drm/i915: Write the FDI RX TU size reg at the right time

According to "Graphics BSpec: vol4g North Display Engine Registers [IVB],
Display Mode Set Sequence" We need to write the TU size register
of the fdi RX unit _before_ starting to train the link.

Note: The current code is actually correct as Paulo mentioned in
review, but it's a bit confusion since only the fdi rx/tx plls need to
be enabled before the cpu pipes/planes. Hence it's still a good idea
to move the TU_SIZE setting to the "right" spot in the sequence, to
better match Bspec.
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2700,9 +2700,6 @@ static void ironlake_fdi_pll_enable(struct intel_crtc *intel_crtc)
 	int pipe = intel_crtc->pipe;
 	u32 reg, temp;
 
-	/* Write the TU size bits so error detection works */
-	I915_WRITE(FDI_RX_TUSIZE1(pipe),
-		   I915_READ(PIPE_DATA_M1(pipe)) & TU_SIZE_MASK);
 
 	/* enable PCH FDI RX PLL, wait warmup plus DMI latency */
 	reg = FDI_RX_CTL(pipe);
@@ -3003,6 +3000,11 @@ static void ironlake_pch_enable(struct drm_crtc *crtc)
 
 	assert_transcoder_disabled(dev_priv, pipe);
 
+	/* Write the TU size bits before fdi link training, so that error
+	 * detection works. */
+	I915_WRITE(FDI_RX_TUSIZE1(pipe),
+		   I915_READ(PIPE_DATA_M1(pipe)) & TU_SIZE_MASK);
+
 	/* For PCH output, training FDI link */
 	dev_priv->display.fdi_link_train(crtc);