xref: /rk3399_rockchip-uboot/drivers/video/drm/drm_mipi_dsi.c (revision a92bdacccc2618a4682820c07546173ffa74b21c)

// SPDX-License-Identifier: GPL-2.0+
/*
 * MIPI DSI Bus
 *
 * Copyright (C) 2012-2013, Samsung Electronics, Co., Ltd.
 * Andrzej Hajda <a.hajda@samsung.com>
 */

#include <drm/drm_mipi_dsi.h>

#include <config.h>
#include <common.h>
#include <errno.h>
#include <malloc.h>

/**
 * mipi_dsi_attach - attach a DSI device to its DSI host
 * @dsi: DSI peripheral
 */
int mipi_dsi_attach(struct mipi_dsi_device *dsi)
{
	const struct mipi_dsi_host_ops *ops = dsi->host->ops;

	if (!ops || !ops->attach)
		return -ENOSYS;

	return ops->attach(dsi->host, dsi);
}

/**
 * mipi_dsi_detach - detach a DSI device from its DSI host
 * @dsi: DSI peripheral
 */
int mipi_dsi_detach(struct mipi_dsi_device *dsi)
{
	const struct mipi_dsi_host_ops *ops = dsi->host->ops;

	if (!ops || !ops->detach)
		return -ENOSYS;

	return ops->detach(dsi->host, dsi);
}

static ssize_t mipi_dsi_device_transfer(struct mipi_dsi_device *dsi,
					struct mipi_dsi_msg *msg)
{
	const struct mipi_dsi_host_ops *ops = dsi->host->ops;

	if (!ops || !ops->transfer)
		return -ENOSYS;

	if (dsi->mode_flags & MIPI_DSI_MODE_LPM)
		msg->flags |= MIPI_DSI_MSG_USE_LPM;

	return ops->transfer(dsi->host, msg);
}

/**
 * mipi_dsi_packet_format_is_short - check if a packet is of the short format
 * @type: MIPI DSI data type of the packet
 *
 * Return: true if the packet for the given data type is a short packet, false
 * otherwise.
 */
bool mipi_dsi_packet_format_is_short(u8 type)
{
	switch (type) {
	case MIPI_DSI_V_SYNC_START:
	case MIPI_DSI_V_SYNC_END:
	case MIPI_DSI_H_SYNC_START:
	case MIPI_DSI_H_SYNC_END:
	case MIPI_DSI_COMPRESSION_MODE:
	case MIPI_DSI_END_OF_TRANSMISSION:
	case MIPI_DSI_COLOR_MODE_OFF:
	case MIPI_DSI_COLOR_MODE_ON:
	case MIPI_DSI_SHUTDOWN_PERIPHERAL:
	case MIPI_DSI_TURN_ON_PERIPHERAL:
	case MIPI_DSI_GENERIC_SHORT_WRITE_0_PARAM:
	case MIPI_DSI_GENERIC_SHORT_WRITE_1_PARAM:
	case MIPI_DSI_GENERIC_SHORT_WRITE_2_PARAM:
	case MIPI_DSI_GENERIC_READ_REQUEST_0_PARAM:
	case MIPI_DSI_GENERIC_READ_REQUEST_1_PARAM:
	case MIPI_DSI_GENERIC_READ_REQUEST_2_PARAM:
	case MIPI_DSI_DCS_SHORT_WRITE:
	case MIPI_DSI_DCS_SHORT_WRITE_PARAM:
	case MIPI_DSI_DCS_READ:
	case MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE:
		return true;
	}

