drm/i915: correct intel_dp_get_config() function for DevCPT

On DevCPT, the control register for Transcoder DP Sync Polarity is
TRANS_DP_CTL, not DP_CTL.
Without this patch, Many call trace occur on CPT machine with DP monitor.
The call trace is like: *ERROR* mismatch in adjusted_mode.flags(expected X,found X)

v2: use intel-crtc to simple patch, suggested by Daniel.

Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>
[danvet: Extend the encoder->get_config comment to specify that we now
also depend upon intel_encoder->base.crtc being correct. Also bikeshed
s/intel_crtc/crtc/.]
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=65287
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_dp.c

@@ -1324,20 +1324,35 @@ static void intel_dp_get_config(struct intel_encoder *encoder,
 				struct intel_crtc_config *pipe_config)
 {
 	struct intel_dp *intel_dp = enc_to_intel_dp(&encoder->base);
-	struct drm_i915_private *dev_priv = encoder->base.dev->dev_private;
 	u32 tmp, flags = 0;
+	struct drm_device *dev = encoder->base.dev;
+	struct drm_i915_private *dev_priv = dev->dev_private;
+	enum port port = dp_to_dig_port(intel_dp)->port;
+	struct intel_crtc *crtc = to_intel_crtc(encoder->base.crtc);
 
-	tmp = I915_READ(intel_dp->output_reg);
+	if ((port == PORT_A) || !HAS_PCH_CPT(dev)) {
+		tmp = I915_READ(intel_dp->output_reg);
+		if (tmp & DP_SYNC_HS_HIGH)
+			flags |= DRM_MODE_FLAG_PHSYNC;
+		else
+			flags |= DRM_MODE_FLAG_NHSYNC;
 
-	if (tmp & DP_SYNC_HS_HIGH)
-		flags |= DRM_MODE_FLAG_PHSYNC;
-	else
-		flags |= DRM_MODE_FLAG_NHSYNC;
+		if (tmp & DP_SYNC_VS_HIGH)
+			flags |= DRM_MODE_FLAG_PVSYNC;
+		else
+			flags |= DRM_MODE_FLAG_NVSYNC;
+	} else {
+		tmp = I915_READ(TRANS_DP_CTL(crtc->pipe));
+		if (tmp & TRANS_DP_HSYNC_ACTIVE_HIGH)
+			flags |= DRM_MODE_FLAG_PHSYNC;
+		else
+			flags |= DRM_MODE_FLAG_NHSYNC;
 
-	if (tmp & DP_SYNC_VS_HIGH)
-		flags |= DRM_MODE_FLAG_PVSYNC;
-	else
-		flags |= DRM_MODE_FLAG_NVSYNC;
+		if (tmp & TRANS_DP_VSYNC_ACTIVE_HIGH)
+			flags |= DRM_MODE_FLAG_PVSYNC;
+		else
+			flags |= DRM_MODE_FLAG_NVSYNC;
+	}
 
 	pipe_config->adjusted_mode.flags |= flags;
 }

drivers/gpu/drm/i915/intel_drv.h

@@ -141,7 +141,8 @@ struct intel_encoder {
 	bool (*get_hw_state)(struct intel_encoder *, enum pipe *pipe);
 	/* Reconstructs the equivalent mode flags for the current hardware
 	 * state. This must be called _after_ display->get_pipe_config has
-	 * pre-filled the pipe config. */
+	 * pre-filled the pipe config. Note that intel_encoder->base.crtc must
+	 * be set correctly before calling this function. */
 	void (*get_config)(struct intel_encoder *,
 			   struct intel_crtc_config *pipe_config);
 	int crtc_mask;