display/edid: add qemu_edid_size()

Helper function to figure the size of a edid blob, by checking how many
extensions are present.  Both the base edid blob and the extensions are
128 bytes in size.
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Message-id: 20180925075646.25114-3-kraxel@redhat.com

hw/display/edid-generate.c

@@ -423,3 +423,17 @@ void qemu_edid_generate(uint8_t *edid, size_t size,
         edid_checksum(dta);
     }
 }
+
+size_t qemu_edid_size(uint8_t *edid)
+{
+    uint32_t exts;
+
+    if (edid[0] != 0x00 ||
+        edid[1] != 0xff) {
+        /* doesn't look like a valid edid block */
+        return 0;
+    }
+
+    exts = edid[126];
+    return 128 * (exts + 1);
+}

include/hw/display/edid.h

@@ -14,5 +14,6 @@ typedef struct qemu_edid_info {
 
 void qemu_edid_generate(uint8_t *edid, size_t size,
                         qemu_edid_info *info);
+size_t qemu_edid_size(uint8_t *edid);
 
 #endif /* EDID_H */