+static void intel_sanitize_modesetting(struct drm_device *dev,
+ int pipe, int plane)
+{
+ struct drm_i915_private *dev_priv = dev->dev_private;
+ u32 reg, val;
+
+ if (HAS_PCH_SPLIT(dev))
+ return;
+
+ /* Who knows what state these registers were left in by the BIOS or
+ * grub?
+ *
+ * If we leave the registers in a conflicting state (e.g. with the
+ * display plane reading from the other pipe than the one we intend
+ * to use) then when we attempt to teardown the active mode, we will
+ * not disable the pipes and planes in the correct order -- leaving
+ * a plane reading from a disabled pipe and possibly leading to
+ * undefined behaviour.
+ */
+
+ reg = DSPCNTR(plane);
+ val = I915_READ(reg);
+
+ if ((val & DISPLAY_PLANE_ENABLE) == 0)
+ return;
+ if (!!(val & DISPPLANE_SEL_PIPE_MASK) == pipe)
+ return;
+
+ /* This display plane is active and attached to the other CPU pipe. */
+ pipe = !pipe;
+
+ /* Disable the plane and wait for it to stop reading from the pipe. */
+ I915_WRITE(reg, val & ~DISPLAY_PLANE_ENABLE);
+ intel_flush_display_plane(dev, plane);
+
+ if (IS_GEN2(dev))
+ intel_wait_for_vblank(dev, pipe);
+
+ if (pipe == 0 && (dev_priv->quirks & QUIRK_PIPEA_FORCE))
+ return;
+
+ /* Switch off the pipe. */
+ reg = PIPECONF(pipe);
+ val = I915_READ(reg);
+ if (val & PIPECONF_ENABLE) {
+ I915_WRITE(reg, val & ~PIPECONF_ENABLE);
+ intel_wait_for_pipe_off(dev, pipe);
+ }
+}