drm/i915/bios: add legacy contents to common child device config

Add legacy contents to common child device config, in preparation for
using a single child device config. Use unions where BDB versions of the
config differ. Use the naming from old_child_dev_config for legacy
fields.

No functional changes.

Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/b606456da4d52f1aedf383aab4275d81013d3178.1503600621.git.jani.nikula@intel.com

drivers/gpu/drm/i915/intel_vbt_defs.h

@@ -257,27 +257,49 @@ struct old_child_dev_config {
 	u8  dvo_function;
 } __packed;
 
-/* This one contains field offsets that are known to be common for all BDB
- * versions. Notice that the meaning of the contents contents may still change,
- * but at least the offsets are consistent. */
+/*
+ * The child device config, aka the display device data structure, provides a
+ * description of a port and its configuration on the platform.
+ *
+ * The child device config size has been increased, and fields have been added
+ * and their meaning has changed over time. Care must be taken when accessing
+ * basically any of the fields to ensure the correct interpretation for the BDB
+ * version in question.
+ *
+ * When we copy the child device configs to dev_priv->vbt.child_dev, we reserve
+ * space for the full structure below, and initialize the tail not actually
+ * present in VBT to zeros. Accessing those fields is fine, as long as the
+ * default zero is taken into account, again according to the BDB version.
+ *
+ * BDB versions 155 and below are considered legacy, and version 155 seems to be
+ * a baseline for some of the VBT documentation. When adding new fields, please
+ * include the BDB version when the field was added, if it's above that.
+ */
 struct common_child_dev_config {
 	u16 handle;
 	u16 device_type;
-	u8 i2c_speed;
-	u8 dp_onboard_redriver;					/* 158 */
-	u8 dp_ondock_redriver;					/* 158 */
-	u8 hdmi_level_shifter_value:4;				/* 169 */
-	u8 hdmi_max_data_rate:4;				/* 204 */
-	u16 dtd_buf_ptr;					/* 161 */
-	u8 edidless_efp:1;					/* 161 */
-	u8 compression_enable:1;				/* 198 */
-	u8 compression_method:1;				/* 198 */
-	u8 ganged_edp:1;					/* 202 */
-	u8 reserved0:4;
-	u8 compression_structure_index:4;			/* 198 */
-	u8 reserved1:4;
-	u8 slave_port;						/* 202 */
-	u8 reserved2;
+
+	union {
+		u8  device_id[10]; /* ascii string */
+		struct {
+			u8 i2c_speed;
+			u8 dp_onboard_redriver;			/* 158 */
+			u8 dp_ondock_redriver;			/* 158 */
+			u8 hdmi_level_shifter_value:4;		/* 169 */
+			u8 hdmi_max_data_rate:4;		/* 204 */
+			u16 dtd_buf_ptr;			/* 161 */
+			u8 edidless_efp:1;			/* 161 */
+			u8 compression_enable:1;		/* 198 */
+			u8 compression_method:1;		/* 198 */
+			u8 ganged_edp:1;			/* 202 */
+			u8 reserved0:4;
+			u8 compression_structure_index:4;	/* 198 */
+			u8 reserved1:4;
+			u8 slave_port;				/* 202 */
+			u8 reserved2;
+		} __packed;
+	} __packed;
+
 	u16 addin_offset;
 	u8 dvo_port;
 	u8 i2c_pin;
@@ -285,21 +307,38 @@ struct common_child_dev_config {
 	u8 ddc_pin;
 	u16 edid_ptr;
 	u8 dvo_cfg; /* See DEVICE_CFG_* above */
-	u8 efp_routed:1;					/* 158 */
-	u8 lane_reversal:1;					/* 184 */
-	u8 lspcon:1;						/* 192 */
-	u8 iboost:1;						/* 196 */
-	u8 hpd_invert:1;					/* 196 */
-	u8 flag_reserved:3;
-	u8 hdmi_support:1;					/* 158 */
-	u8 dp_support:1;					/* 158 */
-	u8 tmds_support:1;					/* 158 */
-	u8 support_reserved:5;
-	u8 aux_channel;
-	u8 dongle_detect;
+
+	union {
+		struct {
+			u8 dvo2_port;
+			u8 i2c2_pin;
+			u8 slave2_addr;
+			u8 ddc2_pin;
+		} __packed;
+		struct {
+			u8 efp_routed:1;			/* 158 */
+			u8 lane_reversal:1;			/* 184 */
+			u8 lspcon:1;				/* 192 */
+			u8 iboost:1;				/* 196 */
+			u8 hpd_invert:1;			/* 196 */
+			u8 flag_reserved:3;
+			u8 hdmi_support:1;			/* 158 */
+			u8 dp_support:1;			/* 158 */
+			u8 tmds_support:1;			/* 158 */
+			u8 support_reserved:5;
+			u8 aux_channel;
+			u8 dongle_detect;
+		} __packed;
+	} __packed;
+
 	u8 capabilities;
 	u8 dvo_wiring; /* See DEVICE_WIRE_* above */
-	u8 mipi_bridge_type;					/* 171 */
+
+	union {
+		u8 dvo2_wiring;
+		u8 mipi_bridge_type;				/* 171 */
+	} __packed;
+
 	u16 extended_type;
 	u8 dvo_function;
 	u8 flags2;						/* 195 */