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dm: core: Prepare for updating the device tree with ofnode

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Add some documentation and a new flag so that we can safely enabled using
the ofnode interface to write to the device tree.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass 2022-07-30 15:52:12 -06:00 committed by Tom Rini
parent b7eaa4f5e5
commit 7b1dfc9fd7
3 changed files with 30 additions and 1 deletions
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26
doc/develop/driver-model/livetree.rst
View file

@ -224,6 +224,32 @@ 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 use a flag UT_TESTF_LIVE_OR_FLAT then ensures
that tests which write to the flat tree are not run if OF_LIVE is enabled. Only
the live tree version of the test is run, when OF_LIVE is enabled, with
sandbox_flattree running the flat tree version.
This is of course a work-around, even if a reasonable one. One solution to this
problem would be to make a copy of the flat tree before the test and restore it
afterwards, in the same memory location, so that the live tree pointers work
again. Another would be to regenerate the live tree if a test modified the flat
tree.
Neither of these solutions is currently implemented, since the situation that
causes the problem can only occur in sandbox tests, is somewhat esoteric and
the UT_TESTF_LIVE_OR_FLAT flag deals with it in a reasonable way.
Multiple livetrees
------------------

2
include/test/test.h
View file

@ -46,6 +46,8 @@ enum {
UT_TESTF_CONSOLE_REC = BIT(5), /* needs console recording */
/* do extra driver model init and uninit */
UT_TESTF_DM = BIT(6),
/* live or flat device tree, but not both in the same executable */
UT_TESTF_LIVE_OR_FLAT = BIT(4),
};
/**

3
test/test-main.c
View file

@ -338,7 +338,8 @@ static int ut_run_test_live_flat(struct unit_test_state *uts,
/* Run with the live tree if possible */
runs = 0;
if (CONFIG_IS_ENABLED(OF_LIVE)) {
if (!(test->flags & UT_TESTF_FLAT_TREE)) {
if (!(test->flags &
(UT_TESTF_FLAT_TREE | UT_TESTF_LIVE_OR_FLAT))) {
uts->of_live = true;
ut_assertok(ut_run_test(uts, test, test->name));
runs++;