Revert "drm/i915: Allow parsing of variable size child device entries from VBT"

This reverts

commit 047fe6e6
Author: David Weinehall <david.weinehall@linux.intel.com>
Date:   Tue Aug 4 16:55:52 2015 +0300

    drm/i915: Allow parsing of variable size child device entries from VBT

That commit is not valid for v4.2, however it will be valid for v4.3. It
was simply queued too early.

The referenced regressing commit is just fine until the size of struct
common_child_dev_config changes, and that won't happen until
v4.3. Indeed, the expected size checks here rely on the increased size
of the struct, breaking new platforms.

Fixes: 047fe6e6 ("drm/i915: Allow parsing of variable size child device entries from VBT")
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Weinehall <david.weinehall@linux.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>

drivers/gpu/drm/i915/intel_bios.c

@@ -1075,7 +1075,6 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
 	const union child_device_config *p_child;
 	union child_device_config *child_dev_ptr;
 	int i, child_device_num, count;
-	u8 expected_size;
 	u16	block_size;
 
 	p_defs = find_section(bdb, BDB_GENERAL_DEFINITIONS);
@@ -1083,26 +1082,8 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
 		DRM_DEBUG_KMS("No general definition block is found, no devices defined.\n");
 		return;
 	}
-	if (bdb->version < 195) {
-		expected_size = 33;
-	} else if (bdb->version == 195) {
-		expected_size = 37;
-	} else if (bdb->version <= 197) {
-		expected_size = 38;
-	} else {
-		expected_size = 38;
-		DRM_DEBUG_DRIVER("Expected child_device_config size for BDB version %u not known; assuming %u\n",
-				 expected_size, bdb->version);
-	}
-
-	if (expected_size > sizeof(*p_child)) {
-		DRM_ERROR("child_device_config cannot fit in p_child\n");
-		return;
-	}
-
-	if (p_defs->child_dev_size != expected_size) {
-		DRM_ERROR("Size mismatch; child_device_config size=%u (expected %u); bdb->version: %u\n",
-			  p_defs->child_dev_size, expected_size, bdb->version);
+	if (p_defs->child_dev_size < sizeof(*p_child)) {
+		DRM_ERROR("General definiton block child device size is too small.\n");
 		return;
 	}
 	/* get the block size of general definitions */
@@ -1149,7 +1130,7 @@ parse_device_mapping(struct drm_i915_private *dev_priv,
 
 		child_dev_ptr = dev_priv->vbt.child_dev + count;
 		count++;
-		memcpy(child_dev_ptr, p_child, p_defs->child_dev_size);
+		memcpy(child_dev_ptr, p_child, sizeof(*p_child));
 	}
 	return;
 }