path: root/lib/qmi_encdec.c

/* Copyright (c) 2012-2015, 2019 The Linux Foundation. All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 and
 * only version 2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 */

#include <linux/slab.h>
#include <linux/uaccess.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/errno.h>
#include <linux/io.h>
#include <linux/string.h>
#include <linux/qmi_encdec.h>

#include "qmi_encdec_priv.h"

#define TLV_LEN_SIZE sizeof(uint16_t)
#define TLV_TYPE_SIZE sizeof(uint8_t)
#define OPTIONAL_TLV_TYPE_START 0x10

#ifdef CONFIG_QMI_ENCDEC_DEBUG

#define qmi_encdec_dump(prefix_str, buf, buf_len) do { \
	const u8 *ptr = buf; \
	int i, linelen, remaining = buf_len; \
	int rowsize = 16, groupsize = 1; \
	unsigned char linebuf[256]; \
	for (i = 0; i < buf_len; i += rowsize) { \
		linelen = min(remaining, rowsize); \
		remaining -= linelen; \
		hex_dump_to_buffer(ptr + i, linelen, rowsize, groupsize, \
				   linebuf, sizeof(linebuf), false); \
		pr_debug("%s: %s\n", prefix_str, linebuf); \
	} \
} while (0)

#define QMI_ENCODE_LOG_MSG(buf, buf_len) do { \
	qmi_encdec_dump("QMI_ENCODE_MSG", buf, buf_len); \
} while (0)

#define QMI_DECODE_LOG_MSG(buf, buf_len) do { \
	qmi_encdec_dump("QMI_DECODE_MSG", buf, buf_len); \
} while (0)

#define QMI_ENCODE_LOG_ELEM(level, elem_len, elem_size, buf) do { \
	pr_debug("QMI_ENCODE_ELEM lvl: %d, len: %d, size: %d\n", \
		 level, elem_len, elem_size); \
	qmi_encdec_dump("QMI_ENCODE_ELEM", buf, (elem_len * elem_size)); \
} while (0)

#define QMI_DECODE_LOG_ELEM(level, elem_len, elem_size, buf) do { \
	pr_debug("QMI_DECODE_ELEM lvl: %d, len: %d, size: %d\n", \
		 level, elem_len, elem_size); \
	qmi_encdec_dump("QMI_DECODE_ELEM", buf, (elem_len * elem_size)); \
} while (0)

#define QMI_ENCODE_LOG_TLV(tlv_type, tlv_len) do { \
	pr_debug("QMI_ENCODE_TLV type: %d, len: %d\n", tlv_type, tlv_len); \
} while (0)

#define QMI_DECODE_LOG_TLV(tlv_type, tlv_len) do { \
	pr_debug("QMI_DECODE_TLV type: %d, len: %d\n", tlv_type, tlv_len); \
} while (0)

#else

#define QMI_ENCODE_LOG_MSG(buf, buf_len) { }
#define QMI_DECODE_LOG_MSG(buf, buf_len) { }
#define QMI_ENCODE_LOG_ELEM(level, elem_len, elem_size, buf) { }
#define QMI_DECODE_LOG_ELEM(level, elem_len, elem_size, buf) { }
#define QMI_ENCODE_LOG_TLV(tlv_type, tlv_len) { }
#define QMI_DECODE_LOG_TLV(tlv_type, tlv_len) { }

#endif

static int _qmi_kernel_encode(struct elem_info *ei_array,
			      void *out_buf, void *in_c_struct,
			      uint32_t out_buf_len, int enc_level);

static int _qmi_kernel_decode(struct elem_info *ei_array,
			      void *out_c_struct,
			      void *in_buf, uint32_t in_buf_len,
			      int dec_level);
static struct elem_info *skip_to_next_elem(struct elem_info *ei_array,
					   int level);

