From ba5df47c97428c1396b4233a28bcbb7bd1d37b69 Mon Sep 17 00:00:00 2001
From: Maxim Devaev <mdevaev@gmail.com>
Date: Wed, 12 Mar 2025 23:00:33 +0200
Subject: [PATCH] edidconf: Allow 128-byte edids for --import-display-ids

---
 kvmd/apps/edidconf/__init__.py |  2 +-
 kvmd/edid.py                   | 25 +++++++++++++++++--------
 2 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/kvmd/apps/edidconf/__init__.py b/kvmd/apps/edidconf/__init__.py
index 2234b5a8..717f9e32 100644
--- a/kvmd/apps/edidconf/__init__.py
+++ b/kvmd/apps/edidconf/__init__.py
@@ -71,7 +71,7 @@ def _read_out2_edid() -> (Edid | None):
         data = file.read()
         if len(data) == 0:
             return None
-    return Edid.from_file(os.path.join(path, "edid"))
+    return Edid.from_file(os.path.join(path, "edid"), allow_short=True)
 
 
 def _adopt_out2_ids(dest: Edid) -> None:
diff --git a/kvmd/edid.py b/kvmd/edid.py
index bfa62e3c..8532a06b 100644
--- a/kvmd/edid.py
+++ b/kvmd/edid.py
@@ -69,6 +69,9 @@ class _CeaBlock:
         return _CeaBlock(tag, data)
 
 
+_LONG = 256
+_SHORT = 128
+
 _CEA = 128
 _CEA_AUDIO = 1
 _CEA_SPEAKERS = 4
@@ -77,12 +80,18 @@ _CEA_SPEAKERS = 4
 class Edid:
     # https://en.wikipedia.org/wiki/Extended_Display_Identification_Data
 
-    def __init__(self, data: bytes) -> None:
-        assert len(data) == 256
+    def __init__(self, data: bytes, allow_short: bool=False) -> None:
+        if allow_short:
+            assert len(data) in [_SHORT, _LONG], f"Invalid EDID length: {len(data)}, should be {_SHORT} or {_LONG} bytes"
+        else:
+            assert len(data) == _LONG, f"Invalid EDID length: {len(data)}, should be {_LONG} bytes"
+            assert data[126] == 1, "Zero extensions number"
+            assert (data[_CEA + 0], data[_CEA + 1]) == (0x02, 0x03), "Can't find CEA extension"
         self.__data = list(data)
+        self.__long = (len(data) == _LONG)
 
     @classmethod
-    def from_file(cls, path: str) -> "Edid":
+    def from_file(cls, path: str, allow_short: bool=False) -> "Edid":
         with _smart_open(path, "rb") as file:
             data = file.read()
             if not data.startswith(b"\x00\xFF\xFF\xFF\xFF\xFF\xFF\x00"):
@@ -91,10 +100,7 @@ class Edid:
                     int(text[index:index + 2], 16)
                     for index in range(0, len(text), 2)
                 ])
-            assert len(data) == 256, f"Invalid EDID length: {len(data)}, should be 256 bytes"
-            assert data[126] == 1, "Zero extensions number"
-            assert (data[_CEA + 0], data[_CEA + 1]) == (0x02, 0x03), "Can't find CEA extension"
-        return Edid(data)
+        return Edid(data, allow_short)
 
     def write_hex(self, path: str) -> None:
         self.__update_checksums()
@@ -115,7 +121,8 @@ class Edid:
 
     def __update_checksums(self) -> None:
         self.__data[127] = 256 - (sum(self.__data[:127]) % 256)
-        self.__data[255] = 256 - (sum(self.__data[128:255]) % 256)
+        if self.__long:
+            self.__data[255] = 256 - (sum(self.__data[128:255]) % 256)
 
     # =====
 
@@ -229,6 +236,8 @@ class Edid:
             self.__data[_CEA + 3] &= (0xFF - 0b01000000)  # ~X
 
     def __parse_cea(self) -> tuple[list[_CeaBlock], bytes]:
+        assert self.__long, "This EDID does not contain any CEA blocks"
+
         cea = self.__data[_CEA:]
         dtd_begin = cea[2]
         if dtd_begin == 0: