From c2272faa06dec2f027c5359529cf8f4f3593c164 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roger=20Pau=20Monn=C3=A9?= <royger@FreeBSD.org>
Date: Tue, 13 Mar 2018 09:38:53 +0000
Subject: [PATCH] vt_vga: check if VGA is available from ACPI FADT table

On x86 the IA-PC Boot Flags in the FADT can signal whether VGA is
available or not.

Sponsored by:		Citrix systems R&D
Reviewed by:		marcel
Differential revision:	https://reviews.freebsd.org/D14397
---
 sys/dev/vt/hw/vga/vt_vga.c | 36 +++++++++++++++++++++++++++++++++++-
 1 file changed, 35 insertions(+), 1 deletion(-)

diff --git a/sys/dev/vt/hw/vga/vt_vga.c b/sys/dev/vt/hw/vga/vt_vga.c
index 502aaca3377..820b6426244 100644
--- a/sys/dev/vt/hw/vga/vt_vga.c
+++ b/sys/dev/vt/hw/vga/vt_vga.c
@@ -30,6 +30,8 @@
  * SUCH DAMAGE.
  */
 
+#include "opt_acpi.h"
+
 #include <sys/cdefs.h>
 __FBSDID("$FreeBSD$");
 
@@ -46,6 +48,10 @@ __FBSDID("$FreeBSD$");
 
 #include <machine/bus.h>
 
+#if ((defined(__amd64__) || defined(__i386__)) && defined(DEV_ACPI))
+#include <contrib/dev/acpica/include/acpi.h>
+#endif
+
 struct vga_softc {
 	bus_space_tag_t		 vga_fb_tag;
 	bus_space_handle_t	 vga_fb_handle;
@@ -1196,11 +1202,39 @@ vga_initialize(struct vt_device *vd, int textmode)
 	return (0);
 }
 
+static bool
+vga_acpi_disabled(void)
+{
+#if ((defined(__amd64__) || defined(__i386__)) && defined(DEV_ACPI))
+	ACPI_TABLE_FADT *fadt;
+	vm_paddr_t physaddr;
+	uint16_t flags;
+
+	physaddr = acpi_find_table(ACPI_SIG_FADT);
+	if (physaddr == 0)
+		return (false);
+
+	fadt = acpi_map_table(physaddr, ACPI_SIG_FADT);
+	if (fadt == NULL) {
+		printf("vt_vga: unable to map FADT ACPI table\n");
+		return (false);
+	}
+
+	flags = fadt->BootFlags;
+	acpi_unmap_table(fadt);
+
+	if (flags & ACPI_FADT_NO_VGA)
+		return (true);
+#endif
+
+	return (false);
+}
+
 static int
 vga_probe(struct vt_device *vd)
 {
 
-	return (CN_INTERNAL);
+	return (vga_acpi_disabled() ? CN_DEAD : CN_INTERNAL);
 }
 
 static int