lib: add dtbutils library module

with a function for concatenating DTBOs onto DTBs.

Signed-off-by: Matt Madison <matt@madison.systems>

lib/oe4t/__init__.py

@@ -0,0 +1,4 @@
+from pkgutil import extend_path
+__path__ = extend_path(__path__, __name__)
+
+BBIMPORTS = ["dtbutils"]

lib/oe4t/dtbutils.py

@@ -0,0 +1,49 @@
+def concat_dtb_overlays(dtbfile, overlays, outfile, d):
+    """
+    Produce an output DTB file that has zero or more
+    overlay DTBs concatenated to it, for processing by
+    NVIDIA's OverlayManager UEFI driver.
+
+    Source DTB and overlay files can reside either under
+    ${EXTERNAL_KERNEL_DEVICETREE} or in ${DEPLOY_DIR_IMAGE}.
+
+    dtbfile: Main DTB file
+    overlays: space-separated list of zero or more DTBO files
+    outfile: name of output file
+    d: recipe context
+    """
+    import os
+    import bb.utils
+
+    def find_file_under(fname, rootdir):
+        for dirname, _, f in os.walk(rootdir):
+            if fname in f:
+                return os.path.join(dirname, fname)
+        return None
+
+    def locate_dtb_files(dtbnames):
+        result = []
+        extern_root = d.getVar('EXTERNAL_KERNEL_DEVICETREE')
+        imgdeploydir = d.getVar('DEPLOY_DIR_IMAGE')
+        for dtb in dtbnames:
+            if os.path.isabs(dtb):
+                result.append(dtb)
+                continue
+            if extern_root:
+                dtbpath = find_file_under(dtb, extern_root)
+                if dtbpath:
+                    result.append(dtbpath)
+                    continue
+            result.append(os.path.join(imgdeploydir, dtb))
+        return result
+
+    infiles = locate_dtb_files([dtbfile] + overlays.split())
+    bb.note("Creating concatenated device tree: ", outfile)
+    with open(outfile, "wb") as outf:
+        for infile in infiles:
+            # the overlay manager expects all DTBOs to start
+            # on a 4K page boundary
+            outf.write(bytearray(int((outf.tell() + 4095) / 4096) * 4096))
+            bb.note("    Adding:  ", infile)
+            with open(infile, "rb") as inf:
+                outf.write(inf.read())