1.. SPDX-License-Identifier: GPL-2.0 2 3================================= 4Open Firmware Devicetree Unittest 5================================= 6 7Author: Gaurav Minocha <gaurav.minocha.os@gmail.com> 8 91. Introduction 10=============== 11 12This document explains how the test data required for executing OF unittest 13is attached to the live tree dynamically, independent of the machine's 14architecture. 15 16It is recommended to read the following documents before moving ahead. 17 18(1) Documentation/devicetree/usage-model.rst 19(2) http://www.devicetree.org/Device_Tree_Usage 20 21OF Selftest has been designed to test the interface (include/linux/of.h) 22provided to device driver developers to fetch the device information..etc. 23from the unflattened device tree data structure. This interface is used by 24most of the device drivers in various use cases. 25 26 272. Verbose Output (EXPECT) 28========================== 29 30If unittest detects a problem it will print a warning or error message to 31the console. Unittest also triggers warning and error messages from other 32kernel code as a result of intentionally bad unittest data. This has led 33to confusion as to whether the triggered messages are an expected result 34of a test or whether there is a real problem that is independent of unittest. 35 36'EXPECT \ : text' (begin) and 'EXPECT / : text' (end) messages have been 37added to unittest to report that a warning or error is expected. The 38begin is printed before triggering the warning or error, and the end is 39printed after triggering the warning or error. 40 41The EXPECT messages result in very noisy console messages that are difficult 42to read. The script scripts/dtc/of_unittest_expect was created to filter 43this verbosity and highlight mismatches between triggered warnings and 44errors vs expected warnings and errors. More information is available 45from 'scripts/dtc/of_unittest_expect --help'. 46 47 483. Test-data 49============ 50 51The Device Tree Source file (drivers/of/unittest-data/testcases.dts) contains 52the test data required for executing the unit tests automated in 53drivers/of/unittest.c. Currently, following Device Tree Source Include files 54(.dtsi) are included in testcases.dts:: 55 56 drivers/of/unittest-data/tests-interrupts.dtsi 57 drivers/of/unittest-data/tests-platform.dtsi 58 drivers/of/unittest-data/tests-phandle.dtsi 59 drivers/of/unittest-data/tests-match.dtsi 60 61When the kernel is build with OF_SELFTEST enabled, then the following make 62rule:: 63 64 $(obj)/%.dtb: $(src)/%.dts FORCE 65 $(call if_changed_dep, dtc) 66 67is used to compile the DT source file (testcases.dts) into a binary blob 68(testcases.dtb), also referred as flattened DT. 69 70After that, using the following rule the binary blob above is wrapped as an 71assembly file (testcases.dtb.S):: 72 73 $(obj)/%.dtb.S: $(obj)/%.dtb 74 $(call cmd, dt_S_dtb) 75 76The assembly file is compiled into an object file (testcases.dtb.o), and is 77linked into the kernel image. 78 79 803.1. Adding the test data 81------------------------- 82 83Un-flattened device tree structure: 84 85Un-flattened device tree consists of connected device_node(s) in form of a tree 86structure described below:: 87 88 // following struct members are used to construct the tree 89 struct device_node { 90 ... 91 struct device_node *parent; 92 struct device_node *child; 93 struct device_node *sibling; 94 ... 95 }; 96 97Figure 1, describes a generic structure of machine's un-flattened device tree 98considering only child and sibling pointers. There exists another pointer, 99``*parent``, that is used to traverse the tree in the reverse direction. So, at 100a particular level the child node and all the sibling nodes will have a parent 101pointer pointing to a common node (e.g. child1, sibling2, sibling3, sibling4's 102parent points to root node):: 103 104 root ('/') 105 | 106 child1 -> sibling2 -> sibling3 -> sibling4 -> null 107 | | | | 108 | | | null 109 | | | 110 | | child31 -> sibling32 -> null 111 | | | | 112 | | null null 113 | | 114 | child21 -> sibling22 -> sibling23 -> null 