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msm: qmi: Add QMI documentation
Add documentation for the MSM QMI library. Change-Id: I95702c19d3d871af47e0e6d1af6d544b3f85e723 Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>
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Documentation/arm/msm/msm_qmi.txt
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Documentation/arm/msm/msm_qmi.txt
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Introduction
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============
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Qualcomm MSM Interface(QMI) is a messaging format used to communicate
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between software components in the modem and other peripheral subsystems.
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This document proposes an architecture to introduce the QMI messaging
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into the kernel. This document proposes introducing a QMI encode/decode
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library to enable QMI message marshaling and an interface library to enable
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sending and receiving QMI messages through MSM IPC Router.
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Hardware description
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====================
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QMI is a messaging format used to interface with the components in modem
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and other subsystems. QMI does not drive or manage any hardware resources.
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Software description
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====================
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QMI communication is based on a client-server model, where clients and
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servers exchange messages in QMI wire format. A module can act as a client
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of any number of QMI services and a QMI service can serve any number of
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clients.
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QMI communication is of request/response type or an unsolicited event type.
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QMI client driver sends a request to a QMI service and receives a response.
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QMI client driver registers with the QMI service to receive indications
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regarding a system event and the QMI service sends the indications to the
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client when the event occurs in the system.
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The wire format of QMI message is as follows:
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----------------------------------------------------
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| QMI Header | TLV 0 | TLV 1 | ... | TLV N |
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----------------------------------------------------
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QMI Header:
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-----------
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--------------------------------------------------------
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| Flags | Transaction ID | Message ID | Message Length |
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--------------------------------------------------------
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The flags field is used to indicate the kind of QMI message - request,
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response or indication. The transaction ID is a client specific field
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to uniquely match the QMI request and the response. The message ID is
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also a client specific field to indicate the kind of information present
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in the QMI payload. The message length field holds the size information
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of the QMI payload.
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Flags:
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------
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* 0 - QMI Request
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* 2 - QMI Response
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* 4 - QMI Indication
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TLV:
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----
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QMI payload is represented using a series of Type, Length and Value fields.
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Each information being passed is encoded into a type, length and value
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combination. The type element identifies the type of information being
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encoded. The length element specifies the length of the information/values
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being encoded. The information can be of a primitive type or a structure
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or an array.
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-------------------------------------------
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| Type | Length | Value 0 | ... | Value N |
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-------------------------------------------
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QMI Message Marshaling and Transport:
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-------------------------------------
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QMI encode/decode library is designed to encode the kernel C data
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structures into QMI wire format and to decode the QMI messages into kernel
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C data strcuture format. This library will provide a single interface to
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transform any data structure into a QMI message and vice-versa.
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QMI interface library is designed to send and receive QMI messages over
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IPC Router.
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----------------------------------
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| Kernel Drivers |
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----------------------------------
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| |
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| |
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----------------- -----------------
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| QMI Interface |___| QMI Enc/Dec |
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| Library | | Library |
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----------------- -----------------
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|
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|
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-------------------
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| IPC Message |
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| Router |
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-------------------
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|
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-------
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| SMD |
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-------
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Design
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======
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The design goals of this proposed QMI messaging mechanism are:
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* To enable QMI messaging from within the kernel
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* To provide a common library to marshal QMI messages
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* To provide a common interface library to send/receive QMI messages
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* To support kernel QMI clients which have latency constraints
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The reason behind this design decision is:
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* To provide a simple QMI marshaling interface to the kernel users
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* To hide the complexities of QMI message transports
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* To minimize code redundancy
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In order to provide a single encode/decode API, the library expects
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the kernel drivers to pass the:
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* starting address of the data structure to be encoded/decoded
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* starting address of the QMI message buffer
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* a table containing information regarding the data structure to
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be encoded/decoded
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The design is based on the idea that any complex data structure is a
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collection of primary data elements. Hence the information about any
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data structure can be constructed as an array of information about its
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primary data elements. The following structure is defined to describe
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information about a primary data element.
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/**
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* elem_info - Data structure to specify information about an element
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* in a data structure. An array of this data structure
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* can be used to specify info about a complex data
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* structure to be encoded/decoded.
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* @data_type: Data type of this element
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* @elem_len: Array length of this element, if an array
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* @elem_size: Size of a single instance of this data type
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* @is_array: Array type of this element
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* @tlv_type: QMI message specific type to identify which element
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* is present in an incoming message
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* @offset: To identify the address of the first instance of this
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* element in the data structure
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* @ei_array: Array to provide information about the nested structure
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* within a data structure to be encoded/decoded.
