =

		(u64)(sizeof(header->wakeup_gdt) - 1) +

		((u64)(acpi_wakeup_address +

			((char *)&header->wakeup_gdt - (char *)acpi_realmode))

				<< 16);

	/* GDT[1]: real-mode-like code segment */

	/* GDT[1]: big real mode-like code segment */

	header->wakeup_gdt[1] =

		GDT_ENTRY(0x809b, acpi_wakeup_address, 0xfffff);

	/* GDT[2]: real-mode-like data segment */

	/* GDT[2]: big real mode-like data segment */

	header->wakeup_gdt[2] =

		GDT_ENTRY(0x8093, acpi_wakeup_address, 0xfffff);

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