staging: vboxvideo: Keep old mode when disable crtc

On DPMS off we get a call to vbx_crtc_atomic_disable, followed by
a call to vbox_primary_atomic_update, at which point crtc_state->enable
is 0 and crtc_state->mode has been zero-ed. On a 0 width/height
vbox_do_modeset() falls back to 640x480, so this causes the guest Window
(its "monitor") to resize to 640x480 (and become black).

This commit makes us not look at crtc_state->mode when crtc_state->enable
is not set, so that we keep the old mode and just make the window go black.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vboxvideo/vbox_mode.c

@@ -190,7 +190,6 @@ static bool vbox_set_up_input_mapping(struct vbox_private *vbox)
 
 static void vbox_crtc_set_base_and_mode(struct drm_crtc *crtc,
 					struct drm_framebuffer *fb,
-					struct drm_display_mode *mode,
 					int x, int y)
 {
 	struct vbox_bo *bo = gem_to_vbox_bo(to_vbox_framebuffer(fb)->obj);
@@ -200,8 +199,11 @@ static void vbox_crtc_set_base_and_mode(struct drm_crtc *crtc,
 
 	mutex_lock(&vbox->hw_mutex);
 
-	vbox_crtc->width = mode->hdisplay;
-	vbox_crtc->height = mode->vdisplay;
+	if (crtc->state->enable) {
+		vbox_crtc->width = crtc->state->mode.hdisplay;
+		vbox_crtc->height = crtc->state->mode.vdisplay;
+	}
+
 	vbox_crtc->x = x;
 	vbox_crtc->y = y;
 	vbox_crtc->fb_offset = vbox_bo_gpu_offset(bo);
@@ -301,7 +303,7 @@ static void vbox_primary_atomic_update(struct drm_plane *plane,
 	struct drm_crtc *crtc = plane->state->crtc;
 	struct drm_framebuffer *fb = plane->state->fb;
 
-	vbox_crtc_set_base_and_mode(crtc, fb, &crtc->state->mode,
+	vbox_crtc_set_base_and_mode(crtc, fb,
 				    plane->state->src_x >> 16,
 				    plane->state->src_y >> 16);
 }
@@ -312,7 +314,7 @@ static void vbox_primary_atomic_disable(struct drm_plane *plane,
 	struct drm_crtc *crtc = old_state->crtc;
 
 	/* vbox_do_modeset checks plane->state->fb and will disable if NULL */
-	vbox_crtc_set_base_and_mode(crtc, old_state->fb, &crtc->state->mode,
+	vbox_crtc_set_base_and_mode(crtc, old_state->fb,
 				    old_state->src_x >> 16,
 				    old_state->src_y >> 16);
 }