drm/i915/skl: Only use the 800mV+2bB HDMI translation entry

This translation entry was updated after electrical validation by the hw
team. The other entries are removed from existence as they aren't
validated and because the sole use of a certain type of level shifter
for SKL products is anticipated.

v2: Remove all the other entries and force the use of the 800mv+2dB
    config (Sonika)
Suggested-by: NSonika Jindal <sonika.jindal@intel.com>
Cc: Sonika Jindal <sonika.jindal@intel.com>
Signed-off-by: NDamien Lespiau <damien.lespiau@intel.com>
Reviewed-by: NSonika Jindal <sonika.jindal@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_ddi.c

@@ -156,16 +156,7 @@ static const struct ddi_buf_trans skl_ddi_translations_edp[] = {
 
 static const struct ddi_buf_trans skl_ddi_translations_hdmi[] = {
 					/* Idx	NT mV   T mV    db  */
-	{ 0x00000018, 0x000000a0 },	/* 0:	400	400	0   */
-	{ 0x00004014, 0x00000098 },	/* 1:	400	600	3.5 */
-	{ 0x00006012, 0x00000088 },	/* 2:	400	800	6   */
-	{ 0x00000018, 0x0000003c },	/* 3:	450	450	0   */
-	{ 0x00000018, 0x00000098 },	/* 4:	600	600	0   */
-	{ 0x00003015, 0x00000088 },	/* 5:	600	800	2.5 */
-	{ 0x00005013, 0x00000080 },	/* 6:	600	1000	4.5 */
-	{ 0x00000018, 0x00000088 },	/* 7:	800	800	0   */
-	{ 0x00000096, 0x00000080 },	/* 8:	800	1000	2   */
-	{ 0x00000018, 0x00000080 },	/* 9:	1200	1200	0   */
+	{ 0x00004014, 0x00000087 },	/* 0:	800	1000	2   */
 };
 
 enum port intel_ddi_get_encoder_port(struct intel_encoder *intel_encoder)
@@ -202,7 +193,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
 {
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	u32 reg;
-	int i, n_hdmi_entries, n_dp_entries, n_edp_entries, hdmi_800mV_0dB,
+	int i, n_hdmi_entries, n_dp_entries, n_edp_entries, hdmi_default_entry,
 	    size;
 	int hdmi_level = dev_priv->vbt.ddi_port_info[port].hdmi_level_shift;
 	const struct ddi_buf_trans *ddi_translations_fdi;
@@ -223,9 +214,16 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
 			n_edp_entries = ARRAY_SIZE(skl_ddi_translations_dp);
 		}
 
+		/*
+		 * On SKL, the recommendation from the hw team is to always use
+		 * a certain type of level shifter (and thus the corresponding
+		 * 800mV+2dB entry). Given that's the only validated entry, we
+		 * override what is in the VBT, at least until further notice.
+		 */
+		hdmi_level = 0;
 		ddi_translations_hdmi = skl_ddi_translations_hdmi;
 		n_hdmi_entries = ARRAY_SIZE(skl_ddi_translations_hdmi);
-		hdmi_800mV_0dB = 7;
+		hdmi_default_entry = 0;
 	} else if (IS_BROADWELL(dev)) {
 		ddi_translations_fdi = bdw_ddi_translations_fdi;
 		ddi_translations_dp = bdw_ddi_translations_dp;
@@ -234,7 +232,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
 		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_800mV_0dB = 7;
+		hdmi_default_entry = 7;
 	} else if (IS_HASWELL(dev)) {
 		ddi_translations_fdi = hsw_ddi_translations_fdi;
 		ddi_translations_dp = hsw_ddi_translations_dp;
@@ -242,7 +240,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
 		ddi_translations_hdmi = hsw_ddi_translations_hdmi;
 		n_dp_entries = n_edp_entries = ARRAY_SIZE(hsw_ddi_translations_dp);
 		n_hdmi_entries = ARRAY_SIZE(hsw_ddi_translations_hdmi);
-		hdmi_800mV_0dB = 6;
+		hdmi_default_entry = 6;
 	} else {
 		WARN(1, "ddi translation table missing\n");
 		ddi_translations_edp = bdw_ddi_translations_dp;
@@ -252,7 +250,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
 		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_800mV_0dB = 7;
+		hdmi_default_entry = 7;
 	}
 
 	switch (port) {
@@ -295,7 +293,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
 	/* Choose a good default if VBT is badly populated */
 	if (hdmi_level == HDMI_LEVEL_SHIFT_UNKNOWN ||
 	    hdmi_level >= n_hdmi_entries)
-		hdmi_level = hdmi_800mV_0dB;
+		hdmi_level = hdmi_default_entry;
 
 	/* Entry 9 is for HDMI: */
 	I915_WRITE(reg, ddi_translations_hdmi[hdmi_level].trans1);