/**
 * qmi_calc_max_msg_len() - Calculate the maximum length of a QMI message
 * @ei_array: Struct info array describing the structure.
 * @level: Level to identify the depth of the nested structures.
 *
 * @return: expected maximum length of the QMI message or 0 on failure.
 */
static int qmi_calc_max_msg_len(struct elem_info *ei_array,
				int level)
{
	int max_msg_len = 0;
	struct elem_info *temp_ei;

	if (!ei_array)
		return max_msg_len;

	for (temp_ei = ei_array; temp_ei->data_type != QMI_EOTI; temp_ei++) {
		/* Flag to identify the optional element is not encoded */
		if (temp_ei->data_type == QMI_OPT_FLAG)
			continue;

		if (temp_ei->data_type == QMI_DATA_LEN) {
			max_msg_len += (temp_ei->elem_size == sizeof(uint8_t) ?
					sizeof(uint8_t) : sizeof(uint16_t));
			continue;
		} else if (temp_ei->data_type == QMI_STRUCT) {
			max_msg_len += (temp_ei->elem_len *
					qmi_calc_max_msg_len(temp_ei->ei_array,
							    (level + 1)));
		} else if (temp_ei->data_type == QMI_STRING) {
			if (level > 1)
				max_msg_len += temp_ei->elem_len <= U8_MAX ?
					sizeof(uint8_t) : sizeof(uint16_t);
			max_msg_len += temp_ei->elem_len * temp_ei->elem_size;
		} else {
			max_msg_len += (temp_ei->elem_len * temp_ei->elem_size);
		}

		/*
		 * Type & Length info. not prepended for elements in the
		 * nested structure.
		 */
		if (level == 1)
			max_msg_len += (TLV_TYPE_SIZE + TLV_LEN_SIZE);
	}
	return max_msg_len;
}

/**
 * qmi_calc_min_msg_len() - Calculate the minimum length of a QMI message
 * @ei_array: Struct info array describing the structure.
 * @level: Level to identify the depth of the nested structures.
 *
 * @return: expected minimum length of the QMI message or 0 on failure.
 */
static int qmi_calc_min_msg_len(struct elem_info *ei_array,
				int level)
{
	int min_msg_len = 0;
	struct elem_info *temp_ei = ei_array;

	if (!ei_array)
		return min_msg_len;

	while (temp_ei->data_type != QMI_EOTI) {
		/* Optional elements do not count in minimum length */
		if (temp_ei->data_type == QMI_OPT_FLAG) {
			temp_ei = skip_to_next_elem(temp_ei, level);
			continue;
		}

		if (temp_ei->data_type == QMI_DATA_LEN) {
			min_msg_len += (temp_ei->elem_size == sizeof(uint8_t) ?
					sizeof(uint8_t) : sizeof(uint16_t));
			temp_ei++;
			continue;
		} else if (temp_ei->data_type == QMI_STRUCT) {
			min_msg_len += qmi_calc_min_msg_len(temp_ei->ei_array,
							    (level + 1));
			temp_ei++;
		} else if (temp_ei->data_type == QMI_STRING) {
			if (level > 1)
				min_msg_len += temp_ei->elem_len <= U8_MAX ?
					sizeof(uint8_t) : sizeof(uint16_t);
			min_msg_len += temp_ei->elem_len * temp_ei->elem_size;
			temp_ei++;
		} else {
			min_msg_len += (temp_ei->elem_len * temp_ei->elem_size);
			temp_ei++;
		}

		/*
		 * Type & Length info. not prepended for elements in the
		 * nested structure.
		 */
		if (level == 1)
			min_msg_len += (TLV_TYPE_SIZE + TLV_LEN_SIZE);
	}
	return min_msg_len;
}

/**
 * qmi_verify_max_msg_len() - Verify the maximum length of a QMI message
 * @desc: Pointer to structure descriptor.
 *
 * @return: true if the maximum message length embedded in structure
 *          descriptor matches the calculated value, else false.
 */
bool qmi_verify_max_msg_len(struct msg_desc *desc)
{
	int calc_max_msg_len;

	if (!desc)
		return false;

	calc_max_msg_len = qmi_calc_max_msg_len(desc->ei_array, 1);
	if (calc_max_msg_len != desc->max_msg_len) {
		pr_err("%s: Calc. len %d != Passed len %d\n",
			__func__, calc_max_msg_len, desc->max_msg_len);
		return false;
	}
	return true;
}

/**
 * qmi_kernel_encode() - Encode to QMI message wire format
 * @desc: Pointer to structure descriptor.
 * @out_buf: Buffer to hold the encoded QMI message.
 * @out_buf_len: Length of the out buffer.
 * @in_c_struct: C Structure to be encoded.
 *
 * @return: size of encoded message on success, < 0 for error.
 */
int qmi_kernel_encode(struct msg_desc *desc,
		      void *out_buf, uint32_t out_buf_len,
		      void *in_c_struct)
{
	int enc_level = 1;
	int ret, calc_max_msg_len, calc_min_msg_len;

	if (!desc)
		return -EINVAL;