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*/
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struct elem_info {
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enum elem_type data_type;
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uint32_t elem_len;
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uint32_t elem_size;
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enum array_type is_array;
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uint8_t tlv_type;
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uint32_t offset;
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struct elem_info *ei_array;
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};
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The alternate design discussions include manual encoding/decoding of QMI
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messages. From RPC experience, this approach has mostly been error prone.
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This in turn lead to increased development and debugging effort. Another
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approach included data-structure specific marshaling API -- i.e. every
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data structure to be encoded/decoded should have a unique auto-generated
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marshaling API. This approach comes with the cost of code redundancy and
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was therefore rejected.
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Power Management
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================
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N/A
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SMP/multi-core
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==============
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The QMI encode/decode library does not access any global or shared data
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structures. Hence it does not require any locking mechanisms to ensure
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multi-core safety.
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The QMI interface library uses mutexes while accessing shared resources.
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Security
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========
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N/A
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Performance
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===========
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This design proposal is to support kernel QMI clients which have latency
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constraints. Hence the number and size of QMI messages are expected to be
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kept short, in order to achieve latency of less than 1 ms consistently.
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Interface
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=========
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Kernel-APIs:
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------------
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Encode/Decode Library APIs:
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---------------------------
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/**
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* elem_type - Enum to identify the data type of elements in a data
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* structure.
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*/
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enum elem_type {
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QMI_OPT_FLAG = 1,
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QMI_DATA_LEN,
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QMI_UNSIGNED_1_BYTE,
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QMI_UNSIGNED_2_BYTE,
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QMI_UNSIGNED_4_BYTE,
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QMI_UNSIGNED_8_BYTE,
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QMI_SIGNED_2_BYTE_ENUM,
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QMI_SIGNED_4_BYTE_ENUM,
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QMI_STRUCT,
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QMI_END_OF_TYPE_INFO,
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};
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/**
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* array_type - Enum to identify if an element in a data structure is
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* an array. If so, then is it a static length array or a
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* variable length array.
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*/
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enum array_type {
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NO_ARRAY = 0,
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STATIC_ARRAY = 1,
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VAR_LEN_ARRAY = 2,
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};
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/**
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* msg_desc - Describe about the main/outer structure to be
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* encoded/decoded.
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* @msg_id: Message ID to identify the kind of QMI message.
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* @max_msg_len: Maximum possible length of the QMI message.
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* @ei_array: Array to provide information about a data structure.
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*/
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struct msg_desc {
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uint16_t msg_id;
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int max_msg_len;
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struct elem_info *ei_array;
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};
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/**
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* qmi_kernel_encode() - Encode to QMI message wire format
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* @desc: Structure describing the data structure to be encoded.
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* @out_buf: Buffer to hold the encoded QMI message.
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* @out_buf_len: Length of the buffer to hold the QMI message.
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* @in_c_struct: C Structure to be encoded.
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*
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* @return: size of encoded message on success,
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* -ve value on failure.
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*/
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int qmi_kernel_encode(struct msg_desc *desc,
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void *out_buf, uint32_t out_buf_len,
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void *in_c_struct);
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/**
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* qmi_kernel_decode() - Decode to C Structure format
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* @desc: Structure describing the data structure format.
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* @out_c_struct: Buffer to hold the decoded C structure.
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* @in_buf: Buffer containg the QMI message to be decoded.
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* @in_buf_len: Length of the incoming QMI message.
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*
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* @return: 0 on success, -ve value on failure.
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*/
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int qmi_kernel_decode(struct msg_desc *desc, void *out_c_struct,
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void *in_buf, uint32_t in_buf_len);
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Interface Library APIs:
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-----------------------
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/**
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* qmi_svc_event_notifier_register() - Register a notifier block to receive
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* events regarding a QMI service
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* @service_id: Service ID to identify the QMI service.
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* @instance_id: Instance ID to identify the instance of the QMI service.
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* @nb: Notifier block used to receive the event.
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*
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* @return: 0 if successfully registered, < 0 on error.
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*/
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int qmi_svc_event_notifier_register(uint32_t service_id,
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uint32_t instance_id,
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struct notifier_block *nb);
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/**
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* qmi_handle_create() - Create a QMI handle
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* @notify: Callback to notify events on the handle created.
