scripts/make_fit: Support an initial ramdisk

FIT (Flat Image Tree) allows a ramdisk to be included in each
configuration. Add support for this to the script.

This feature is not available via 'make image.fit' since the ramdisk
likely needs to be built separately anyway, e.g. using modules from
the kernel build. Future work may provide support for doing that.

Note that the uncompressed size is not correct when a ramdisk is used,
since it is too expensive to decompress the ramdisk.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Nicolas Schier <nsc@kernel.org>
Reviewed-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://patch.msgid.link/20260106162738.2605574-3-sjg@chromium.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

scripts/make_fit.py

@@ -10,10 +10,14 @@
 Usage:
     make_fit.py -A arm64 -n 'Linux-6.6' -O linux
         -o arch/arm64/boot/image.fit -k /tmp/kern/arch/arm64/boot/image.itk
-        @arch/arm64/boot/dts/dtbs-list -E -c gzip
+        -r /boot/initrd.img-6.14.0-27-generic @arch/arm64/boot/dts/dtbs-list
+        -E -c gzip
 
-Creates a FIT containing the supplied kernel and a set of devicetree files,
-either specified individually or listed in a file (with an '@' prefix).
+Creates a FIT containing the supplied kernel, an optional ramdisk, and a set of
+devicetree files, either specified individually or listed in a file (with an
+'@' prefix).
+
+Use -r to specify an existing ramdisk/initrd file.
 
 Use -E to generate an external FIT (where the data is placed after the
 FIT data structure). This allows parsing of the data without loading
@@ -29,8 +33,6 @@ looks at the .cmd files produced by the kernel build.
 
 The resulting FIT can be booted by bootloaders which support FIT, such
 as U-Boot, Linuxboot, Tianocore, etc.
-
-Note that this tool does not yet support adding a ramdisk / initrd.
 """
 
 import argparse
@@ -81,6 +83,8 @@ def parse_args():
           help='Specifies the operating system')
     parser.add_argument('-k', '--kernel', type=str, required=True,
           help='Specifies the (uncompressed) kernel input file (.itk)')
+    parser.add_argument('-r', '--ramdisk', type=str,
+          help='Specifies the ramdisk/initrd input file')
     parser.add_argument('-v', '--verbose', action='store_true',
                         help='Enable verbose output')
     parser.add_argument('dtbs', type=str, nargs='*',
@@ -133,7 +137,28 @@ def write_kernel(fsw, data, args):
         fsw.property_u32('entry', 0)
 
 
-def finish_fit(fsw, entries):
+def write_ramdisk(fsw, data, args):
+    """Write out the ramdisk image
+
+    Writes a ramdisk node along with the required properties
+
+    Args:
+        fsw (libfdt.FdtSw): Object to use for writing
+        data (bytes): Data to write (possibly compressed)
+        args (Namespace): Contains necessary strings:
+            arch: FIT architecture, e.g. 'arm64'
+            fit_os: Operating Systems, e.g. 'linux'
+    """
+    with fsw.add_node('ramdisk'):
+        fsw.property_string('description', 'Ramdisk')
+        fsw.property_string('type', 'ramdisk')
+        fsw.property_string('arch', args.arch)
+        fsw.property_string('compression', 'none')
+        fsw.property_string('os', args.os)
+        fsw.property('data', data)
+
+
+def finish_fit(fsw, entries, has_ramdisk=False):
     """Finish the FIT ready for use
 
     Writes the /configurations node and subnodes
@@ -143,6 +168,7 @@ def finish_fit(fsw, entries):
         entries (list of tuple): List of configurations:
             str: Description of model
             str: Compatible stringlist
+        has_ramdisk (bool): True if a ramdisk is included in the FIT
     """
     fsw.end_node()
     seq = 0
@@ -154,6 +180,8 @@ def finish_fit(fsw, entries):
                 fsw.property_string('description', model)
                 fsw.property('fdt', bytes(''.join(f'fdt-{x}\x00' for x in files), "ascii"))
                 fsw.property_string('kernel', 'kernel')
+                if has_ramdisk:
+                    fsw.property_string('ramdisk', 'ramdisk')
     fsw.end_node()
 
 
@@ -274,6 +302,14 @@ def build_fit(args):
     size += os.path.getsize(args.kernel)
     write_kernel(fsw, comp_data, args)
 
+    # Handle the ramdisk if provided. Compression is not supported as it is
+    # already compressed.
+    if args.ramdisk:
+        with open(args.ramdisk, 'rb') as inf:
+            data = inf.read()
+        size += len(data)
+        write_ramdisk(fsw, data, args)
+
     for fname in args.dtbs:
         # Ignore non-DTB (*.dtb) files
         if os.path.splitext(fname)[1] != '.dtb':
@@ -296,12 +332,12 @@ def build_fit(args):
 
         entries.append([model, compat, files_seq])
 
-    finish_fit(fsw, entries)
+    finish_fit(fsw, entries, bool(args.ramdisk))
 
     # Include the kernel itself in the returned file count
     fdt = fsw.as_fdt()
     fdt.pack()
-    return fdt.as_bytearray(), seq + 1, size
+    return fdt.as_bytearray(), seq + 1 + bool(args.ramdisk), size
 
 
 def run_make_fit():