drm/i915: Fix reason for per-chip disabling of FBC

When running on my snb machine, recent kernels display successively:

[drm:intel_update_fbc], fbc set to per-chip default
[drm:intel_update_fbc], fbc disabled per module param

But no module param is set. This happens because the check for the
module parameter uses a variable that has been overridden inside the
"per-chip default" code.

Fix up the logic and add another reason for the FBC to the be disabled.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1518,6 +1518,9 @@ static int i915_fbc_status(struct seq_file *m, void *unused)
 		case FBC_MODULE_PARAM:
 			seq_printf(m, "disabled per module param (default off)");
 			break;
+		case FBC_CHIP_DEFAULT:
+			seq_printf(m, "disabled per chip default");
+			break;
 		default:
 			seq_printf(m, "unknown reason");
 		}

drivers/gpu/drm/i915/i915_drv.h

@@ -537,6 +537,7 @@ enum no_fbc_reason {
 	FBC_NOT_TILED, /* buffer not tiled */
 	FBC_MULTIPLE_PIPES, /* more than one pipe active */
 	FBC_MODULE_PARAM,
+	FBC_CHIP_DEFAULT, /* disabled by default on this chip */
 };
 
 enum intel_pch {

drivers/gpu/drm/i915/intel_pm.c

@@ -447,7 +447,6 @@ void intel_update_fbc(struct drm_device *dev)
 	struct drm_framebuffer *fb;
 	struct intel_framebuffer *intel_fb;
 	struct drm_i915_gem_object *obj;
-	int enable_fbc;
 	unsigned int max_hdisplay, max_vdisplay;
 
 	if (!i915_powersave)
@@ -488,14 +487,13 @@ void intel_update_fbc(struct drm_device *dev)
 	intel_fb = to_intel_framebuffer(fb);
 	obj = intel_fb->obj;
 
-	enable_fbc = i915_enable_fbc;
-	if (enable_fbc < 0) {
-		DRM_DEBUG_KMS("fbc set to per-chip default\n");
-		enable_fbc = 1;
-		if (INTEL_INFO(dev)->gen <= 7 && !IS_HASWELL(dev))
-			enable_fbc = 0;
+	if (i915_enable_fbc < 0 &&
+	    INTEL_INFO(dev)->gen <= 7 && !IS_HASWELL(dev)) {
+		DRM_DEBUG_KMS("disabled per chip default\n");
+		dev_priv->no_fbc_reason = FBC_CHIP_DEFAULT;
+		goto out_disable;
 	}
-	if (!enable_fbc) {
+	if (!i915_enable_fbc) {
 		DRM_DEBUG_KMS("fbc disabled per module param\n");
 		dev_priv->no_fbc_reason = FBC_MODULE_PARAM;
 		goto out_disable;