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

[linux-2.6-omap-h63xx.git] / arch / x86 / kernel / acpi / sleep.c

diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
index 130711f1454b9ee5a179cf201abbf17b8d54d439..41bb130c31db84d003d504d1a89bbab56a15c4e0 100644 (file)
--- 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);