Based on kernel version 6.11
. Page generated on 2024-09-24 08:21 EST
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 | .. SPDX-License-Identifier: GPL-2.0 ================================= Open Firmware Devicetree Unittest ================================= Author: Gaurav Minocha <gaurav.minocha.os@gmail.com> 1. Introduction =============== This document explains how the test data required for executing OF unittest 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.rst (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. Verbose Output (EXPECT) ========================== If unittest detects a problem it will print a warning or error message to the console. Unittest also triggers warning and error messages from other kernel code as a result of intentionally bad unittest data. This has led to confusion as to whether the triggered messages are an expected result of a test or whether there is a real problem that is independent of unittest. 'EXPECT \ : text' (begin) and 'EXPECT / : text' (end) messages have been added to unittest to report that a warning or error is expected. The begin is printed before triggering the warning or error, and the end is printed after triggering the warning or error. The EXPECT messages result in very noisy console messages that are difficult to read. The script scripts/dtc/of_unittest_expect was created to filter this verbosity and highlight mismatches between triggered warnings and errors vs expected warnings and errors. More information is available from 'scripts/dtc/of_unittest_expect --help'. 3. Test-data ============ The Device Tree Source file (drivers/of/unittest-data/testcases.dts) contains the test data required for executing the unit tests automated in drivers/of/unittest.c. Currently, following Device Tree Source Include files (.dtsi) are included in testcases.dts:: drivers/of/unittest-data/tests-interrupts.dtsi drivers/of/unittest-data/tests-platform.dtsi drivers/of/unittest-data/tests-phandle.dtsi drivers/of/unittest-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 (testcases.dts) into a binary blob (testcases.dtb), also referred as flattened DT. After that, using the following rule the binary blob above is wrapped as an assembly file (testcases.dtb.S):: $(obj)/%.dtb.S: $(obj)/%.dtb $(call cmd, dt_S_dtb) The assembly file is compiled into an object file (testcases.dtb.o), and is linked into the kernel image. 3.1. 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 unittest, 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(). 3.2. 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 :) |