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diff --git a/Documentation/devicetree/of_selftest.txt b/Documentation/devicetree/of_selftest.txt deleted file mode 100644 index 57a808b588bf..000000000000 --- a/Documentation/devicetree/of_selftest.txt +++ /dev/null @@ -1,197 +0,0 @@ -Open Firmware Device Tree Selftest ----------------------------------- - -Author: Gaurav Minocha <gaurav.minocha.os@gmail.com> - -1. Introduction - -This document explains how the test data required for executing OF selftest -is attached to the live tree dynamically, independent of the machine's -architecture. - -It is recommended to read the following documents before moving ahead. - -[1] Documentation/devicetree/usage-model.txt -[2] http://www.devicetree.org/Device_Tree_Usage - -OF Selftest has been designed to test the interface (include/linux/of.h) -provided to device driver developers to fetch the device information..etc. -from the unflattened device tree data structure. This interface is used by -most of the device drivers in various use cases. - - -2. Test-data - -The Device Tree Source file (drivers/of/testcase-data/testcases.dts) contains -the test data required for executing the unit tests automated in -drivers/of/selftests.c. Currently, following Device Tree Source Include files -(.dtsi) are included in testcase.dts: - -drivers/of/testcase-data/tests-interrupts.dtsi -drivers/of/testcase-data/tests-platform.dtsi -drivers/of/testcase-data/tests-phandle.dtsi -drivers/of/testcase-data/tests-match.dtsi - -When the kernel is build with OF_SELFTEST enabled, then the following make rule - -$(obj)/%.dtb: $(src)/%.dts FORCE - $(call if_changed_dep, dtc) - -is used to compile the DT source file (testcase.dts) into a binary blob -(testcase.dtb), also referred as flattened DT. - -After that, using the following rule the binary blob above is wrapped as an -assembly file (testcase.dtb.S). - -$(obj)/%.dtb.S: $(obj)/%.dtb - $(call cmd, dt_S_dtb) - -The assembly file is compiled into an object file (testcase.dtb.o), and is -linked into the kernel image. - - -2.1. Adding the test data - -Un-flattened device tree structure: - -Un-flattened device tree consists of connected device_node(s) in form of a tree -structure described below. - -// following struct members are used to construct the tree -struct device_node { - ... - struct device_node *parent; - struct device_node *child; - struct device_node *sibling; - ... - }; - -Figure 1, describes a generic structure of machine's un-flattened device tree -considering only child and sibling pointers. There exists another pointer, -*parent, that is used to traverse the tree in the reverse direction. So, at -a particular level the child node and all the sibling nodes will have a parent -pointer pointing to a common node (e.g. child1, sibling2, sibling3, sibling4's -parent points to root node) - -root ('/') - | -child1 -> sibling2 -> sibling3 -> sibling4 -> null - | | | | - | | | null - | | | - | | child31 -> sibling32 -> null - | | | | - | | null null - | | - | child21 -> sibling22 -> sibling23 -> null - | | | | - | null null null - | -child11 -> sibling12 -> sibling13 -> sibling14 -> null - | | | | - | | | null - | | | - null null child131 -> null - | - null - -Figure 1: Generic structure of un-flattened device tree - - -Before executing OF selftest, it is required to attach the test data to -machine's device tree (if present). So, when selftest_data_add() is called, -at first it reads the flattened device tree data linked into the kernel image -via the following kernel symbols: - -__dtb_testcases_begin - address marking the start of test data blob -__dtb_testcases_end - address marking the end of test data blob - -Secondly, it calls of_fdt_unflatten_tree() to unflatten the flattened -blob. And finally, if the machine's device tree (i.e live tree) is present, -then it attaches the unflattened test data tree to the live tree, else it -attaches itself as a live device tree. - -attach_node_and_children() uses of_attach_node() to attach the nodes into the -live tree as explained below. To explain the same, the test data tree described - in Figure 2 is attached to the live tree described in Figure 1. - -root ('/') - | - testcase-data - | - test-child0 -> test-sibling1 -> test-sibling2 -> test-sibling3 -> null - | | | | - test-child01 null null null - - -Figure 2: Example test data tree to be attached to live tree. - -According to the scenario above, the live tree is already present so it isn't -required to attach the root('/') node. All other nodes are attached by calling -of_attach_node() on each node. - -In the function of_attach_node(), the new node is attached as the child of the -given parent in live tree. But, if parent already has a child then the new node -replaces the current child and turns it into its sibling. So, when the testcase -data node is attached to the live tree above (Figure 1), the final structure is - as shown in Figure 3. - -root ('/') - | -testcase-data -> child1 -> sibling2 -> sibling3 -> sibling4 -> null - | | | | | - (...) | | | null - | | child31 -> sibling32 -> null - | | | | - | | null null - | | - | child21 -> sibling22 -> sibling23 -> null - | | | | - | null null null - | - child11 -> sibling12 -> sibling13 -> sibling14 -> null - | | | | - null null | null - | - child131 -> null - | - null ------------------------------------------------------------------------ - -root ('/') - | -testcase-data -> child1 -> sibling2 -> sibling3 -> sibling4 -> null - | | | | | - | (...) (...) (...) null - | -test-sibling3 -> test-sibling2 -> test-sibling1 -> test-child0 -> null - | | | | - null null null test-child01 - - -Figure 3: Live device tree structure after attaching the testcase-data. - - -Astute readers would have noticed that test-child0 node becomes the last -sibling compared to the earlier structure (Figure 2). After attaching first -test-child0 the test-sibling1 is attached that pushes the child node -(i.e. test-child0) to become a sibling and makes itself a child node, - as mentioned above. - -If a duplicate node is found (i.e. if a node with same full_name property is -already present in the live tree), then the node isn't attached rather its -properties are updated to the live tree's node by calling the function -update_node_properties(). - - -2.2. Removing the test data - -Once the test case execution is complete, selftest_data_remove is called in -order to remove the device nodes attached initially (first the leaf nodes are -detached and then moving up the parent nodes are removed, and eventually the -whole tree). selftest_data_remove() calls detach_node_and_children() that uses -of_detach_node() to detach the nodes from the live device tree. - -To detach a node, of_detach_node() either updates the child pointer of given -node's parent to its sibling or attaches the previous sibling to the given -node's sibling, as appropriate. That is it :) |