dm: core: Allow copying ofnode property data when writing

[platform/kernel/u-boot.git] / doc / develop / driver-model / livetree.rst

diff --git a/doc/develop/driver-model/livetree.rst b/doc/develop/driver-model/livetree.rst
index c29f29b..55aa3ea 100644 (file)
--- a/doc/develop/driver-model/livetree.rst
+++ b/doc/develop/driver-model/livetree.rst
@@ -224,6 +224,21 @@ 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.
 
+The ofnode_write\_...() functions also support writing to the flat tree. Care
+should be taken however, since this can change the position of node names and
+properties in the flat tree, thus affecting the live tree. Generally this does
+not matter, since when we fire up the live tree we don't ever use the flat tree
+again. But in the case of tests, this can cause a problem.
+
+The sandbox tests typically run with OF_LIVE enabled but with the actual live
+tree either present or absent. This is to make sure that the flat tree functions
+work correctly even with OF_LIVE is enabled. But if a test modifies the flat
+device tree, then the live tree can become invalid. Any live tree tests that run
+after that point will use a corrupted tree, e.g. with an incorrect property name
+or worse. To deal with this we take a copy of the device tree and restore it
+after any test that modifies it. Note that this copy is not made on other
+boards, only sandbox.
+
 
 Multiple livetrees
 ------------------
@@ -235,11 +250,14 @@ a flat tree.
 It would be helpful to use livetree for fixups, since adding a lot of nodes and
 properties would involve less memory copying and be more efficient. As a step
 towards this, an `oftree` type has been introduced. It is normally set to
-oftree_default() but can be set to other values. Eventually this should allow
-the use of FDT fixups using the ofnode interface, instead of the low-level
-libfdt one.
+oftree_default() but can be set to other values using oftree_from_fdt().
+So long as OF_LIVE is disabled, it is possible to do fixups using the ofnode
+interface. The OF_LIVE support required addition of the flattening step at the
+end.
 
-See dm_test_ofnode_root() for some examples.
+See dm_test_ofnode_root() for some examples. The ofnode_path_root() function
+causes a flat device tree to be 'registered' such that it can be used by the
+ofnode interface.
 
 
 Internal implementation
@@ -303,10 +321,9 @@ Adding a new function for device-tree access involves the following steps:
 Future work
 -----------
 
-Live tree support was introduced in U-Boot 2017.07. There is still quite a bit
-of work to do to flesh this out:
+Live tree support was introduced in U-Boot 2017.07. Some possible enhancements
+are:
 
-- tests for all access functions
-- more support for livetree modification
-- addition of more access functions as needed
 - support for livetree in SPL and before relocation (if desired)
+- freeing leaked memory caused by writing new nodes / property values to the
+  livetree (ofnode_write_prop())