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authorH. Peter Anvin <hpa@zytor.com>2008-07-14 11:44:26 -0700
committerH. Peter Anvin <hpa@zytor.com>2008-07-14 11:44:26 -0700
commit065cb3dfe24978651caedfa54da585388ad15dde (patch)
tree692de26e80c86faa4e0bd6831e7180ff6ec5af6c /arch/x86/kernel/acpi
parent3bf2e77453a87c22eb57ed4926760ac131c84459 (diff)
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: H. Peter Anvin <hpa@zytor.com>
Diffstat (limited to 'arch/x86/kernel/acpi')
-rw-r--r--arch/x86/kernel/acpi/sleep.c13
1 files changed, 11 insertions, 2 deletions
diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 130711f1454..41bb130c31d 100644
--- a/arch/x86/kernel/acpi/sleep.c
+++ b/arch/x86/kernel/acpi/sleep.c
@@ -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);