cta: add support for VESA Display Transfer Characteristic data block

Signed-off-by: Sebastian Wick <sebastian.wick@redhat.com>

cta.c

@@ -214,6 +214,29 @@ parse_hdr_static_metadata_block(struct di_edid_cta *cta,
 	return true;
 }
 
+static bool
+parse_vesa_transfer_characteristics_block(struct di_edid_cta *cta,
+					  struct di_cta_vesa_transfer_characteristics *tf,
+					  const uint8_t *data, size_t size)
+{
+	size_t i;
+
+	if (size != 7 && size != 15 && size != 31) {
+		add_failure(cta, "Invalid length %u.", size);
+		return false;
+	}
+
+	tf->points_len = (uint8_t) size + 1;
+	tf->usage = get_bit_range(data[0], 7, 6);
+
+	tf->points[0] = get_bit_range(data[0], 5, 0) / 1023.0f;
+	for (i = 1; i < size; i++)
+		tf->points[i] = tf->points[i - 1] + data[i] / 1023.0f;
+	tf->points[i] = 1.0f;
+
+	return true;
+}
+
 static void
 destroy_data_block(struct di_cta_data_block *data_block)
 {
@@ -262,6 +285,10 @@ parse_data_block(struct di_edid_cta *cta, uint8_t raw_tag, const uint8_t *data,
 		break;
 	case 5:
 		tag = DI_CTA_DATA_BLOCK_VESA_DISPLAY_TRANSFER_CHARACTERISTIC;
+		if (!parse_vesa_transfer_characteristics_block(cta,
+							       &data_block->vesa_transfer_characteristics,
+							       data, size))
+			goto error;
 		break;
 	case 7:
 		/* Use Extended Tag */
@@ -536,3 +563,12 @@ di_edid_cta_get_detailed_timing_defs(const struct di_edid_cta *cta)
 {
 	return (const struct di_edid_detailed_timing_def *const *) cta->detailed_timing_defs;
 }
+
+const struct di_cta_vesa_transfer_characteristics *
+di_cta_data_block_get_vesa_transfer_characteristics(const struct di_cta_data_block *block)
+{
+	if (block->tag != DI_CTA_DATA_BLOCK_VESA_DISPLAY_TRANSFER_CHARACTERISTIC) {
+		return NULL;
+	}
+	return &block->vesa_transfer_characteristics;
+}

di-edid-decode.c

@@ -14,6 +14,7 @@
 static struct {
 	bool color_point_descriptor;
 	bool color_management_data;
+	bool cta_transfer_characteristics;
 } contains_uncommon_feature;
 
 static size_t num_detailed_timing_defs = 0;
@@ -703,6 +704,34 @@ print_cta_hdr_static_metadata(const struct di_cta_hdr_static_metadata_block *met
 		       metadata->desired_content_min_luminance);
 }
 
+static void
+print_cta_vesa_transfer_characteristics(const struct di_cta_vesa_transfer_characteristics *tf)
+{
+	size_t i;
+
+	switch (tf->usage) {
+	case DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_WHITE:
+		printf("    White");
+		break;
+	case DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_RED:
+		printf("    Red");
+		break;
+	case DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_GREEN:
+		printf("    Green");
+		break;
+	case DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_BLUE:
+		printf("    Blue");
+		break;
+	}
+
+	printf(" transfer characteristics:");
+	for (i = 0; i < tf->points_len; i++)
+		printf(" %u", (uint16_t) (tf->points[i] * 1023.0f));
+	printf("\n");
+
+	contains_uncommon_feature.cta_transfer_characteristics = true;
+}
+
 static const char *
 cta_data_block_tag_name(enum di_cta_data_block_tag tag)
 {
@@ -781,6 +810,7 @@ print_cta(const struct di_edid_cta *cta)
 	const struct di_cta_video_cap_block *video_cap;
 	const struct di_cta_colorimetry_block *colorimetry;
 	const struct di_cta_hdr_static_metadata_block *hdr_static_metadata;
+	const struct di_cta_vesa_transfer_characteristics *transfer_characteristics;
 	size_t i;
 	const struct di_edid_detailed_timing_def *const *detailed_timing_defs;
 