	return false;
}

/**
 * mipi_dsi_packet_format_is_long - check if a packet is of the long format
 * @type: MIPI DSI data type of the packet
 *
 * Return: true if the packet for the given data type is a long packet, false
 * otherwise.
 */
bool mipi_dsi_packet_format_is_long(u8 type)
{
	switch (type) {
	case MIPI_DSI_NULL_PACKET:
	case MIPI_DSI_BLANKING_PACKET:
	case MIPI_DSI_GENERIC_LONG_WRITE:
	case MIPI_DSI_DCS_LONG_WRITE:
	case MIPI_DSI_PICTURE_PARAMETER_SET:
	case MIPI_DSI_COMPRESSED_PIXEL_STREAM:
	case MIPI_DSI_LOOSELY_PACKED_PIXEL_STREAM_YCBCR20:
	case MIPI_DSI_PACKED_PIXEL_STREAM_YCBCR24:
	case MIPI_DSI_PACKED_PIXEL_STREAM_YCBCR16:
	case MIPI_DSI_PACKED_PIXEL_STREAM_30:
	case MIPI_DSI_PACKED_PIXEL_STREAM_36:
	case MIPI_DSI_PACKED_PIXEL_STREAM_YCBCR12:
	case MIPI_DSI_PACKED_PIXEL_STREAM_16:
	case MIPI_DSI_PACKED_PIXEL_STREAM_18:
	case MIPI_DSI_PIXEL_STREAM_3BYTE_18:
	case MIPI_DSI_PACKED_PIXEL_STREAM_24:
		return true;
	}

	return false;
}

/**
 * mipi_dsi_create_packet - create a packet from a message according to the
 *	DSI protocol
 * @packet: pointer to a DSI packet structure
 * @msg: message to translate into a packet
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_create_packet(struct mipi_dsi_packet *packet,
			   const struct mipi_dsi_msg *msg)
{
	if (!packet || !msg)
		return -EINVAL;

	/* do some minimum sanity checking */
	if (!mipi_dsi_packet_format_is_short(msg->type) &&
	    !mipi_dsi_packet_format_is_long(msg->type))
		return -EINVAL;

	if (msg->channel > 3)
		return -EINVAL;

	memset(packet, 0, sizeof(*packet));
	packet->header[0] = ((msg->channel & 0x3) << 6) | (msg->type & 0x3f);
	if (mipi_dsi_packet_format_is_long(msg->type)) {
		packet->header[1] = (msg->tx_len >> 0) & 0xff;
		packet->header[2] = (msg->tx_len >> 8) & 0xff;

		packet->payload_length = msg->tx_len;
		packet->payload = msg->tx_buf;
	} else {
		const u8 *tx = msg->tx_buf;

		packet->header[1] = (msg->tx_len > 0) ? tx[0] : 0;
		packet->header[2] = (msg->tx_len > 1) ? tx[1] : 0;
	}

	packet->size = sizeof(packet->header) + packet->payload_length;

	return 0;
}

/**
 * mipi_dsi_shutdown_peripheral() - sends a Shutdown Peripheral command
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_shutdown_peripheral(struct mipi_dsi_device *dsi)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.type = MIPI_DSI_SHUTDOWN_PERIPHERAL,
		.tx_buf = (u8 [2]) { 0, 0 },
		.tx_len = 2,
	};
	int ret = mipi_dsi_device_transfer(dsi, &msg);

	return (ret < 0) ? ret : 0;
}

/**
 * mipi_dsi_turn_on_peripheral() - sends a Turn On Peripheral command
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_turn_on_peripheral(struct mipi_dsi_device *dsi)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.type = MIPI_DSI_TURN_ON_PERIPHERAL,
		.tx_buf = (u8 [2]) { 0, 0 },
		.tx_len = 2,
	};
	int ret = mipi_dsi_device_transfer(dsi, &msg);

	return (ret < 0) ? ret : 0;
}

/*
 * mipi_dsi_set_maximum_return_packet_size() - specify the maximum size of the
 *	the payload in a long packet transmitted from the peripheral back to the
 *	host processor
 * @dsi: DSI peripheral device
 * @value: the maximum size of the payload
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_set_maximum_return_packet_size(struct mipi_dsi_device *dsi,
					    u16 value)
{
	u8 tx[2] = { value & 0xff, value >> 8 };
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.type = MIPI_DSI_SET_MAXIMUM_RETURN_PACKET_SIZE,
		.tx_len = sizeof(tx),
		.tx_buf = tx,
	};
	int ret = mipi_dsi_device_transfer(dsi, &msg);

