scripts: add cameo image header generator

The cameo header is a 0x40-byte header used by D-Link DGS 1210 switches
and Apresia ApresiaLightGS series. cameo-imghdr.py is a clean-room
reimplementation of imghdr present in the DGS-1210-28-GPL package.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
[fix board_version argument's help text]
Signed-off-by: Sander Vanheule <sander@svanheule.net>

scripts/cameo-imghdr.py

@@ -0,0 +1,86 @@
+#!/usr/bin/python3
+# SPDX-License-Identifier: GPL-2.0-or-later
+#
+# Copyright (C) 2022 Luiz Angelo Daros de Luca <luizluca@gmail.com>
+#
+# Cameo Image header geneator, used by some D-Link DGS-1210 switches
+# and APRESIA ApresiaLightGS series
+#
+import argparse
+import pathlib
+import socket
+import struct
+
+MODEL_LEN = 20
+SIGNATURE_LEN = 16
+LINUXLOAD_LEN = 10
+BUFSIZE = 4096
+
+parser = argparse.ArgumentParser(description='Generate Cameo firmware header.')
+parser.add_argument('source_file', type=argparse.FileType('rb'))
+parser.add_argument('dest_file', type=argparse.FileType('wb'))
+parser.add_argument('model')
+parser.add_argument('signature')
+parser.add_argument('partition', type=int, choices=range(0,10),
+                    metavar="partition=[0-9]",help="partition id")
+parser.add_argument('customer_signature', type=int, choices=range(0,10),
+                    metavar="customer_signature=[0-9]",
+                    help="customer signature")
+parser.add_argument('board_version', type=int, choices=range(0,2**32),
+                    metavar="board_version=[0-4294967295]",
+                    help="board version")
+parser.add_argument('linux_loadaddr', nargs='?',
+                    help="Kernel start address in 0xFFFFFFFF format")
+args = parser.parse_args()
+
+if len(args.model) > MODEL_LEN:
+    raise ValueError(f"Model '{args.model}' is greater than {MODEL_LEN} bytes")
+
+if len(args.signature) > SIGNATURE_LEN:
+    raise ValueError(f"Signature '{args.signature}' is greater than"
+                     f"{SIGNATURE_LEN} bytes")
+
+if args.signature == "os":
+    if args.linux_loadaddr:
+        if len(args.linux_loadaddr) > LINUXLOAD_LEN:
+            raise ValueError(f"linux_loadaddr '{args.linux_loadaddr}' is greater"
+                             f"than {LINUXLOAD_LEN} bytes")
+        if (args.linux_loadaddr[0:2] != "0x"):
+            raise ValueError(f"linux_loadaddr '{args.linux_loadaddr}' must use"
+                             f"the 0x789ABCDE format")
+        int(args.linux_loadaddr[2:],16)
+    else:
+        raise ValueError(f"linux_loadaddr is required for signature 'os'")
+else:
+    args.linux_loadaddr = ""
+
+checksum = 0
+size = 0
+while True:
+    buf = args.source_file.read(BUFSIZE)
+    if not buf:
+        break
+    checksum = sum(iter(buf),checksum) % (1<<32)
+    size += len(buf)
+
+args.dest_file.write(struct.pack('!I', checksum))
+args.dest_file.write(struct.pack(f'{MODEL_LEN}s',
+                                 args.model.encode("ascii")))
+args.dest_file.write(struct.pack(f'{SIGNATURE_LEN}s',
+                                 args.signature.encode("ascii")))
+args.dest_file.write(struct.pack('!B', args.partition))
+args.dest_file.write(struct.pack('!B', 0x40)) # ??? This header size?
+args.dest_file.write(struct.pack('!B', 0x00)) # ??? Encrypted?
+args.dest_file.write(struct.pack('!B', args.customer_signature))
+args.dest_file.write(struct.pack('!I', args.board_version))
+args.dest_file.write(struct.pack('!I', size))
+args.dest_file.write(struct.pack(f'{LINUXLOAD_LEN}s',
+                                 args.linux_loadaddr.encode("ascii")))
+args.dest_file.write(struct.pack('!2x'))
+
+args.source_file.seek(0)
+while True:
+    buf = args.source_file.read(BUFSIZE)
+    if not buf:
+        break
+    args.dest_file.write(buf)