drm/i915: Provide a command line option to disable display

If we can't actually determine at run-time we have a fused-off display,
provide at least an option to disable it.

v2: Move the i915.disable_display test in a separate check
    (Daniel Vetter)

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/i915_dma.c b/drivers/gpu/drm/i915/i915_dma.c
index 033c943..1d65dbd 100644
--- a/drivers/gpu/drm/i915/i915_dma.c
+++ b/drivers/gpu/drm/i915/i915_dma.c
@@ -1483,9 +1483,12 @@
 	if (IS_VALLEYVIEW(dev))
 		info->num_sprites = 2;
 
-	if (info->num_pipes > 0 &&
-	    (INTEL_INFO(dev)->gen == 7 || INTEL_INFO(dev)->gen == 8) &&
-	    !IS_VALLEYVIEW(dev)) {
+	if (i915.disable_display) {
+		DRM_INFO("Display disabled (module parameter)\n");
+		info->num_pipes = 0;
+	} else if (info->num_pipes > 0 &&
+		   (INTEL_INFO(dev)->gen == 7 || INTEL_INFO(dev)->gen == 8) &&
+		   !IS_VALLEYVIEW(dev)) {
 		u32 fuse_strap = I915_READ(FUSE_STRAP);
 		u32 sfuse_strap = I915_READ(SFUSE_STRAP);