	return (ret < 0) ? ret : 0;
}

/**
 * mipi_dsi_compression_mode() - enable/disable DSC on the peripheral
 * @dsi: DSI peripheral device
 * @enable: Whether to enable or disable the DSC
 *
 * Enable or disable Display Stream Compression on the peripheral using the
 * default Picture Parameter Set and VESA DSC 1.1 algorithm.
 *
 * Return: 0 on success or a negative error code on failure.
 */
ssize_t mipi_dsi_compression_mode(struct mipi_dsi_device *dsi, bool enable)
{
	/* Note: Needs updating for non-default PPS or algorithm */
	u8 tx[2] = { enable << 0, 0 };
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.type = MIPI_DSI_COMPRESSION_MODE,
		.tx_len = sizeof(tx),
		.tx_buf = tx,
	};
	int ret = mipi_dsi_device_transfer(dsi, &msg);

	return (ret < 0) ? ret : 0;
}

/**
 * mipi_dsi_picture_parameter_set() - transmit the DSC PPS to the peripheral
 * @dsi: DSI peripheral device
 * @pps: VESA DSC 1.1 Picture Parameter Set
 *
 * Transmit the VESA DSC 1.1 Picture Parameter Set to the peripheral.
 *
 * Return: 0 on success or a negative error code on failure.
 */
ssize_t mipi_dsi_picture_parameter_set(struct mipi_dsi_device *dsi,
				       const struct drm_dsc_picture_parameter_set *pps)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.type = MIPI_DSI_PICTURE_PARAMETER_SET,
		.tx_len = sizeof(*pps),
		.tx_buf = pps,
	};
	int ret = mipi_dsi_device_transfer(dsi, &msg);

	return (ret < 0) ? ret : 0;
}

/**
 * mipi_dsi_generic_write() - transmit data using a generic write packet
 * @dsi: DSI peripheral device
 * @payload: buffer containing the payload
 * @size: size of payload buffer
 *
 * This function will automatically choose the right data type depending on
 * the payload length.
 *
 * Return: The number of bytes transmitted on success or a negative error code
 * on failure.
 */
ssize_t mipi_dsi_generic_write(struct mipi_dsi_device *dsi, const void *payload,
			       size_t size)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.tx_buf = payload,
		.tx_len = size
	};

	switch (size) {
	case 0:
		msg.type = MIPI_DSI_GENERIC_SHORT_WRITE_0_PARAM;
		break;
	case 1:
		msg.type = MIPI_DSI_GENERIC_SHORT_WRITE_1_PARAM;
		break;
	case 2:
		msg.type = MIPI_DSI_GENERIC_SHORT_WRITE_2_PARAM;
		break;
	default:
		msg.type = MIPI_DSI_GENERIC_LONG_WRITE;
		break;
	}

	return mipi_dsi_device_transfer(dsi, &msg);
}

/**
 * mipi_dsi_generic_read() - receive data using a generic read packet
 * @dsi: DSI peripheral device
 * @params: buffer containing the request parameters
 * @num_params: number of request parameters
 * @data: buffer in which to return the received data
 * @size: size of receive buffer
 *
 * This function will automatically choose the right data type depending on
 * the number of parameters passed in.
 *
 * Return: The number of bytes successfully read or a negative error code on
 * failure.
 */
ssize_t mipi_dsi_generic_read(struct mipi_dsi_device *dsi, const void *params,
			      size_t num_params, void *data, size_t size)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.tx_len = num_params,
		.tx_buf = params,
		.rx_len = size,
		.rx_buf = data
	};

	switch (num_params) {
	case 0:
		msg.type = MIPI_DSI_GENERIC_READ_REQUEST_0_PARAM;
		break;

	case 1:
		msg.type = MIPI_DSI_GENERIC_READ_REQUEST_1_PARAM;
		break;

	case 2:
		msg.type = MIPI_DSI_GENERIC_READ_REQUEST_2_PARAM;
		break;

	default:
		return -EINVAL;
	}

	return mipi_dsi_device_transfer(dsi, &msg);
}

/**
 * mipi_dsi_dcs_write_buffer() - transmit a DCS command with payload
 * @dsi: DSI peripheral device
 * @data: buffer containing data to be transmitted
 * @len: size of transmission buffer
 *
 * This function will automatically choose the right data type depending on
 * the command payload length.
 *
 * Return: The number of bytes successfully transmitted or a negative error
 * code on failure.
 */
ssize_t mipi_dsi_dcs_write_buffer(struct mipi_dsi_device *dsi,
				  const void *data, size_t len)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.tx_buf = data,
		.tx_len = len
	};

