drm/i915/gen9+: Fix initial readout for Y tiled framebuffers

If BIOS configured a Y tiled FB we failed to set up the backing object
tiling accordingly, leading to a lack of GT fence installed and a
garbled console.

The problem was bisected to
commit 011f22eb ("drm/i915: Do NOT skip the first 4k of stolen memory for pre-allocated buffers v2")
but it just revealed a pre-existing issue.

Kudos to Ville who suspected a missing fence looking at the corruption
on the screen.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: <ronald@innovation.ch>
Cc: <stable@vger.kernel.org>
Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reported-by: <ronald@innovation.ch>
Tested-by: <ronald@innovation.ch>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108264
Fixes: bc8d7dff ("drm/i915/skl: Provide a Skylake version of get_plane_config()")
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181016160011.28347-1-imre.deak@intel.com

drivers/gpu/drm/i915/intel_display.c

@@ -2673,6 +2673,17 @@ intel_alloc_initial_plane_obj(struct intel_crtc *crtc,
 	if (size_aligned * 2 > dev_priv->stolen_usable_size)
 		return false;
 
+	switch (fb->modifier) {
+	case DRM_FORMAT_MOD_LINEAR:
+	case I915_FORMAT_MOD_X_TILED:
+	case I915_FORMAT_MOD_Y_TILED:
+		break;
+	default:
+		DRM_DEBUG_DRIVER("Unsupported modifier for initial FB: 0x%llx\n",
+				 fb->modifier);
+		return false;
+	}
+
 	mutex_lock(&dev->struct_mutex);
 	obj = i915_gem_object_create_stolen_for_preallocated(dev_priv,
 							     base_aligned,
@@ -2682,8 +2693,17 @@ intel_alloc_initial_plane_obj(struct intel_crtc *crtc,
 	if (!obj)
 		return false;
 
-	if (plane_config->tiling == I915_TILING_X)
-		obj->tiling_and_stride = fb->pitches[0] | I915_TILING_X;
+	switch (plane_config->tiling) {
+	case I915_TILING_NONE:
+		break;
+	case I915_TILING_X:
+	case I915_TILING_Y:
+		obj->tiling_and_stride = fb->pitches[0] | plane_config->tiling;
+		break;
+	default:
+		MISSING_CASE(plane_config->tiling);
+		return false;
+	}
 
 	mode_cmd.pixel_format = fb->format->format;
 	mode_cmd.width = fb->width;
@@ -8837,6 +8857,7 @@ skylake_get_initial_plane_config(struct intel_crtc *crtc,
 		fb->modifier = I915_FORMAT_MOD_X_TILED;
 		break;
 	case PLANE_CTL_TILED_Y:
+		plane_config->tiling = I915_TILING_Y;
 		if (val & PLANE_CTL_RENDER_DECOMPRESSION_ENABLE)
 			fb->modifier = I915_FORMAT_MOD_Y_TILED_CCS;
 		else