[PATCH] ACPI / property: fix handling of data_nodes in acpi_get_next_subnode()

[Pierre-Louis Bossart]

When the DSDT tables expose devices with subdevices and a set of
hierarchical _DSD properties, the data returned by
acpi_get_next_subnode() is incorrect, with the results suggesting a bad
pointer assignment. The parser works fine with device_nodes or
data_nodes, but not with a combination of the two.

The problem is traced to an invalid pointer used when jumping from
handling device_nodes to data nodes. The existing code looks for data
nodes below the last subdevice found instead of the common root. Fix
by forcing the acpi_device pointer to be derived from the same fwnode
for the two types of subnodes.

This same problem of handling device and data nodes was already fixed
in a similar way by 'commit bf4703fdd166 ("ACPI / property: fix data
node parsing in acpi_get_next_subnode()")' but broken later by 'commit
34055190b19 ("ACPI / property: Add fwnode_get_next_child_node()")', so
this should probably go to linux-stable all the way to 4.12

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
---
 drivers/acpi/property.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
index 5815356ea6ad..efc74f912f39 100644
--- a/drivers/acpi/property.c
+++ b/drivers/acpi/property.c
@@ -943,6 +943,16 @@ struct fwnode_handle *acpi_get_next_subnode(const struct fwnode_handle *fwnode,
 		const struct acpi_data_node *data = to_acpi_data_node(fwnode);
 		struct acpi_data_node *dn;
 
+		/*
+		 * We can have a combination of device and data nodes,
+		 * e.g. with hierarchical _DSD properties. Make sure
+		 * the adev pointer is restored before going through
+		 * data nodes, otherwise we will be looking for
+		 * data_nodes below the last device found instead of
+		 * the common fwnode shared by device_nodes and
+		 * data_nodes
+		 */
+		adev = to_acpi_device_node(fwnode);
 		if (adev)
 			head = &adev->data.subnodes;
 		else if (data)
-- 
2.17.1