	/* Check the possibility of a zero length QMI message */
	if (!in_c_struct) {
		calc_min_msg_len = qmi_calc_min_msg_len(desc->ei_array, 1);
		if (calc_min_msg_len) {
			pr_err("%s: Calc. len %d != 0, but NULL in_c_struct\n",
				__func__, calc_min_msg_len);
			return -EINVAL;
		} else {
			return 0;
		}
	}

	/*
	 * Not a zero-length message. Ensure the output buffer and
	 * element information array are not NULL.
	 */
	if (!out_buf || !desc->ei_array)
		return -EINVAL;

	if (desc->max_msg_len < out_buf_len)
		return -ETOOSMALL;

	ret = _qmi_kernel_encode(desc->ei_array, out_buf,
				 in_c_struct, out_buf_len, enc_level);
	if (ret == -ETOOSMALL) {
		calc_max_msg_len = qmi_calc_max_msg_len(desc->ei_array, 1);
		pr_err("%s: Calc. len %d != Out buf len %d\n",
			__func__, calc_max_msg_len, out_buf_len);
	}
	return ret;
}
EXPORT_SYMBOL(qmi_kernel_encode);

/**
 * qmi_encode_basic_elem() - Encodes elements of basic/primary data type
 * @buf_dst: Buffer to store the encoded information.
 * @buf_src: Buffer containing the elements to be encoded.
 * @elem_len: Number of elements, in the buf_src, to be encoded.
 * @elem_size: Size of a single instance of the element to be encoded.
 *
 * @return: number of bytes of encoded information.
 *
 * This function encodes the "elem_len" number of data elements, each of
 * size "elem_size" bytes from the source buffer "buf_src" and stores the
 * encoded information in the destination buffer "buf_dst". The elements are
 * of primary data type which include uint8_t - uint64_t or similar. This
 * function returns the number of bytes of encoded information.
 */
static int qmi_encode_basic_elem(void *buf_dst, void *buf_src,
				 uint32_t elem_len, uint32_t elem_size)
{
	uint32_t i, rc = 0;

	for (i = 0; i < elem_len; i++) {
		QMI_ENCDEC_ENCODE_N_BYTES(buf_dst, buf_src, elem_size);
		rc += elem_size;
	}

	return rc;
}

/**
 * qmi_encode_struct_elem() - Encodes elements of struct data type
 * @ei_array: Struct info array descibing the struct element.
 * @buf_dst: Buffer to store the encoded information.
 * @buf_src: Buffer containing the elements to be encoded.
 * @elem_len: Number of elements, in the buf_src, to be encoded.
 * @out_buf_len: Available space in the encode buffer.
 * @enc_level: Depth of the nested structure from the main structure.
 *
 * @return: Mumber of bytes of encoded information, on success.
 *          < 0 on error.
 *
 * This function encodes the "elem_len" number of struct elements, each of
 * size "ei_array->elem_size" bytes from the source buffer "buf_src" and
 * stores the encoded information in the destination buffer "buf_dst". The
 * elements are of struct data type which includes any C structure. This
 * function returns the number of bytes of encoded information.
 */
static int qmi_encode_struct_elem(struct elem_info *ei_array,
				  void *buf_dst, void *buf_src,
				  uint32_t elem_len, uint32_t out_buf_len,
				  int enc_level)
{
	int i, rc, encoded_bytes = 0;
	struct elem_info *temp_ei = ei_array;

	for (i = 0; i < elem_len; i++) {
		rc = _qmi_kernel_encode(temp_ei->ei_array, buf_dst, buf_src,
					(out_buf_len - encoded_bytes),
					enc_level);
		if (rc < 0) {
			pr_err("%s: STRUCT Encode failure\n", __func__);
			return rc;
		}
		buf_dst = buf_dst + rc;
		buf_src = buf_src + temp_ei->elem_size;
		encoded_bytes += rc;
	}