@@ -858,6 +888,10 @@ print_cta(const struct di_edid_cta *cta)
 			hdr_static_metadata = di_cta_data_block_get_hdr_static_metadata(data_block);
 			print_cta_hdr_static_metadata(hdr_static_metadata);
 			break;
+		case DI_CTA_DATA_BLOCK_VESA_DISPLAY_TRANSFER_CHARACTERISTIC:
+			transfer_characteristics = di_cta_data_block_get_vesa_transfer_characteristics(data_block);
+			print_cta_vesa_transfer_characteristics(transfer_characteristics);
+			break;
 		default:
 			break; /* Ignore */
 		}
@@ -1312,6 +1346,11 @@ main(int argc, char *argv[])
 				"Management Data Descriptor. Please share the "
 				"EDID blob with upstream!\n");
 	}
+	if (contains_uncommon_feature.cta_transfer_characteristics) {
+		fprintf(stderr, "The EDID blob contains an uncommon CTA VESA "
+				"Display Transfer Characteristic data block. "
+				"Please share the EDID blob with upstream!\n");
+	}
 
 	di_info_destroy(info);
 	return failure_msg ? 254 : 0;

include/cta.h

@@ -72,6 +72,8 @@ struct di_cta_data_block {
 	struct di_cta_colorimetry_block colorimetry;
 	/* Used for DI_CTA_DATA_BLOCK_HDR_STATIC_METADATA */
 	struct di_cta_hdr_static_metadata_block_priv hdr_static_metadata;
+	/* Used for DI_CTA_DATA_BLOCK_VESA_DISPLAY_TRANSFER_CHARACTERISTIC */
+	struct di_cta_vesa_transfer_characteristics vesa_transfer_characteristics;
 };
 
 bool

include/libdisplay-info/cta.h

@@ -259,6 +259,44 @@ struct di_cta_svd {
 const struct di_cta_svd *const *
 di_cta_data_block_get_svds(const struct di_cta_data_block *block);
 
+enum di_cta_vesa_transfer_characteristics_usage {
+	/* White transfer characteristic */
+	DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_WHITE = 0,
+	/* Red transfer characteristic */
+	DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_RED = 1,
+	/* Green transfer characteristic */
+	DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_GREEN = 2,
+	/* Blue transfer characteristic */
+	DI_CTA_VESA_TRANSFER_CHARACTERISTIC_USAGE_BLUE = 3,
+};
+
+/**
+ * VESA Display Transfer Characteristic Data Block, defined in VESA Display
+ * Transfer Characteristics Data Block Standard Version 1.0
+ *
+ * Contains 8, 16 or 32 evenly distributed points on the input axis describing
+ * the normalized relative luminance at that input. The first value includes the
+ * relative black level luminance.
+ */
+struct di_cta_vesa_transfer_characteristics {
+	enum di_cta_vesa_transfer_characteristics_usage usage;
+	uint8_t points_len;
+	float points[32];
+};
+
+/**
+ * Get the Display Transfer Characteristic from a CTA data block.
+ *
+ * Returns NULL if the data block tag is not
+ * DI_CTA_DATA_BLOCK_VESA_DISPLAY_TRANSFER_CHARACTERISTIC.
+ *
+ * Upstream is not aware of any EDID blob containing a Display Transfer
+ * Characteristic data block.
+ * If such a blob is found, please share it with upstream!
+ */
+const struct di_cta_vesa_transfer_characteristics *
+di_cta_data_block_get_vesa_transfer_characteristics(const struct di_cta_data_block *block);
+
 /**
  * Get a list of EDID detailed timing definitions.
  *