drm/i915: fixup the plane->pipe fixup code

We need to check whether the _other plane is on our pipe, not whether
our plane is on the other pipe. Otherwise if not both pipes/planes are
active, we won't properly clean up the mess and set up our desired
plane->pipe mapping.

v2: Fixup the logic, I've totally fumbled it. Noticed by Chris Wilson.

v3: I've checked Bspec, and the flexible plane->pipe mapping is a
gen2/3 feature, so test for that instead of PCH_SPLIT

v4: Check whether we indeed have 2 pipes before checking the other
pipe, to avoid upsetting i845g/i865g. Noticed by Chris Wilson.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51265
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=49838
Tested-by: Dave Airlie <airlied@gmail.com>
Tested-by: Chris Wilson <chris@chris-wilson.co.uk> #855gm
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -8058,29 +8058,42 @@ static void intel_enable_pipe_a(struct drm_device *dev)
 
 }
 
+static bool
+intel_check_plane_mapping(struct intel_crtc *crtc)
+{
+	struct drm_i915_private *dev_priv = crtc->base.dev->dev_private;
+	u32 reg, val;
+
+	if (dev_priv->num_pipe == 1)
+		return true;
+
+	reg = DSPCNTR(!crtc->plane);
+	val = I915_READ(reg);
+
+	if ((val & DISPLAY_PLANE_ENABLE) &&
+	    (!!(val & DISPPLANE_SEL_PIPE_MASK) == crtc->pipe))
+		return false;
+
+	return true;
+}
+
 static void intel_sanitize_crtc(struct intel_crtc *crtc)
 {
 	struct drm_device *dev = crtc->base.dev;
 	struct drm_i915_private *dev_priv = dev->dev_private;
-	u32 reg, val;
+	u32 reg;
 
 	/* Clear any frame start delays used for debugging left by the BIOS */
 	reg = PIPECONF(crtc->pipe);
 	I915_WRITE(reg, I915_READ(reg) & ~PIPECONF_FRAME_START_DELAY_MASK);
 
 	/* We need to sanitize the plane -> pipe mapping first because this will
-	 * disable the crtc (and hence change the state) if it is wrong. */
-	if (!HAS_PCH_SPLIT(dev)) {
+	 * disable the crtc (and hence change the state) if it is wrong. Note
+	 * that gen4+ has a fixed plane -> pipe mapping.  */
+	if (INTEL_INFO(dev)->gen < 4 && !intel_check_plane_mapping(crtc)) {
 		struct intel_connector *connector;
 		bool plane;
 
-		reg = DSPCNTR(crtc->plane);
-		val = I915_READ(reg);
-
-		if ((val & DISPLAY_PLANE_ENABLE) == 0 &&
-		    (!!(val & DISPPLANE_SEL_PIPE_MASK) == crtc->pipe))
-			goto ok;
-
 		DRM_DEBUG_KMS("[CRTC:%d] wrong plane connection detected!\n",
 			      crtc->base.base.id);
 
@@ -8104,7 +8117,6 @@ static void intel_sanitize_crtc(struct intel_crtc *crtc)
 		WARN_ON(crtc->active);
 		crtc->base.enabled = false;
 	}
-ok:
 
 	if (dev_priv->quirks & QUIRK_PIPEA_FORCE &&
 	    crtc->pipe == PIPE_A && !crtc->active) {