drm/gma500/cdv: Check vbt config bits when detecting lvds panels

Some machines have an lvds child device in vbt even though a panel is
not attached. To make detection more reliable we now also check the lvds
config bits available in the vbt.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1665766
Cc: stable@vger.kernel.org
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190416114607.1072-1-patrik.r.jakobsson@gmail.com

drivers/gpu/drm/gma500/cdv_intel_lvds.c

@@ -594,6 +594,9 @@ void cdv_intel_lvds_init(struct drm_device *dev,
 	int pipe;
 	u8 pin;
 
+	if (!dev_priv->lvds_enabled_in_vbt)
+		return;
+
 	pin = GMBUS_PORT_PANEL;
 	if (!lvds_is_present_in_vbt(dev, &pin)) {
 		DRM_DEBUG_KMS("LVDS is not present in VBT\n");

drivers/gpu/drm/gma500/intel_bios.c

@@ -436,6 +436,9 @@ parse_driver_features(struct drm_psb_private *dev_priv,
 	if (driver->lvds_config == BDB_DRIVER_FEATURE_EDP)
 		dev_priv->edp.support = 1;
 
+	dev_priv->lvds_enabled_in_vbt = driver->lvds_config != 0;
+	DRM_DEBUG_KMS("LVDS VBT config bits: 0x%x\n", driver->lvds_config);
+
 	/* This bit means to use 96Mhz for DPLL_A or not */
 	if (driver->primary_lfp_id)
 		dev_priv->dplla_96mhz = true;

drivers/gpu/drm/gma500/psb_drv.h

@@ -537,6 +537,7 @@ struct drm_psb_private {
 	int lvds_ssc_freq;
 	bool is_lvds_on;
 	bool is_mipi_on;
+	bool lvds_enabled_in_vbt;
 	u32 mipi_ctrl_display;
 
 	unsigned int core_freq;