x86/virt, x86/acpi: Add test for ACPI_FADT_NO_VGA

Add a test for ACPI_FADT_NO_VGA when scanning the FADT and set the new
flag x86_platform.legacy.no_vga accordingly.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: len.brown@intel.com
Cc: linux-pm@vger.kernel.org
Cc: pavel@ucw.cz
Cc: rjw@rjwysocki.net
Link: http://lkml.kernel.org/r/20171109132739.23465-4-jgross@suse.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/x86_init.h

@@ -208,6 +208,7 @@ enum x86_legacy_i8042_state {
 struct x86_legacy_features {
 	enum x86_legacy_i8042_state i8042;
 	int rtc;
+	int no_vga;
 	int reserve_bios_regions;
 	struct x86_legacy_devices devices;
 };

arch/x86/kernel/acpi/boot.c

@@ -961,6 +961,11 @@ static int __init acpi_parse_fadt(struct acpi_table_header *table)
 		x86_platform.legacy.rtc = 0;
 	}
 
+	if (acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_VGA) {
+		pr_debug("ACPI: probing for VGA not safe\n");
+		x86_platform.legacy.no_vga = 1;
+	}
+
 #ifdef CONFIG_X86_PM_TIMER
 	/* detect the location of the ACPI PM Timer */
 	if (acpi_gbl_FADT.header.revision >= FADT2_REVISION_ID) {