	return encoded_bytes;
}

/**
 * qmi_encode_string_elem() - Encodes elements of string data type
 * @ei_array: Struct info array descibing the string element.
 * @buf_dst: Buffer to store the encoded information.
 * @buf_src: Buffer containing the elements to be encoded.
 * @out_buf_len: Available space in the encode buffer.
 * @enc_level: Depth of the string element from the main structure.
 *
 * @return: Mumber of bytes of encoded information, on success.
 *          < 0 on error.
 *
 * This function encodes a string element of maximum length "ei_array->elem_len"
 * bytes from the source buffer "buf_src" and stores the encoded information in
 * the destination buffer "buf_dst". This function returns the number of bytes
 * of encoded information.
 */
static int qmi_encode_string_elem(struct elem_info *ei_array,
				  void *buf_dst, void *buf_src,
				  uint32_t out_buf_len, int enc_level)
{
	int rc;
	int encoded_bytes = 0;
	struct elem_info *temp_ei = ei_array;
	uint32_t string_len = 0;
	uint32_t string_len_sz = 0;

	string_len = strlen(buf_src);
	string_len_sz = temp_ei->elem_len <= U8_MAX ?
			sizeof(uint8_t) : sizeof(uint16_t);
	if (string_len > temp_ei->elem_len) {
		pr_err("%s: String to be encoded is longer - %d > %d\n",
			__func__, string_len, temp_ei->elem_len);
		return -EINVAL;
	}

	if (enc_level == 1) {
		if (string_len + TLV_LEN_SIZE + TLV_TYPE_SIZE >
		    out_buf_len) {
			pr_err("%s: Output len %d > Out Buf len %d\n",
				__func__, string_len, out_buf_len);
			return -ETOOSMALL;
		}
	} else {
		if (string_len + string_len_sz > out_buf_len) {
			pr_err("%s: Output len %d > Out Buf len %d\n",
				__func__, string_len, out_buf_len);
			return -ETOOSMALL;
		}
		rc = qmi_encode_basic_elem(buf_dst, &string_len,
					   1, string_len_sz);
		encoded_bytes += rc;
	}

	rc = qmi_encode_basic_elem(buf_dst + encoded_bytes, buf_src,
				   string_len, temp_ei->elem_size);
	encoded_bytes += rc;
	QMI_ENCODE_LOG_ELEM(enc_level, string_len, temp_ei->elem_size, buf_src);
	return encoded_bytes;
}

/**
 * skip_to_next_elem() - Skip to next element in the structure to be encoded
 * @ei_array: Struct info describing the element to be skipped.
 * @level: Depth level of encoding/decoding to identify nested structures.
 *
 * @return: Struct info of the next element that can be encoded.
 *
 * This function is used while encoding optional elements. If the flag
 * corresponding to an optional element is not set, then encoding the
 * optional element can be skipped. This function can be used to perform
 * that operation.
 */
static struct elem_info *skip_to_next_elem(struct elem_info *ei_array,
					   int level)
{
	struct elem_info *temp_ei = ei_array;
	uint8_t tlv_type;

	if (level > 1) {
		temp_ei = temp_ei + 1;
	} else {
		do {
			tlv_type = temp_ei->tlv_type;
			temp_ei = temp_ei + 1;
		} while (tlv_type == temp_ei->tlv_type);
	}

	return temp_ei;
}

/**
 * _qmi_kernel_encode() - Core Encode Function
 * @ei_array: Struct info array describing the structure to be encoded.
 * @out_buf: Buffer to hold the encoded QMI message.
 * @in_c_struct: Pointer to the C structure to be encoded.
 * @out_buf_len: Available space in the encode buffer.
 * @enc_level: Encode level to indicate the depth of the nested structure,
 *             within the main structure, being encoded.
 *
 * @return: Number of bytes of encoded information, on success.
 *          < 0 on error.
 */
static int _qmi_kernel_encode(struct elem_info *ei_array,
			      void *out_buf, void *in_c_struct,
			      uint32_t out_buf_len, int enc_level)
{
	struct elem_info *temp_ei = ei_array;
	uint8_t opt_flag_value = 0;
	uint32_t data_len_value = 0, data_len_sz;
	uint8_t *buf_dst = (uint8_t *)out_buf;
	uint8_t *tlv_pointer;
	uint32_t tlv_len;
	uint8_t tlv_type;
	uint32_t encoded_bytes = 0;
	void *buf_src;
	int encode_tlv = 0;
	int rc;

