dm: core: Add a note about how livetree updates work

The unflattening algorithm results in a single block of memory being
allocated for the whole tree. When writing new properties, these are
allocated new memory outside that block. When the block is freed, the
allocated properties remain.

Document how this works and the potential memory leak, as well as
mentioning that updating the livetree is actually supported now.

Signed-off-by: Simon Glass <sjg@chromium.org>

diff --git a/doc/develop/driver-model/livetree.rst b/doc/develop/driver-model/livetree.rst
index 9f654f3b89446348b4fabc567d2f785401e468a6..fb2969259d0780b4f67e3208968d397a240e9bb7 100644 (file)
--- a/doc/develop/driver-model/livetree.rst
+++ b/doc/develop/driver-model/livetree.rst
@@ -211,9 +211,18 @@ using it in new code.
 Modifying the livetree
 ----------------------
 
-This is not currently supported. Once implemented it should provide a much
-more efficient implementation for modification of the device tree than using
-the flat tree.
+This is supported in a limited way, with ofnode_write_prop() and related
+functions.
+
+The unflattening algorithm results in a single block of memory being
+allocated for the whole tree. When writing new properties, these are
+allocated new memory outside that block. When the block is freed, the
+allocated properties remain. This can result in a memory leak.
+
+The solution to this leak would be to add a flag for properties (and nodes when
+support is provided for adding those) that indicates that they should be
+freed. Then the tree can be scanned for these 'separately allocated' nodes and
+properties before freeing the memory block.
 
 
 Internal implementation
@@ -281,6 +290,6 @@ Live tree support was introduced in U-Boot 2017.07. There is still quite a bit
 of work to do to flesh this out:
 
 - tests for all access functions
-- support for livetree modification
+- more support for livetree modification
 - addition of more access functions as needed
 - support for livetree in SPL and before relocation (if desired)

diff --git a/include/dm/ofnode.h b/include/dm/ofnode.h
index 346b09c7d96a53a75c7095fff36fbc04be4c274a..5a5309d79a70f87cfa9b9938895169e1c951ee56 100644 (file)
--- a/include/dm/ofnode.h
+++ b/include/dm/ofnode.h
@@ -1081,7 +1081,8 @@ int ofnode_device_is_compatible(ofnode node, const char *compat);
  * ofnode_write_prop() - Set a property of a ofnode
  *
  * Note that the value passed to the function is *not* allocated by the
- * function itself, but must be allocated by the caller if necessary.
+ * function itself, but must be allocated by the caller if necessary. However
+ * it does allocate memory for the property struct and name.
  *
  * @node:      The node for whose property should be set
  * @propname:  The name of the property to set