1 files changed, 70 insertions, 0 deletions
diff --git a/include/media/cec.h b/include/media/cec.h
index df6b3bd31284..b7339cc6fd3d 100644
--- a/include/media/cec.h
+++ b/include/media/cec.h
@@ -435,4 +435,74 @@ static inline void cec_phys_addr_invalidate(struct cec_adapter *adap)
 	cec_s_phys_addr(adap, CEC_PHYS_ADDR_INVALID, false);
 }
 
+/**
+ * cec_get_edid_spa_location() - find location of the Source Physical Address
+ *
+ * @edid: the EDID
+ * @size: the size of the EDID
+ *
+ * This EDID is expected to be a CEA-861 compliant, which means that there are
+ * at least two blocks and one or more of the extensions blocks are CEA-861
+ * blocks.
+ *
+ * The returned location is guaranteed to be <= size-2.
+ *
+ * This is an inline function since it is used by both CEC and V4L2.
+ * Ideally this would go in a module shared by both, but it is overkill to do
+ * that for just a single function.
+ */
+static inline unsigned int cec_get_edid_spa_location(const u8 *edid,
+						     unsigned int size)
+{
+	unsigned int blocks = size / 128;
+	unsigned int block;
+	u8 d;
+
+	/* Sanity check: at least 2 blocks and a multiple of the block size */
+	if (blocks < 2 || size % 128)
+		return 0;
+
+	/*
+	 * If there are fewer extension blocks than the size, then update
+	 * 'blocks'. It is allowed to have more extension blocks than the size,
+	 * since some hardware can only read e.g. 256 bytes of the EDID, even
+	 * though more blocks are present. The first CEA-861 extension block
+	 * should normally be in block 1 anyway.
+	 */
+	if (edid[0x7e] + 1 < blocks)
+		blocks = edid[0x7e] + 1;
+
+	for (block = 1; block < blocks; block++) {
+		unsigned int offset = block * 128;
+
+		/* Skip any non-CEA-861 extension blocks */
+		if (edid[offset] != 0x02 || edid[offset + 1] != 0x03)
+			continue;
+
+		/* search Vendor Specific Data Block (tag 3) */
+		d = edid[offset + 2] & 0x7f;
+		/* Check if there are Data Blocks */
+		if (d <= 4)
+			continue;
+		if (d > 4) {
+			unsigned int i = offset + 4;
+			unsigned int end = offset + d;
+
+			/* Note: 'end' is always < 'size' */
+			do {
+				u8 tag = edid[i] >> 5;
+				u8 len = edid[i] & 0x1f;
+
+				if (tag == 3 && len >= 5 && i + len <= end &&
+				    edid[i + 1] == 0x03 &&
+				    edid[i + 2] == 0x0c &&
+				    edid[i + 3] == 0x00)
+					return i + 4;
+				i += len + 1;
+			} while (i < end);
+		}
+	}
+	return 0;
+}
+
 #endif /* _MEDIA_CEC_H */