	tlv_pointer = buf_dst;
	tlv_len = 0;
	if (enc_level == 1)
		buf_dst = buf_dst + (TLV_LEN_SIZE + TLV_TYPE_SIZE);

	while (temp_ei->data_type != QMI_EOTI) {
		buf_src = in_c_struct + temp_ei->offset;
		tlv_type = temp_ei->tlv_type;

		if (temp_ei->is_array == NO_ARRAY) {
			data_len_value = 1;
		} else if (temp_ei->is_array == STATIC_ARRAY) {
			data_len_value = temp_ei->elem_len;
		} else if (data_len_value <= 0 ||
			    temp_ei->elem_len < data_len_value) {
			pr_err("%s: Invalid data length\n", __func__);
			return -EINVAL;
		}

		switch (temp_ei->data_type) {
		case QMI_OPT_FLAG:
			rc = qmi_encode_basic_elem(&opt_flag_value, buf_src,
						   1, sizeof(uint8_t));
			if (opt_flag_value)
				temp_ei = temp_ei + 1;
			else
				temp_ei = skip_to_next_elem(temp_ei, enc_level);
			break;

		case QMI_DATA_LEN:
			memcpy(&data_len_value, buf_src, temp_ei->elem_size);
			data_len_sz = temp_ei->elem_size == sizeof(uint8_t) ?
					sizeof(uint8_t) : sizeof(uint16_t);
			/* Check to avoid out of range buffer access */
			if ((data_len_sz + encoded_bytes + TLV_LEN_SIZE +
			    TLV_TYPE_SIZE) > out_buf_len) {
				pr_err("%s: Too Small Buffer @DATA_LEN\n",
					__func__);
				return -ETOOSMALL;
			}
			rc = qmi_encode_basic_elem(buf_dst, &data_len_value,
						   1, data_len_sz);
			UPDATE_ENCODE_VARIABLES(temp_ei, buf_dst,
				encoded_bytes, tlv_len, encode_tlv, rc);
			if (!data_len_value)
				temp_ei = skip_to_next_elem(temp_ei, enc_level);
			else
				encode_tlv = 0;
			break;

		case QMI_UNSIGNED_1_BYTE:
		case QMI_UNSIGNED_2_BYTE:
		case QMI_UNSIGNED_4_BYTE:
		case QMI_UNSIGNED_8_BYTE:
		case QMI_SIGNED_2_BYTE_ENUM:
		case QMI_SIGNED_4_BYTE_ENUM:
			/* Check to avoid out of range buffer access */
			if (((data_len_value * temp_ei->elem_size) +
			    encoded_bytes + TLV_LEN_SIZE + TLV_TYPE_SIZE) >
			    out_buf_len) {
				pr_err("%s: Too Small Buffer @data_type:%d\n",
					__func__, temp_ei->data_type);
				return -ETOOSMALL;
			}
			rc = qmi_encode_basic_elem(buf_dst, buf_src,
				data_len_value, temp_ei->elem_size);
			QMI_ENCODE_LOG_ELEM(enc_level, data_len_value,
				temp_ei->elem_size, buf_src);
			UPDATE_ENCODE_VARIABLES(temp_ei, buf_dst,
				encoded_bytes, tlv_len, encode_tlv, rc);
			break;

		case QMI_STRUCT:
			rc = qmi_encode_struct_elem(temp_ei, buf_dst, buf_src,
				data_len_value, (out_buf_len - encoded_bytes),
				(enc_level + 1));
			if (rc < 0)
				return rc;
			UPDATE_ENCODE_VARIABLES(temp_ei, buf_dst,
				encoded_bytes, tlv_len, encode_tlv, rc);
			break;

		case QMI_STRING:
			rc = qmi_encode_string_elem(temp_ei, buf_dst, buf_src,
				out_buf_len - encoded_bytes, enc_level);
			if (rc < 0)
				return rc;
			UPDATE_ENCODE_VARIABLES(temp_ei, buf_dst,
				encoded_bytes, tlv_len, encode_tlv, rc);
			break;
		default:
			pr_err("%s: Unrecognized data type\n", __func__);
			return -EINVAL;

