drm/i915: Do not enable FEC without DSC

Currently we enable FEC even when DSC is no used. While that is
theoretically valid supposedly there isn't much of a benefit from
this. But more importantly we do not account for the FEC link
bandwidth overhead (2.4%) in the non-DSC link bandwidth computations.
So the code may think we have enough bandwidth when we in fact
do not.

Cc: stable@vger.kernel.org
Cc: Anusha Srivatsa <anusha.srivatsa@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Fixes: 240999cf ("i915/dp/fec: Add fec_enable to the crtc state.")
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190326144903.6617-1-ville.syrjala@linux.intel.comReviewed-by: Manasi Navare <manasi.d.navare@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -1895,6 +1895,9 @@ static int intel_dp_dsc_compute_config(struct intel_dp *intel_dp,
 	int pipe_bpp;
 	int ret;
 
+	pipe_config->fec_enable = !intel_dp_is_edp(intel_dp) &&
+		intel_dp_supports_fec(intel_dp, pipe_config);
+
 	if (!intel_dp_supports_dsc(intel_dp, pipe_config))
 		return -EINVAL;
 
@@ -2156,9 +2159,6 @@ intel_dp_compute_config(struct intel_encoder *encoder,
 	if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
 		return -EINVAL;
 
-	pipe_config->fec_enable = !intel_dp_is_edp(intel_dp) &&
-				  intel_dp_supports_fec(intel_dp, pipe_config);
-
 	ret = intel_dp_compute_link_config(encoder, pipe_config, conn_state);
 	if (ret < 0)
 		return ret;