	switch (len) {
	case 0:
		return -EINVAL;

	case 1:
		msg.type = MIPI_DSI_DCS_SHORT_WRITE;
		break;

	case 2:
		msg.type = MIPI_DSI_DCS_SHORT_WRITE_PARAM;
		break;

	default:
		msg.type = MIPI_DSI_DCS_LONG_WRITE;
		break;
	}

	return mipi_dsi_device_transfer(dsi, &msg);
}

/**
 * mipi_dsi_dcs_write() - send DCS write command
 * @dsi: DSI peripheral device
 * @cmd: DCS command
 * @data: buffer containing the command payload
 * @len: command payload length
 *
 * This function will automatically choose the right data type depending on
 * the command payload length.
 *
 * Return: The number of bytes successfully transmitted or a negative error
 * code on failure.
 */
ssize_t mipi_dsi_dcs_write(struct mipi_dsi_device *dsi, u8 cmd,
			   const void *data, size_t len)
{
	ssize_t err;
	size_t size;
	u8 *tx;

	if (len > 0) {
		size = 1 + len;

		tx = malloc(size);
		if (!tx)
			return -ENOMEM;

		/* concatenate the DCS command byte and the payload */
		tx[0] = cmd;
		memcpy(&tx[1], data, len);
	} else {
		tx = &cmd;
		size = 1;
	}

	err = mipi_dsi_dcs_write_buffer(dsi, tx, size);

	if (len > 0)
		free(tx);

	return err;
}

/**
 * mipi_dsi_dcs_read() - send DCS read request command
 * @dsi: DSI peripheral device
 * @cmd: DCS command
 * @data: buffer in which to receive data
 * @len: size of receive buffer
 * Return: The number of bytes read or a negative error code on failure.
 */
ssize_t mipi_dsi_dcs_read(struct mipi_dsi_device *dsi, u8 cmd, void *data,
			  size_t len)
{
	struct mipi_dsi_msg msg = {
		.channel = dsi->channel,
		.type = MIPI_DSI_DCS_READ,
		.tx_buf = &cmd,
		.tx_len = 1,
		.rx_buf = data,
		.rx_len = len
	};

	return mipi_dsi_device_transfer(dsi, &msg);
}

/**
 * mipi_dsi_dcs_nop() - send DCS nop packet
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_nop(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_NOP, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_soft_reset() - perform a software reset of the display module
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_soft_reset(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SOFT_RESET, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_get_power_mode() - query the display module's current power
 *	mode
 * @dsi: DSI peripheral device
 * @mode: return location for the current power mode
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_get_power_mode(struct mipi_dsi_device *dsi, u8 *mode)
{
	ssize_t err;

	err = mipi_dsi_dcs_read(dsi, MIPI_DCS_GET_POWER_MODE, mode,
				sizeof(*mode));
	if (err <= 0) {
		if (err == 0)
			err = -ENODATA;

		return err;
	}

	return 0;
}

/**
 * mipi_dsi_dcs_get_pixel_format() - gets the pixel format for the RGB image
 *	data used by the interface
 * @dsi: DSI peripheral device
 * @format: return location for the pixel format
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_get_pixel_format(struct mipi_dsi_device *dsi, u8 *format)
{
	ssize_t err;

	err = mipi_dsi_dcs_read(dsi, MIPI_DCS_GET_PIXEL_FORMAT, format,
				sizeof(*format));
	if (err <= 0) {
		if (err == 0)
			err = -ENODATA;