		}

		if (encode_tlv && enc_level == 1) {
			QMI_ENCDEC_ENCODE_TLV(tlv_type, tlv_len, tlv_pointer);
			QMI_ENCODE_LOG_TLV(tlv_type, tlv_len);
			encoded_bytes += (TLV_TYPE_SIZE + TLV_LEN_SIZE);
			tlv_pointer = buf_dst;
			tlv_len = 0;
			buf_dst = buf_dst + TLV_LEN_SIZE + TLV_TYPE_SIZE;
			encode_tlv = 0;
		}
	}
	QMI_ENCODE_LOG_MSG(out_buf, encoded_bytes);
	return encoded_bytes;
}

/**
 * qmi_kernel_decode() - Decode to C Structure format
 * @desc: Pointer to structure descriptor.
 * @out_c_struct: Buffer to hold the decoded C structure.
 * @in_buf: Buffer containg the QMI message to be decoded.
 * @in_buf_len: Length of the incoming QMI message.
 *
 * @return: 0 on success, < 0 on error.
 */
int qmi_kernel_decode(struct msg_desc *desc, void *out_c_struct,
		      void *in_buf, uint32_t in_buf_len)
{
	int dec_level = 1;
	int rc = 0;

	if (!desc || !desc->ei_array)
		return -EINVAL;

	if (!out_c_struct || !in_buf || !in_buf_len)
		return -EINVAL;

	if (desc->max_msg_len < in_buf_len)
		return -EINVAL;

	rc = _qmi_kernel_decode(desc->ei_array, out_c_struct,
				in_buf, in_buf_len, dec_level);
	if (rc < 0)
		return rc;
	else
		return 0;
}
EXPORT_SYMBOL(qmi_kernel_decode);

/**
 * qmi_decode_basic_elem() - Decodes elements of basic/primary data type
 * @buf_dst: Buffer to store the decoded element.
 * @buf_src: Buffer containing the elements in QMI wire format.
 * @elem_len: Number of elements to be decoded.
 * @elem_size: Size of a single instance of the element to be decoded.
 *
 * @return: Total size of the decoded data elements, in bytes.
 *
 * This function decodes the "elem_len" number of elements in QMI wire format,
 * each of size "elem_size" bytes from the source buffer "buf_src" and stores
 * the decoded elements in the destination buffer "buf_dst". The elements are
 * of primary data type which include uint8_t - uint64_t or similar. This
 * function returns the number of bytes of decoded information.
 */
static int qmi_decode_basic_elem(void *buf_dst, void *buf_src,
				 uint32_t elem_len, uint32_t elem_size)
{
	uint32_t i, rc = 0;

	for (i = 0; i < elem_len; i++) {
		QMI_ENCDEC_DECODE_N_BYTES(buf_dst, buf_src, elem_size);
		rc += elem_size;
	}

	return rc;
}

/**
 * qmi_decode_struct_elem() - Decodes elements of struct data type
 * @ei_array: Struct info array descibing the struct element.
 * @buf_dst: Buffer to store the decoded element.
 * @buf_src: Buffer containing the elements in QMI wire format.
 * @elem_len: Number of elements to be decoded.
 * @tlv_len: Total size of the encoded inforation corresponding to
 *           this struct element.
 * @dec_level: Depth of the nested structure from the main structure.
 *
 * @return: Total size of the decoded data elements, on success.
 *          < 0 on error.
 *
 * This function decodes the "elem_len" number of elements in QMI wire format,
 * each of size "(tlv_len/elem_len)" bytes from the source buffer "buf_src"
 * and stores the decoded elements in the destination buffer "buf_dst". The
 * elements are of struct data type which includes any C structure. This
 * function returns the number of bytes of decoded information.
 */
static int qmi_decode_struct_elem(struct elem_info *ei_array, void *buf_dst,
				  void *buf_src, uint32_t elem_len,
				  uint32_t tlv_len, int dec_level)
{
	int i, rc, decoded_bytes = 0;
	struct elem_info *temp_ei = ei_array;

	for (i = 0; i < elem_len && decoded_bytes < tlv_len; i++) {
		rc = _qmi_kernel_decode(temp_ei->ei_array, buf_dst, buf_src,
					(tlv_len - decoded_bytes), dec_level);
		if (rc < 0)
			return rc;
		buf_src = buf_src + rc;
		buf_dst = buf_dst + temp_ei->elem_size;
		decoded_bytes += rc;
	}

	if ((dec_level <= 2 && decoded_bytes != tlv_len) ||
	    (dec_level > 2 && (i < elem_len || decoded_bytes > tlv_len))) {
		pr_err("%s: Fault in decoding: dl(%d), db(%d), tl(%d), i(%d), el(%d)\n",
			__func__, dec_level, decoded_bytes, tlv_len,
			i, elem_len);
		return -EFAULT;
	}
	return decoded_bytes;
}

/**
 * qmi_decode_string_elem() - Decodes elements of string data type
 * @ei_array: Struct info array descibing the string element.
 * @buf_dst: Buffer to store the decoded element.
 * @buf_src: Buffer containing the elements in QMI wire format.
 * @tlv_len: Total size of the encoded inforation corresponding to
 *           this string element.
 * @dec_level: Depth of the string element from the main structure.
 *
 * @return: Total size of the decoded data elements, on success.
 *          < 0 on error.
 *
 * This function decodes the string element of maximum length
 * "ei_array->elem_len" from the source buffer "buf_src" and puts it into
 * the destination buffer "buf_dst". This function returns number of bytes
 * decoded from the input buffer.
 */
static int qmi_decode_string_elem(struct elem_info *ei_array, void *buf_dst,
				  void *buf_src, uint32_t tlv_len,
				  int dec_level)
{
	int rc;
	int decoded_bytes = 0;
	uint32_t string_len = 0;
	uint32_t string_len_sz = 0;
	struct elem_info *temp_ei = ei_array;

	if (dec_level == 1) {
		string_len = tlv_len;
	} else {
		string_len_sz = temp_ei->elem_len <= U8_MAX ?
				sizeof(uint8_t) : sizeof(uint16_t);
		rc = qmi_decode_basic_elem(&string_len, buf_src,
					   1, string_len_sz);
		decoded_bytes += rc;
	}

	if (string_len >= temp_ei->elem_len) {
		pr_err("%s: String len %d >= Max Len %d\n",
			__func__, string_len, temp_ei->elem_len);
		return -ETOOSMALL;
	} else if (string_len > tlv_len) {
		pr_err("%s: String len %d > Input Buffer Len %d\n",
			__func__, string_len, tlv_len);
		return -EFAULT;
	}

	rc = qmi_decode_basic_elem(buf_dst, buf_src + decoded_bytes,
				   string_len, temp_ei->elem_size);
	*((char *)buf_dst + string_len) = '\0';
	decoded_bytes += rc;
	QMI_DECODE_LOG_ELEM(dec_level, string_len, temp_ei->elem_size, buf_dst);
	return decoded_bytes;
}

/**
 * find_ei() - Find element info corresponding to TLV Type
 * @ei_array: Struct info array of the message being decoded.
 * @type: TLV Type of the element being searched.
 *
 * @return: Pointer to struct info, if found
 *
 * Every element that got encoded in the QMI message will have a type
 * information associated with it. While decoding the QMI message,
 * this function is used to find the struct info regarding the element
 * that corresponds to the type being decoded.
 */
static struct elem_info *find_ei(struct elem_info *ei_array,
				   uint32_t type)
{
	struct elem_info *temp_ei = ei_array;
	while (temp_ei->data_type != QMI_EOTI) {
		if (temp_ei->tlv_type == (uint8_t)type)
			return temp_ei;
		temp_ei = temp_ei + 1;
	}
	return NULL;
}

/**
 * _qmi_kernel_decode() - Core Decode Function
 * @ei_array: Struct info array describing the structure to be decoded.
 * @out_c_struct: Buffer to hold the decoded C struct
 * @in_buf: Buffer containing the QMI message to be decoded
 * @in_buf_len: Length of the QMI message to be decoded
 * @dec_level: Decode level to indicate the depth of the nested structure,
 *             within the main structure, being decoded
 *
 * @return: Number of bytes of decoded information, on success
 *          < 0 on error.
 */
static int _qmi_kernel_decode(struct elem_info *ei_array,
			      void *out_c_struct,
			      void *in_buf, uint32_t in_buf_len,
			      int dec_level)
{
	struct elem_info *temp_ei = ei_array;
	uint8_t opt_flag_value = 1;
	uint32_t data_len_value = 0, data_len_sz = 0;
	uint8_t *buf_dst = out_c_struct;
	uint8_t *tlv_pointer;
	uint32_t tlv_len = 0;
	uint32_t tlv_type;
	uint32_t decoded_bytes = 0;
	void *buf_src = in_buf;
	int rc;

