drm/i915: Fix eDP low vswing for Broadwell

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=94087
Signed-off-by: Mika Kahola <mika.kahola@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1461155942-7749-1-git-send-email-mika.kahola@intel.com
Cc: stable@vger.kernel.org
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
(cherry picked from commit 00983519214b61c1b9371ec2ed55a4dde773e384)
[Jani: s/dev_priv->vbt.edp.low_vswing/dev_priv->edp_low_vswing/ to backport]
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
index 94e6deb4b910291dcd769f391482876051fe3e71..3b57bf06abe8598c1c3b6fba0dc8e19b7f192619 100644 (file)
--- a/drivers/gpu/drm/i915/intel_ddi.c
+++ b/drivers/gpu/drm/i915/intel_ddi.c
@@ -443,9 +443,17 @@ void intel_prepare_ddi_buffer(struct intel_encoder *encoder)
        } else if (IS_BROADWELL(dev_priv)) {
                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;