edid: allow arbitrary-length checksums

Some of the EDID extensions like DisplayID do checksums of their
subsections. Currently checksums can be only applied to the whole
extension blocks which are 128 bytes.

This patch allows to checksum arbitrary parts of EDID, and not only
whole extension blocks.

Based-on: <20210303152948.59943-2-akihiko.odaki@gmail.com>
Signed-off-by: Konstantin Nazarov <mail@knazarov.com>
Message-Id: <20210315114639.91953-2-mail@knazarov.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Message-id: 20210427150824.638359-1-kraxel@redhat.com
Message-Id: <20210427150824.638359-8-kraxel@redhat.com>

diff --git a/hw/display/edid-generate.c b/hw/display/edid-generate.c
index b70ab1557e509d5b5a8aecf2472035c9e5178075..bdd01571fc9b3e01c182980c7d4db41155e9522a 100644 (file)
--- a/hw/display/edid-generate.c
+++ b/hw/display/edid-generate.c
@@ -159,17 +159,17 @@ static void edid_fill_modes(uint8_t *edid, uint8_t *xtra3, uint8_t *dta,
     }
 }
 
-static void edid_checksum(uint8_t *edid)
+static void edid_checksum(uint8_t *edid, size_t len)
 {
     uint32_t sum = 0;
     int i;
 
-    for (i = 0; i < 127; i++) {
+    for (i = 0; i < len; i++) {
         sum += edid[i];
     }
     sum &= 0xff;
     if (sum) {
-        edid[127] = 0x100 - sum;
+        edid[len] = 0x100 - sum;
     }
 }
 
@@ -474,9 +474,9 @@ void qemu_edid_generate(uint8_t *edid, size_t size,
 
     /* =============== finish up =============== */
 
-    edid_checksum(edid);
+    edid_checksum(edid, 127);
     if (dta) {
-        edid_checksum(dta);
+        edid_checksum(dta, 127);
     }
 }