	QMI_DECODE_LOG_MSG(in_buf, in_buf_len);
	while (decoded_bytes < in_buf_len) {
		if (dec_level >= 2 && temp_ei->data_type == QMI_EOTI)
			return decoded_bytes;

		if (dec_level == 1) {
			tlv_pointer = buf_src;
			QMI_ENCDEC_DECODE_TLV(&tlv_type,
					      &tlv_len, tlv_pointer);
			QMI_DECODE_LOG_TLV(tlv_type, tlv_len);
			buf_src += (TLV_TYPE_SIZE + TLV_LEN_SIZE);
			decoded_bytes += (TLV_TYPE_SIZE + TLV_LEN_SIZE);
			temp_ei = find_ei(ei_array, tlv_type);
			if (!temp_ei && (tlv_type < OPTIONAL_TLV_TYPE_START)) {
				pr_err("%s: Inval element info\n", __func__);
				return -EINVAL;
			} else if (!temp_ei) {
				UPDATE_DECODE_VARIABLES(buf_src,
						decoded_bytes, tlv_len);
				continue;
			}
		} else {
			/*
			 * No length information for elements in nested
			 * structures. So use remaining decodable buffer space.
			 */
			tlv_len = in_buf_len - decoded_bytes;
		}

		buf_dst = out_c_struct + temp_ei->offset;
		if (temp_ei->data_type == QMI_OPT_FLAG) {
			memcpy(buf_dst, &opt_flag_value, sizeof(uint8_t));
			temp_ei = temp_ei + 1;
			buf_dst = out_c_struct + temp_ei->offset;
		}

		if (temp_ei->data_type == QMI_DATA_LEN) {
			data_len_sz = temp_ei->elem_size == sizeof(uint8_t) ?
					sizeof(uint8_t) : sizeof(uint16_t);
			rc = qmi_decode_basic_elem(&data_len_value, buf_src,
						   1, data_len_sz);
			memcpy(buf_dst, &data_len_value, sizeof(uint32_t));
			temp_ei = temp_ei + 1;
			buf_dst = out_c_struct + temp_ei->offset;
			tlv_len -= data_len_sz;
			UPDATE_DECODE_VARIABLES(buf_src, decoded_bytes, rc);
		}

		if (temp_ei->is_array == NO_ARRAY) {
			data_len_value = 1;
		} else if (temp_ei->is_array == STATIC_ARRAY) {
			data_len_value = temp_ei->elem_len;
		} else if (data_len_value > temp_ei->elem_len) {
			pr_err("%s: Data len %d > max spec %d\n",
				__func__, data_len_value, temp_ei->elem_len);
			return -ETOOSMALL;
		}

		switch (temp_ei->data_type) {
		case QMI_UNSIGNED_1_BYTE:
		case QMI_UNSIGNED_2_BYTE:
		case QMI_UNSIGNED_4_BYTE:
		case QMI_UNSIGNED_8_BYTE:
		case QMI_SIGNED_2_BYTE_ENUM:
		case QMI_SIGNED_4_BYTE_ENUM:
			rc = qmi_decode_basic_elem(buf_dst, buf_src,
				data_len_value, temp_ei->elem_size);
			QMI_DECODE_LOG_ELEM(dec_level, data_len_value,
				temp_ei->elem_size, buf_dst);
			UPDATE_DECODE_VARIABLES(buf_src, decoded_bytes, rc);
			break;

		case QMI_STRUCT:
			rc = qmi_decode_struct_elem(temp_ei, buf_dst, buf_src,
				data_len_value, tlv_len, (dec_level + 1));
			if (rc < 0)
				return rc;
			UPDATE_DECODE_VARIABLES(buf_src, decoded_bytes, rc);
			break;

		case QMI_STRING:
			rc = qmi_decode_string_elem(temp_ei, buf_dst, buf_src,
						     tlv_len, dec_level);
			if (rc < 0)
				return rc;
			UPDATE_DECODE_VARIABLES(buf_src, decoded_bytes, rc);
			break;

		default:
			pr_err("%s: Unrecognized data type\n", __func__);
			return -EINVAL;
		}
		temp_ei = temp_ei + 1;
	}
	return decoded_bytes;
}
MODULE_DESCRIPTION("QMI kernel enc/dec");
MODULE_LICENSE("GPL v2");