drm/edid: parse CEA blocks embedded in DisplayID

DisplayID blocks allow embedding of CEA blocks. The payloads are
identical to traditional top level CEA extension blocks, but the header
is slightly different.

This change allows the CEA parser to find a CEA block inside a DisplayID
block. Additionally, it adds support for parsing the embedded CTA
header. No further changes are necessary due to payload parity.

This change fixes audio support for the Valve Index HMD.
Signed-off-by: Andres Rodriguez <andresx7@gmail.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: <stable@vger.kernel.org> # v4.15
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619180901.17901-1-andresx7@gmail.com

drivers/gpu/drm/drm_edid.c

@@ -1342,6 +1342,7 @@ MODULE_PARM_DESC(edid_fixup,
 
 static void drm_get_displayid(struct drm_connector *connector,
 			      struct edid *edid);
+static int validate_displayid(u8 *displayid, int length, int idx);
 
 static int drm_edid_block_checksum(const u8 *raw_edid)
 {
@@ -2926,16 +2927,46 @@ static u8 *drm_find_edid_extension(const struct edid *edid, int ext_id)
 	return edid_ext;
 }
 
-static u8 *drm_find_cea_extension(const struct edid *edid)
-{
-	return drm_find_edid_extension(edid, CEA_EXT);
-}
 
 static u8 *drm_find_displayid_extension(const struct edid *edid)
 {
 	return drm_find_edid_extension(edid, DISPLAYID_EXT);
 }
 
+static u8 *drm_find_cea_extension(const struct edid *edid)
+{
+	int ret;
+	int idx = 1;
+	int length = EDID_LENGTH;
+	struct displayid_block *block;
+	u8 *cea;
+	u8 *displayid;
+
+	/* Look for a top level CEA extension block */
+	cea = drm_find_edid_extension(edid, CEA_EXT);
+	if (cea)
+		return cea;
+
+	/* CEA blocks can also be found embedded in a DisplayID block */
+	displayid = drm_find_displayid_extension(edid);
+	if (!displayid)
+		return NULL;
+
+	ret = validate_displayid(displayid, length, idx);
+	if (ret)
+		return NULL;
+
+	idx += sizeof(struct displayid_hdr);
+	for_each_displayid_db(displayid, block, idx, length) {
+		if (block->tag == DATA_BLOCK_CTA) {
+			cea = (u8 *)block;
+			break;
+		}
+	}
+
+	return cea;
+}
+
 /*
  * Calculate the alternate clock for the CEA mode
  * (60Hz vs. 59.94Hz etc.)
@@ -3659,6 +3690,27 @@ cea_revision(const u8 *cea)
 static int
 cea_db_offsets(const u8 *cea, int *start, int *end)
 {
+	/* DisplayID CTA extension blocks and top-level CEA EDID
+	 * block header definitions differ in the following bytes:
+	 *   1) Byte 2 of the header specifies length differently,
+	 *   2) Byte 3 is only present in the CEA top level block.
+	 *
+	 * The different definitions for byte 2 follow.
+	 *
+	 * DisplayID CTA extension block defines byte 2 as:
+	 *   Number of payload bytes
+	 *
+	 * CEA EDID block defines byte 2 as:
+	 *   Byte number (decimal) within this block where the 18-byte
+	 *   DTDs begin. If no non-DTD data is present in this extension
+	 *   block, the value should be set to 04h (the byte after next).
+	 *   If set to 00h, there are no DTDs present in this block and
+	 *   no non-DTD data.
+	 */
+	if (cea[0] == DATA_BLOCK_CTA) {
+		*start = 3;
+		*end = *start + cea[2];
+	} else if (cea[0] == CEA_EXT) {
 		/* Data block offset in CEA extension block */
 		*start = 4;
 		*end = cea[2];
@@ -3666,6 +3718,10 @@ cea_db_offsets(const u8 *cea, int *start, int *end)
 			*end = 127;
 		if (*end < 4 || *end > 127)
 			return -ERANGE;
+	} else {
+		return -ENOTSUPP;
+	}
+
 	return 0;
 }
 
@@ -5406,6 +5462,9 @@ static int drm_parse_display_id(struct drm_connector *connector,
 		case DATA_BLOCK_TYPE_1_DETAILED_TIMING:
 			/* handled in mode gathering code. */
 			break;
+		case DATA_BLOCK_CTA:
+			/* handled in the cea parser code. */
+			break;
 		default:
 			DRM_DEBUG_KMS("found DisplayID tag 0x%x, unhandled\n", block->tag);
 			break;

include/drm/drm_displayid.h

@@ -40,6 +40,7 @@
 #define DATA_BLOCK_DISPLAY_INTERFACE 0x0f
 #define DATA_BLOCK_STEREO_DISPLAY_INTERFACE 0x10
 #define DATA_BLOCK_TILED_DISPLAY 0x12
+#define DATA_BLOCK_CTA 0x81
 
 #define DATA_BLOCK_VENDOR_SPECIFIC 0x7f
 
@@ -90,4 +91,13 @@ struct displayid_detailed_timing_block {
 	struct displayid_block base;
 	struct displayid_detailed_timings_1 timings[0];
 };
+
+#define for_each_displayid_db(displayid, block, idx, length) \
+	for ((block) = (struct displayid_block *)&(displayid)[idx]; \
+	     (idx) + sizeof(struct displayid_block) <= (length) && \
+	     (idx) + sizeof(struct displayid_block) + (block)->num_bytes <= (length) && \
+	     (block)->num_bytes > 0; \
+	     (idx) += (block)->num_bytes + sizeof(struct displayid_block), \
+	     (block) = (struct displayid_block *)&(displayid)[idx])
+
 #endif