115 | | | | 116 | null null null 117 | 118 child11 -> sibling12 -> sibling13 -> sibling14 -> null 119 | | | | 120 | | | null 121 | | | 122 null null child131 -> null 123 | 124 null 125 126Figure 1: Generic structure of un-flattened device tree 127 128 129Before executing OF unittest, it is required to attach the test data to 130machine's device tree (if present). So, when selftest_data_add() is called, 131at first it reads the flattened device tree data linked into the kernel image 132via the following kernel symbols:: 133 134 __dtb_testcases_begin - address marking the start of test data blob 135 __dtb_testcases_end - address marking the end of test data blob 136 137Secondly, it calls of_fdt_unflatten_tree() to unflatten the flattened 138blob. And finally, if the machine's device tree (i.e live tree) is present, 139then it attaches the unflattened test data tree to the live tree, else it 140attaches itself as a live device tree. 141 142attach_node_and_children() uses of_attach_node() to attach the nodes into the 143live tree as explained below. To explain the same, the test data tree described 144in Figure 2 is attached to the live tree described in Figure 1:: 145 146 root ('/') 147 | 148 testcase-data 149 | 150 test-child0 -> test-sibling1 -> test-sibling2 -> test-sibling3 -> null 151 | | | | 152 test-child01 null null null 153 154 155Figure 2: Example test data tree to be attached to live tree. 156 157According to the scenario above, the live tree is already present so it isn't 158required to attach the root('/') node. All other nodes are attached by calling 159of_attach_node() on each node. 160 161In the function of_attach_node(), the new node is attached as the child of the 162given parent in live tree. But, if parent already has a child then the new node 163replaces the current child and turns it into its sibling. So, when the testcase 164data node is attached to the live tree above (Figure 1), the final structure is 165as shown in Figure 3:: 166 167 root ('/') 168 | 169 testcase-data -> child1 -> sibling2 -> sibling3 -> sibling4 -> null 170 | | | | | 171 (...) | | | null 172 | | child31 -> sibling32 -> null 173 | | | | 174 | | null null 175 | | 176 | child21 -> sibling22 -> sibling23 -> null 177 | | | | 178 | null null null 179 | 180 child11 -> sibling12 -> sibling13 -> sibling14 -> null 181 | | | | 182 null null | null 183 | 184 child131 -> null 185 | 186 null 187 ----------------------------------------------------------------------- 188 189 root ('/') 190 | 191 testcase-data -> child1 -> sibling2 -> sibling3 -> sibling4 -> null 192 | | | | | 193 | (...) (...) (...) null 194 | 195 test-sibling3 -> test-sibling2 -> test-sibling1 -> test-child0 -> null 196 | | | | 197 null null null test-child01 198 199 200Figure 3: Live device tree structure after attaching the testcase-data. 201 202 203Astute readers would have noticed that test-child0 node becomes the last 204sibling compared to the earlier structure (Figure 2). After attaching first 205test-child0 the test-sibling1 is attached that pushes the child node 206(i.e. test-child0) to become a sibling and makes itself a child node, 207as mentioned above. 208 209If a duplicate node is found (i.e. if a node with same full_name property is 210already present in the live tree), then the node isn't attached rather its 211properties are updated to the live tree's node by calling the function 212update_node_properties(). 213 214 2153.2. Removing the test data 216--------------------------- 217 218Once the test case execution is complete, selftest_data_remove is called in 219order to remove the device nodes attached initially (first the leaf nodes are 220detached and then moving up the parent nodes are removed, and eventually the 221whole tree). selftest_data_remove() calls detach_node_and_children() that uses 222of_detach_node() to detach the nodes from the live device tree. 223 224To detach a node, of_detach_node() either updates the child pointer of given 225node's parent to its sibling or attaches the previous sibling to the given 226node's sibling, as appropriate. That is it :) 227