drm/amd/display: allow query ddc data over aux to be read only operation

[why]
Two issues:
1. Add read only operation support for query ddc data over aux.
2. Fix a bug where if read size is multiple of 16,
mot of the last read transaction will not be set to 0.
Signed-off-by: Wenjing Liu <wenjing.liu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc_link_ddc.c

@@ -503,7 +503,7 @@ bool dal_ddc_service_query_ddc_data(
 	uint8_t *read_buf,
 	uint32_t read_size)
 {
-	bool ret = false;
+	bool success = true;
 	uint32_t payload_size =
 		dal_ddc_service_is_in_aux_transaction_mode(ddc) ?
 			DEFAULT_AUX_MAX_DATA_SIZE : EDID_SEGMENT_SIZE;
@@ -527,7 +527,6 @@ bool dal_ddc_service_query_ddc_data(
 	 *  but we want to read 256 over i2c!!!!*/
 	if (dal_ddc_service_is_in_aux_transaction_mode(ddc)) {
 		struct aux_payload payload;
-		bool read_available = true;
 
 		payload.i2c_over_aux = true;
 		payload.address = address;
@@ -536,21 +535,26 @@ bool dal_ddc_service_query_ddc_data(
 
 		if (write_size != 0) {
 			payload.write = true;
-			payload.mot = false;
+			/* should not set mot (middle of transaction) to 0
+			 * if there are pending read payloads
+			 */
+			payload.mot = read_size == 0 ? false : true;
 			payload.length = write_size;
 			payload.data = write_buf;
 
-			ret = dal_ddc_submit_aux_command(ddc, &payload);
-			read_available = ret;
+			success = dal_ddc_submit_aux_command(ddc, &payload);
 		}
 
-		if (read_size != 0 && read_available) {
+		if (read_size != 0 && success) {
 			payload.write = false;
+			/* should set mot (middle of transaction) to 0
+			 * since it is the last payload to send
+			 */
 			payload.mot = false;
 			payload.length = read_size;
 			payload.data = read_buf;
 
-			ret = dal_ddc_submit_aux_command(ddc, &payload);
+			success = dal_ddc_submit_aux_command(ddc, &payload);
 		}
 	} else {
 		struct i2c_command command = {0};
@@ -573,7 +577,7 @@ bool dal_ddc_service_query_ddc_data(
 		command.number_of_payloads =
 			dal_ddc_i2c_payloads_get_count(&payloads);
 
-		ret = dm_helpers_submit_i2c(
+		success = dm_helpers_submit_i2c(
 				ddc->ctx,
 				ddc->link,
 				&command);
@@ -581,7 +585,7 @@ bool dal_ddc_service_query_ddc_data(
 		dal_ddc_i2c_payloads_destroy(&payloads);
 	}
 
-	return ret;
+	return success;
 }
 
 bool dal_ddc_submit_aux_command(struct ddc_service *ddc,
@@ -598,7 +602,7 @@ bool dal_ddc_submit_aux_command(struct ddc_service *ddc,
 
 	do {
 		struct aux_payload current_payload;
-		bool is_end_of_payload = (retrieved + DEFAULT_AUX_MAX_DATA_SIZE) >
+		bool is_end_of_payload = (retrieved + DEFAULT_AUX_MAX_DATA_SIZE) >=
 			payload->length;
 
 		current_payload.address = payload->address;
@@ -607,7 +611,10 @@ bool dal_ddc_submit_aux_command(struct ddc_service *ddc,
 		current_payload.i2c_over_aux = payload->i2c_over_aux;
 		current_payload.length = is_end_of_payload ?
 			payload->length - retrieved : DEFAULT_AUX_MAX_DATA_SIZE;
-		current_payload.mot = !is_end_of_payload;
+		/* set mot (middle of transaction) to false
+		 * if it is the last payload
+		 */
+		current_payload.mot = is_end_of_payload ? payload->mot:true;
 		current_payload.reply = payload->reply;
 		current_payload.write = payload->write;