On Wed, 3 Sep 2014 00:16:29 -0700, Gaurav Minocha <gaurav.minocha.os@xxxxxxxxx> wrote: > This patch add a document that explains how the selftest test data > is dynamically attached into the live device tree irrespective > of the machine's architecture. > > Signed-off-by: Gaurav Minocha <gaurav.minocha.os@xxxxxxxxx> Applied, thanks. Watch out for trailing whitespace. I had to tidy up many lines. g. > --- > Documentation/devicetree/of_selftest.txt | 204 ++++++++++++++++++++++++++++++ > 1 file changed, 204 insertions(+) > create mode 100644 Documentation/devicetree/of_selftest.txt > > diff --git a/Documentation/devicetree/of_selftest.txt b/Documentation/devicetree/of_selftest.txt > new file mode 100644 > index 0000000..b1d9250 > --- /dev/null > +++ b/Documentation/devicetree/of_selftest.txt > @@ -0,0 +1,204 @@ > +Open Firmware Device Tree Selftest > +----------------------------------- > + > +Author: Gaurav Minocha <gaurav.minocha.os@xxxxxxxxx> > + > +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; > + struct device_node *allnext; /* next in list of all nodes */ > + ... > + }; > + > +Figure 1, describes a generic structure of machineâ??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, sibling4â??s > +parent points to root node) > + > +root (â??/â??) > + | > +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 > + > + > +*allnext: it is used to link all the nodes of DT into a list. So, for the > + above tree the list would be as follows: > + > +root->child1->child11->sibling12->sibling13->child131->sibling14->sibling2-> > +child21->sibling22->sibling23->sibling3->child31->sibling32->sibling4->null > + > +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_device_tree() to unflatten the flattened > +blob. And finally, if the machineâ??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 (â??/â??) > + | > + testcase-data > + | > + test-child0 -> test-sibling1 -> test-sibling2 -> test-sibling3 -> null > + | | | | > + test-child01 null null null > + > + > +allnext list: > + > +root->testcase-data->test-child0->test-child01->test-sibling1->test-sibling2 > +->test-sibling3->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 isnâ??t > +required to attach the root(â??/â??) 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 (â??/â??) > + | > +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 (â??/â??) > + | > +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 isnâ??t attached rather its > +properties are updated to the live treeâ??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() first updates all_next linked list, by > +attaching the previous nodeâ??s allnext to current nodeâ??s allnext pointer. And > +then, it either updates the child pointer of given nodeâ??s parent to its > +sibling or attaches the previous sibling to the given nodeâ??s sibling, as > +appropriate. That is it :) > -- > 1.7.9.5 > -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