		return err;
	}

	return 0;
}

/**
 * mipi_dsi_dcs_enter_sleep_mode() - disable all unnecessary blocks inside the
 *	display module except interface communication
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_enter_sleep_mode(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_ENTER_SLEEP_MODE, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_exit_sleep_mode() - enable all blocks inside the display
 *	module
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_exit_sleep_mode(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_EXIT_SLEEP_MODE, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_display_off() - stop displaying the image data on the
 *	display device
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_set_display_off(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_DISPLAY_OFF, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_display_on() - start displaying the image data on the
 *	display device
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure
 */
int mipi_dsi_dcs_set_display_on(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_DISPLAY_ON, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_column_address() - define the column extent of the frame
 *	memory accessed by the host processor
 * @dsi: DSI peripheral device
 * @start: first column of frame memory
 * @end: last column of frame memory
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_set_column_address(struct mipi_dsi_device *dsi, u16 start,
				    u16 end)
{
	u8 payload[4] = { start >> 8, start & 0xff, end >> 8, end & 0xff };
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_COLUMN_ADDRESS, payload,
				 sizeof(payload));
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_page_address() - define the page extent of the frame
 *	memory accessed by the host processor
 * @dsi: DSI peripheral device
 * @start: first page of frame memory
 * @end: last page of frame memory
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_set_page_address(struct mipi_dsi_device *dsi, u16 start,
				  u16 end)
{
	u8 payload[4] = { start >> 8, start & 0xff, end >> 8, end & 0xff };
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_PAGE_ADDRESS, payload,
				 sizeof(payload));
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_tear_off() - turn off the display module's Tearing Effect
 *	output signal on the TE signal line
 * @dsi: DSI peripheral device
 *
 * Return: 0 on success or a negative error code on failure
 */
int mipi_dsi_dcs_set_tear_off(struct mipi_dsi_device *dsi)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_TEAR_OFF, NULL, 0);
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_tear_on() - turn on the display module's Tearing Effect
 *	output signal on the TE signal line.
 * @dsi: DSI peripheral device
 * @mode: the Tearing Effect Output Line mode
 *
 * Return: 0 on success or a negative error code on failure
 */
int mipi_dsi_dcs_set_tear_on(struct mipi_dsi_device *dsi,
			     enum mipi_dsi_dcs_tear_mode mode)
{
	u8 value = mode;
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_TEAR_ON, &value,
				 sizeof(value));
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_pixel_format() - sets the pixel format for the RGB image
 *	data used by the interface
 * @dsi: DSI peripheral device
 * @format: pixel format
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_set_pixel_format(struct mipi_dsi_device *dsi, u8 format)
{
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_PIXEL_FORMAT, &format,
				 sizeof(format));
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_tear_scanline() - set the scanline to use as trigger for
 *	the Tearing Effect output signal of the display module
 * @dsi: DSI peripheral device
 * @scanline: scanline to use as trigger
 *
 * Return: 0 on success or a negative error code on failure
 */
int mipi_dsi_dcs_set_tear_scanline(struct mipi_dsi_device *dsi, u16 scanline)
{
	u8 payload[3] = { MIPI_DCS_SET_TEAR_SCANLINE, scanline >> 8,
				scanline & 0xff };
	ssize_t err;

	err = mipi_dsi_generic_write(dsi, payload, sizeof(payload));
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_set_display_brightness() - sets the brightness value of the
 *	display
 * @dsi: DSI peripheral device
 * @brightness: brightness value
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_set_display_brightness(struct mipi_dsi_device *dsi,
					u16 brightness)
{
	u8 payload[2] = { brightness & 0xff, brightness >> 8 };
	ssize_t err;

	err = mipi_dsi_dcs_write(dsi, MIPI_DCS_SET_DISPLAY_BRIGHTNESS,
				 payload, sizeof(payload));
	if (err < 0)
		return err;

	return 0;
}

/**
 * mipi_dsi_dcs_get_display_brightness() - gets the current brightness value
 *	of the display
 * @dsi: DSI peripheral device
 * @brightness: brightness value
 *
 * Return: 0 on success or a negative error code on failure.
 */
int mipi_dsi_dcs_get_display_brightness(struct mipi_dsi_device *dsi,
					u16 *brightness)
{
	ssize_t err;

	err = mipi_dsi_dcs_read(dsi, MIPI_DCS_GET_DISPLAY_BRIGHTNESS,
				brightness, sizeof(*brightness));
	if (err <= 0) {
		if (err == 0)
			err = -ENODATA;

		return err;
	}

	return 0;
}