drm/i915: disable sdvo pixel multiplier cross-check for HAS_PCH_SPLIT

We don't (yet) have proper pixel multiplier readout support on pch
split platforms, so the cross check will naturally fail.

v2: Fix spelling in the comment, spotted by Ville.

v3: Since the ordering constraint is pretty tricky between the crtc
get_pipe_config callback and the encoder->get_config callback add a
few comments about it. Prompted by a discussion with Chris Wilson on
irc about why this does work anywhere else than on i915g/gm.

Reported-by: Chris Wilson <chris@chris-wilson.co.uk>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_drv.h

@@ -140,7 +140,8 @@ struct intel_encoder {
 	 * it is connected to in the pipe parameter. */
 	bool (*get_hw_state)(struct intel_encoder *, enum pipe *pipe);
 	/* Reconstructs the equivalent mode flags for the current hardware
-	 * state. */
+	 * state. This must be called _after_ display->get_pipe_config has
+	 * pre-filled the pipe config. */
 	void (*get_config)(struct intel_encoder *,
 			   struct intel_crtc_config *pipe_config);
 	int crtc_mask;

drivers/gpu/drm/i915/intel_sdvo.c

@@ -1342,6 +1342,13 @@ static void intel_sdvo_get_config(struct intel_encoder *encoder,
 
 	pipe_config->adjusted_mode.flags |= flags;
 
+	/*
+	 * pixel multiplier readout is tricky: Only on i915g/gm it is stored in
+	 * the sdvo port register, on all other platforms it is part of the dpll
+	 * state. Since the general pipe state readout happens before the
+	 * encoder->get_config we so already have a valid pixel multplier on all
+	 * other platfroms.
+	 */
 	if (IS_I915G(dev) || IS_I915GM(dev)) {
 		sdvox = I915_READ(intel_sdvo->sdvo_reg);
 		pipe_config->pixel_multiplier =
@@ -1362,6 +1369,10 @@ static void intel_sdvo_get_config(struct intel_encoder *encoder,
 		encoder_pixel_multiplier = 4;
 		break;
 	}
+
+	if(HAS_PCH_SPLIT(dev))
+		return; /* no pixel multiplier readout support yet */
+
 	WARN(encoder_pixel_multiplier != pipe_config->pixel_multiplier,
 	     "SDVO pixel multiplier mismatch, port: %i, encoder: %i\n",
 	     pipe_config->pixel_multiplier, encoder_pixel_multiplier);