Pfthb

I am a yocto noob, trying to decipher how the device tree is built from a Xilinx hardware definition (.hdf) file. But my question is more general.

Is there a yocto way to find the source of task?
Given a task name is it possible to find where the tasks source code lives? (presumably in a recipe or class)

As an example, where is the source for the Python task do_create_yaml which is called by recipes in the meta-xilinx-bsp layer that compile the device tree blob?

bitbake -e device-tree

Will dump the python source for do_create_yaml (amongst the rest of it prodigious output) but how can I find where that is coming from?

Device tree is part of Linux Kernel. In Yocto, this is compiled from KERNEL_DEVICETREE variable value either defined as part of Linux Kernel recipe or machine configuration.

For example, for cubieboard7 as defined here,

KERNEL_DEVICETREE = "s700_cb7_linux.dtb"

instructs the compilation to use this dts file for compilation. This is done by yocto by using various classes.

In our example, we inherit kernel.bbclass which in turn inherits kernel-devicetree.bbclass, in this class (copied from kernel-devicetree.bbclass),

do_compile_append() 
 for dtbf in $KERNEL_DEVICETREE; do
 dtb=`normalize_dtb "$dtbf"`
 oe_runmake $dtb
 done


do_install_append() 
 for dtbf in $KERNEL_DEVICETREE; do
 dtb=`normalize_dtb "$dtbf"`
 dtb_ext=$dtb##*.
 dtb_base_name=`basename $dtb .$dtb_ext`
 dtb_path=`get_real_dtb_path_in_kernel "$dtb"`
 install -m 0644 $dtb_path $D/$KERNEL_IMAGEDEST/$dtb_base_name.$dtb_ext
 done


do_deploy_append() {
 for dtbf in $KERNEL_DEVICETREE; do
 dtb=`normalize_dtb "$dtbf"`

this appends tasks to compile, install and deploy tasks. So defining KERNEL_DEVICETREE enables the automatic build of dtb.

I found that the datastore contains the filename for tasks as a VarFlag,
from a devpyshell

pydevshell> d.getVarFlags("do_create_yaml")

gives

'filename': '.....yocto/sources/core/../meta-xilinx-tools/classes/xsctyaml.bbclass', 'lineno': '61', 'func': 1, 'task': 1, 'python': '1', 'deps': ['do_prepare_recipe_sysroot']

So for the example in my question the active definition for the do_create_yaml task is in xsctyaml.bbclass.