drm/i915: Fix eDP low vswing for Broadwell

commit 992e7a41 upstream.

It was noticed on bug #94087 that module parameter
i915.edp_vswing=2 that should override the VBT setting
to use default voltage swing (400 mV) was not applied
for Broadwell.

This patch provides a fix for this by checking if default
i.e. higher voltage swing is requested to be used and
applies the DDI translations table for DP instead of eDP
(low vswing) table.

v2: Combine two if statements into one (Jani)
v3: Change dev_priv->edp_low_vswing to use dev_priv->vbt.edp.low_vswing

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94087Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461155942-7749-1-git-send-email-mika.kahola@intel.comSigned-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
(cherry picked from commit 00983519)
[Jani: s/dev_priv->vbt.edp.low_vswing/dev_priv->edp_low_vswing/ to backport]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/gpu/drm/i915/intel_ddi.c

@@ -296,9 +296,17 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port,
 	} else if (IS_BROADWELL(dev)) {
 		ddi_translations_fdi = bdw_ddi_translations_fdi;
 		ddi_translations_dp = bdw_ddi_translations_dp;
-		ddi_translations_edp = bdw_ddi_translations_edp;
+
+		if (dev_priv->edp_low_vswing) {
+			ddi_translations_edp = bdw_ddi_translations_edp;
+			n_edp_entries = ARRAY_SIZE(bdw_ddi_translations_edp);
+		} else {
+			ddi_translations_edp = bdw_ddi_translations_dp;
+			n_edp_entries = ARRAY_SIZE(bdw_ddi_translations_dp);
+		}
+
 		ddi_translations_hdmi = bdw_ddi_translations_hdmi;
-		n_edp_entries = ARRAY_SIZE(bdw_ddi_translations_edp);
+
 		n_dp_entries = ARRAY_SIZE(bdw_ddi_translations_dp);
 		n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi);
 		hdmi_default_entry = 7;