drm/i915/fbc: Introduce intel_fbc_sanitize()

Let's make sure FBC is always disabled when we start to take
over the hardware state.

I suspect this should never really happen, since the only time
when we really should be taking over with the display already
active is when the previous state was progammed by the BIOS,
which likely shouldn't use FBC. This could be driver init,
or S4 resume when the boot kernel doesn't load i915. But I
suppose no harm in keeping this code around for exra safety
since it's quite trivial.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220315140001.1172-7-ville.syrjala@linux.intel.comReviewed-by: Mika Kahola <mika.kahola@intel.com>

drivers/gpu/drm/i915/display/intel_display.c

@@ -10430,6 +10430,8 @@ intel_modeset_setup_hw_state(struct drm_device *dev,
 			intel_crtc_vblank_on(crtc_state);
 	}
 
+	intel_fbc_sanitize(dev_priv);
+
 	intel_sanitize_plane_mapping(dev_priv);
 
 	for_each_intel_encoder(dev, encoder)

drivers/gpu/drm/i915/display/intel_fbc.c

@@ -1703,22 +1703,26 @@ void intel_fbc_init(struct drm_i915_private *i915)
 	drm_dbg_kms(&i915->drm, "Sanitized enable_fbc value: %d\n",
 		    i915->params.enable_fbc);
 
-	for_each_fbc_id(i915, fbc_id) {
-		struct intel_fbc *fbc;
+	for_each_fbc_id(i915, fbc_id)
+		i915->fbc[fbc_id] = intel_fbc_create(i915, fbc_id);
+}
 
-		fbc = intel_fbc_create(i915, fbc_id);
-		if (!fbc)
-			continue;
+/**
+ * intel_fbc_sanitize - Sanitize FBC
+ * @i915: the i915 device
+ *
+ * Make sure FBC is initially disabled since we have no
+ * idea eg. into which parts of stolen it might be scribbling
+ * into.
+ */
+void intel_fbc_sanitize(struct drm_i915_private *i915)
+{
+	struct intel_fbc *fbc;
+	enum intel_fbc_id fbc_id;
 
-		/*
-		 * We still don't have any sort of hardware state readout
-		 * for FBC, so deactivate it in case the BIOS activated it
-		 * to make sure software matches the hardware state.
-		 */
+	for_each_intel_fbc(i915, fbc, fbc_id) {
 		if (intel_fbc_hw_is_active(fbc))
 			intel_fbc_hw_deactivate(fbc);
-
-		i915->fbc[fbc->id] = fbc;
 	}
 }
 

drivers/gpu/drm/i915/display/intel_fbc.h

@@ -30,6 +30,7 @@ void intel_fbc_post_update(struct intel_atomic_state *state,
 			   struct intel_crtc *crtc);
 void intel_fbc_init(struct drm_i915_private *dev_priv);
 void intel_fbc_cleanup(struct drm_i915_private *dev_priv);
+void intel_fbc_sanitize(struct drm_i915_private *dev_priv);
 void intel_fbc_update(struct intel_atomic_state *state,
 		      struct intel_crtc *crtc);
 void intel_fbc_disable(struct intel_crtc *crtc);