drm/edid: do invalid block filtering in-place

Rewrite edid_filter_invalid_blocks() to filter invalid blocks
in-place. The main motivation is to not rely on passed in information on
invalid block count or the allocation size, which will be helpful in
follow-up work on HF-EEODB.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/a6ad5e4e7b91338c0d19d7be189af31094e65555.1656494768.git.jani.nikula@intel.com

drivers/gpu/drm/drm_edid.c

@@ -2020,32 +2020,36 @@ bool drm_edid_is_valid(struct edid *edid)
 }
 EXPORT_SYMBOL(drm_edid_is_valid);
 
-static struct edid *edid_filter_invalid_blocks(const struct edid *edid,
-					       int invalid_blocks,
+static struct edid *edid_filter_invalid_blocks(struct edid *edid,
 					       size_t *alloc_size)
 {
-	struct edid *new, *dest_block;
-	int valid_extensions = edid->extensions - invalid_blocks;
-	int i;
+	struct edid *new;
+	int i, valid_blocks = 0;
 
-	*alloc_size = edid_size_by_blocks(valid_extensions + 1);
+	for (i = 0; i < edid_block_count(edid); i++) {
+		const void *src_block = edid_block_data(edid, i);
 
-	new = kmalloc(*alloc_size, GFP_KERNEL);
-	if (!new)
-		goto out;
+		if (edid_block_valid(src_block, i == 0)) {
+			void *dst_block = (void *)edid_block_data(edid, valid_blocks);
 
-	dest_block = new;
-	for (i = 0; i < edid_block_count(edid); i++) {
-		const void *block = edid_block_data(edid, i);
+			memmove(dst_block, src_block, EDID_LENGTH);
+			valid_blocks++;
+		}
+	}
 
-		if (edid_block_valid(block, i == 0))
-			memcpy(dest_block++, block, EDID_LENGTH);
+	/* We already trusted the base block to be valid here... */
+	if (WARN_ON(!valid_blocks)) {
+		kfree(edid);
+		return NULL;
 	}
 
-	new->extensions = valid_extensions;
-	new->checksum = edid_block_compute_checksum(new);
+	edid->extensions = valid_blocks - 1;
+	edid->checksum = edid_block_compute_checksum(edid);
 
-out:
+	*alloc_size = edid_size_by_blocks(valid_blocks);
+
+	new = krealloc(edid, *alloc_size, GFP_KERNEL);
+	if (!new)
 		kfree(edid);
 
 	return new;
@@ -2316,8 +2320,7 @@ static struct edid *_drm_do_get_edid(struct drm_connector *connector,
 	if (invalid_blocks) {
 		connector_bad_edid(connector, edid, edid_block_count(edid));
 
-		edid = edid_filter_invalid_blocks(edid, invalid_blocks,
-						  &alloc_size);
+		edid = edid_filter_invalid_blocks(edid, &alloc_size);
 	}
 
 ok: