On 9/8/2014 6:20 AM, Grant Likely wrote: > 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. Is it ok to use UTF-8 characters outside the ascii range in Documentation .txt files? If not, there are a few below (I'll point out at least a few inline). The characters are all various forms of a quote or apostrophe. I do not know what the characters in this reply will look like in anyone else's email client. In thunderbird, the non-ascii UTF-8 characters in the original patch displayed properly. In thunderbird, the same text in Grant's reply, prefixed with '> ' to indicate an email reply the non-ascii UTF-8 is mangled. In thunderbird, if I reply to Grant's reply, the same mangling occurs. -Frank > > 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 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 ^^^ non-ascii UTF-8 >> +parent points to root node) >> + >> +root (‘/’) ^^^ ^^^ non-ascii UTF-8 >> + | >> +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 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 (‘/’) ^^^ ^^^ non-ascii UTF-8 >> + | >> + 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 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 (‘/’) ^^^ ^^^ non-ascii UTF-8 >> + | >> +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 (‘/’) ^^^ ^^^ non-ascii UTF-8 >> + | >> +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 ^^^ non-ascii UTF-8 >> +properties are updated to the live tree’s node by calling the function ^^^ non-ascii UTF-8 >> +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 node’s allnext to current node’s allnext pointer. And ^^^ ^^^ non-ascii UTF-8 non-ascii UTF-8 >> +then, it either updates the child pointer of given node’s parent to its ^^^ non-ascii UTF-8 >> +sibling or attaches the previous sibling to the given node’s sibling, as ^^^ non-ascii UTF-8 >> +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 > -- 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
