drm/edid: add HF-EEODB support to EDID read and allocation

HDMI 2.1 section 10.3.6 defines an HDMI Forum EDID Extension Override
Data Block, which may contain a different extension count than the base
block claims. Add support for reading more EDID data if available. The
extra blocks aren't parsed yet, though.

Hard-coding the EEODB parsing instead of using the iterators we have is
a bit of a bummer, but we have to be able to do this on a partially
allocated EDID while reading it.

v2:
- Check for CEA Data Block Collection size (Ville)
- Amend commit message and comment about hard-coded parsing

Signed-off-by: Jani Nikula <[e-mail]>
Reviewed-by: Ville Syrjälä <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/57b[e-mail]

drivers/gpu/drm/drm_edid.c

···
 		(edid->version == version && edid->revision > revision);
 }
 
+static int edid_hfeeodb_extension_block_count(const struct edid *edid);
+
+static int edid_hfeeodb_block_count(const struct edid *edid)
+{
+	int eeodb = edid_hfeeodb_extension_block_count(edid);
+
+	return eeodb ? eeodb + 1 : 0;
+}
+
 static int edid_extension_block_count(const struct edid *edid)
 {
 	return edid->extensions;
···
 	struct edid *new;
 	int i, valid_blocks = 0;
 
+	/*
+	 * Note: If the EDID uses HF-EEODB, but has invalid blocks, we'll revert
+	 * back to regular extension count here. We don't want to start
+	 * modifying the HF-EEODB extension too.
+	 */
 	for (i = 0; i < edid_block_count(edid); i++) {
 		const void *src_block = edid_block_data(edid, i);
 
···
 				     size_t *size)
 {
 	enum edid_block_status status;
-	int i, invalid_blocks = 0;
+	int i, num_blocks, invalid_blocks = 0;
 	struct edid *edid, *new;
 	size_t alloc_size = EDID_LENGTH;
 
···
 		goto fail;
 	edid = new;
 
-	for (i = 1; i < edid_block_count(edid); i++) {
+	num_blocks = edid_block_count(edid);
+	for (i = 1; i < num_blocks; i++) {
 		void *block = (void *)edid_block_data(edid, i);
 
 		status = edid_block_read(block, i, read_block, context);
···
 			if (status == EDID_BLOCK_READ_FAIL)
 				goto fail;
 			invalid_blocks++;
+		} else if (i == 1) {
+			/*
+			 * If the first EDID extension is a CTA extension, and
+			 * the first Data Block is HF-EEODB, override the
+			 * extension block count.
+			 *
+			 * Note: HF-EEODB could specify a smaller extension
+			 * count too, but we can't risk allocating a smaller
+			 * amount.
+			 */
+			int eeodb = edid_hfeeodb_block_count(edid);
+
+			if (eeodb > num_blocks) {
+				num_blocks = eeodb;
+				alloc_size = edid_size_by_blocks(num_blocks);
+				new = krealloc(edid, alloc_size, GFP_KERNEL);
+				if (!new)
+					goto fail;
+				edid = new;
+			}
 		}
 	}
 
 	if (invalid_blocks) {
-		connector_bad_edid(connector, edid, edid_block_count(edid));
+		connector_bad_edid(connector, edid, num_blocks);
 
 		edid = edid_filter_invalid_blocks(edid, &alloc_size);
 	}
···
 #define CTA_EXT_DB_HDR_STATIC_METADATA	6
 #define CTA_EXT_DB_420_VIDEO_DATA	14
 #define CTA_EXT_DB_420_VIDEO_CAP_MAP	15
+#define CTA_EXT_DB_HF_EEODB		0x78
 #define CTA_EXT_DB_HF_SCDB		0x79
 
 #define EDID_BASIC_AUDIO	(1 << 6)
···
 		cea_db_payload_len(db) >= 7;
 }
 
+static bool cea_db_is_hdmi_forum_eeodb(const void *db)
+{
+	return cea_db_is_extended_tag(db, CTA_EXT_DB_HF_EEODB) &&
+		cea_db_payload_len(db) >= 2;
+}
+
 static bool cea_db_is_microsoft_vsdb(const struct cea_db *db)
 {
 	return cea_db_is_vendor(db, MICROSOFT_IEEE_OUI) &&
···
 {
 	return cea_db_is_extended_tag(db, CTA_EXT_DB_HDR_STATIC_METADATA) &&
 		cea_db_payload_len(db) >= 3;
+}
+
+/*
+ * Get the HF-EEODB override extension block count from EDID.
+ *
+ * The passed in EDID may be partially read, as long as it has at least two
+ * blocks (base block and one extension block) if EDID extension count is > 0.
+ *
+ * Note that this is *not* how you should parse CTA Data Blocks in general; this
+ * is only to handle partially read EDIDs. Normally, use the CTA Data Block
+ * iterators instead.
+ *
+ * References:
+ * - HDMI 2.1 section 10.3.6 HDMI Forum EDID Extension Override Data Block
+ */
+static int edid_hfeeodb_extension_block_count(const struct edid *edid)
+{
+	const u8 *cta;
+
+	/* No extensions according to base block, no HF-EEODB. */
+	if (!edid_extension_block_count(edid))
+		return 0;
+
+	/* HF-EEODB is always in the first EDID extension block only */
+	cta = edid_extension_block_data(edid, 0);
+	if (edid_block_tag(cta) != CEA_EXT || cea_revision(cta) < 3)
+		return 0;
+
+	/* Need to have the data block collection, and at least 3 bytes. */
+	if (cea_db_collection_size(cta) < 3)
+		return 0;
+
+	/*
+	 * Sinks that include the HF-EEODB in their E-EDID shall include one and
+	 * only one instance of the HF-EEODB in the E-EDID, occupying bytes 4
+	 * through 6 of Block 1 of the E-EDID.
+	 */
+	if (!cea_db_is_hdmi_forum_eeodb(&cta[4]))
+		return 0;
+
+	return cta[4 + 2];
 }
 
 static void drm_parse_y420cmdb_bitmap(struct drm_connector *connector,