util/mediatek: Add check-pi-img.py

According to MediaTek's proprietary PI_IMG parser, two cookies (one
header and one footer) are expected. Therefore, add a script to perform
validity check of the PI_IMG firmware, so that format errors could be
caught in build time.

Change-Id: I27011492c7fab747aa3ee12d514d20a6a52d0a4d
Signed-off-by: Yu-Ping Wu <yupingso@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87226
Reviewed-by: Yidi Lin <yidilin@google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

Documentation/util.md

@@ -88,6 +88,7 @@ image for testing purposes and for working on firmware. `Bash`
 * __[me_cleaner](https://github.com/corna/me_cleaner)__ - Tool for
 partial deblobbing of Intel ME/TXE firmware images `Python`
 * __mediatek__
+	* check-pi-img.py - Check `PI_IMG` firmware. `Python3`
 	* gen-bl-img.py - Generate MediaTek bootloader header.
 `Python3`
 * __mma__ - Memory Margin Analysis automation tests `Bash`

util/README.md

@@ -79,6 +79,7 @@ image for testing purposes and for working on firmware. `Bash`
 * __[me_cleaner](https://github.com/corna/me_cleaner)__ - Tool for
 partial deblobbing of Intel ME/TXE firmware images `Python`
 * __mediatek__
+	* check-pi-img.py - Check `PI_IMG` firmware. `Python3`
 	* gen-bl-img.py - Generate MediaTek bootloader header.
 `Python3`
 * __mma__ - Memory Margin Analysis automation tests `Bash`

util/mediatek/check-pi-img.py

@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+#
+# SPDX-License-Identifier: GPL-2.0-only
+
+import argparse
+
+
+HEADER_OFFSET = 0x200
+COOKIE = 0x17C3A6B4
+
+
+def check_pi_img(pi_img):
+    cookie_count = 0
+    with open(pi_img, "rb") as f:
+        f.seek(HEADER_OFFSET)
+        while True:
+            data = f.read(4)
+            if not data:
+                break
+            value = int.from_bytes(data, byteorder="little", signed=False)
+            if value == COOKIE:
+                cookie_count += 1
+    if cookie_count != 2:
+        raise ValueError("Invalid PI_IMG {} (expected 2 cookies; found {})"
+                         .format(pi_img, cookie_count))
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("pi_img")
+    args = parser.parse_args()
+    check_pi_img(args.pi_img)
+
+if __name__ == '__main__':
+    main()

util/mediatek/description.md

@@ -1,2 +1,3 @@
 __mediatek__
+  * check-pi-img.py - Check `PI_IMG` firmware. `Python3`
   * gen-bl-img.py - Generate MediaTek bootloader header. `Python3`