dtc: Flexible tree checking infrastructure (v2)

dtc: Flexible tree checking infrastructure

Here, at last, is a substantial start on revising dtc's infrastructure
for checking the tree; this is the rework I've been saying was
necessary practically since dtc was first release.

In the new model, we have a table of "check" structures, each with a
name, references to checking functions, and status variables.  Each
check can (in principle) be individually switched off or on (as either
a warning or error).  Checks have a list of prerequisites, so if
checks need to rely on results from earlier checks to make sense (or
even to avoid crashing) they just need to list the relevant other
checks there.

For now, only the "structural" checks and the fixups for phandle
references are converted to the new mechanism.  The rather more
involved semantic checks (which is where this new mechanism will
really be useful) will have to be converted in future patches.

At present, there's no user interface for turning on/off the checks -
the -f option now forces output even if "error" level checks fail.
Again, future patches will be needed to add the fine-grained control,
but that should be quite straightforward with the infrastructure
implemented here.

Also adds a testcase for the handling of bad references, which catches
a bug encountered while developing this patch.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>

tests/run_tests.sh

@@ -157,6 +157,8 @@ dtc_tests () {
     run_test dtc-checkfails.sh -I dts -O dtb dup-phandle.dts
     run_test dtc-checkfails.sh -I dts -O dtb zero-phandle.dts
     run_test dtc-checkfails.sh -I dts -O dtb minusone-phandle.dts
+    run_test dtc-checkfails.sh -I dts -O dtb nonexist-node-ref.dts
+    run_test dtc-checkfails.sh -I dts -O dtb nonexist-label-ref.dts
 }
 
 while getopts "vt:m" ARG ; do