drm/nouveau/kms: Avoid a hang entering KDB with VT accel on.

Francisco Jerez advises that pre-nv20 cards would hang if we entered
kdb with accel on and IRQs disabled, so we now disable accel before
entering kdb and re-enable it on the way back out.
Reported-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Chris Ball <cjb@laptop.org>
Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/nouveau/nv04_crtc.c

@@ -33,6 +33,7 @@
 #include "nouveau_fb.h"
 #include "nouveau_hw.h"
 #include "nvreg.h"
+#include "nouveau_fbcon.h"
 
 static int
 nv04_crtc_mode_set_base(struct drm_crtc *crtc, int x, int y,
@@ -860,6 +861,14 @@ nv04_crtc_mode_set_base_atomic(struct drm_crtc *crtc,
 			       struct drm_framebuffer *fb,
 			       int x, int y, int enter)
 {
+	struct drm_nouveau_private *dev_priv = crtc->dev->dev_private;
+	struct drm_device *dev = dev_priv->dev;
+
+	if (enter)
+		nouveau_fbcon_save_disable_accel(dev);
+	else
+		nouveau_fbcon_restore_accel(dev);
+
 	return nv04_crtc_do_mode_set_base(crtc, fb, x, y, true);
 }