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* @notify_priv: Private info to be passed along with the notification.
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*
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* @return: Valid QMI handle on success, NULL on error.
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*/
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struct qmi_handle *qmi_handle_create(
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void (*notify)(struct qmi_handle *handle,
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enum qmi_event_type event, void *notify_priv),
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void *notify_priv);
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/**
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* qmi_connect_to_service() - Connect the QMI handle with a QMI service
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* @handle: QMI handle to be connected with the QMI service.
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* @service_id: Service id to identify the QMI service.
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* @instance_id: Instance id to identify the instance of the QMI service.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_connect_to_service(struct qmi_handle *handle,
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uint32_t service_id, uint32_t instance_id);
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/**
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* qmi_register_ind_cb() - Register the indication callback function
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* @handle: QMI handle with which the function is registered.
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* @ind_cb: Callback function to be registered.
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* @ind_cb_priv: Private data to be passed with the indication callback.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_register_ind_cb(struct qmi_handle *handle,
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void (*ind_cb)(struct qmi_handle *handle,
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unsigned int msg_id, void *msg,
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unsigned int msg_len, void *ind_cb_priv),
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void *ind_cb_priv);
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/**
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* qmi_send_req_wait() - Send a synchronous QMI request
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* @handle: QMI handle through which the QMI request is sent.
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* @req_desc: Structure describing the request data structure.
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* @req: Buffer containing the request data structure.
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* @req_len: Length of the request data structure.
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* @resp_desc: Structure describing the response data structure.
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* @resp: Buffer to hold the response data structure.
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* @resp_len: Length of the response data structure.
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* @timeout_ms: Timeout before a response is received.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_send_req_wait(struct qmi_handle *handle,
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struct msg_desc *req_desc,
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void *req, unsigned int req_len,
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struct msg_desc *resp_desc,
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void *resp, unsigned int resp_len,
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unsigned long timeout_ms);
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/**
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* qmi_send_req_nowait() - Send an asynchronous QMI request
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* @handle: QMI handle through which the QMI request is sent.
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* @req_desc: Structure describing the request data structure.
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* @req: Buffer containing the request data structure.
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* @req_len: Length of the request data structure.
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* @resp_desc: Structure describing the response data structure.
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* @resp: Buffer to hold the response data structure.
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* @resp_len: Length of the response data structure.
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* @resp_cb: Callback function to be invoked when the response arrives.
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* @resp_cb_data: Private information to be passed along with the callback.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_send_req_nowait(struct qmi_handle *handle,
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struct msg_desc *req_desc,
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void *req, unsigned int req_len,
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struct msg_desc *resp_desc,
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void *resp, unsigned int resp_len,
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void (*resp_cb)(struct qmi_handle *handle,
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unsigned int msg_id, void *msg,
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void *resp_cb_data),
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void *resp_cb_data);
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/**
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* qmi_recv_msg() - Receive the QMI message
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* @handle: Handle for which the QMI message has to be received.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_recv_msg(struct qmi_handle *handle);
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/**
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* qmi_handle_destroy() - Destroy the QMI handle
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* @handle: QMI handle to be destroyed.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_handle_destroy(struct qmi_handle *handle);
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/**
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* qmi_svc_event_notifier_unregister() - Unregister service event notifier block
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* @service_id: Service ID to identify the QMI service.
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* @instance_id: Instance ID to identify the instance of the QMI service.
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* @nb: Notifier block registered to receive the events.
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*
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* @return: 0 if successfully registered, < 0 on error.
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*/
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int qmi_svc_event_notifier_unregister(uint32_t service_id,
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uint32_t instance_id,
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struct notifier_block *nb);
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/**
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* qmi_svc_ops_options - Operations and options to be specified when
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* a service registers.
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* @version: Version field to identify the ops_options structure.
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* @service_id: Service ID of the service being registered.
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* @instance_id: Instance ID of the service being registered.
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* @connect_cb: Callback when a new client connects with the service.
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* @disconnect_cb: Callback when the client exits the connection.
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* @req_desc_cb: Callback to get request structure and its descriptor
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* for a message id.
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* @req_cb: Callback to process the request.
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*/
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struct qmi_svc_ops_options {
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unsigned version;
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uint32_t service_id;
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uint32_t instance_id;
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int (*connect_cb)(struct qmi_handle *handle,
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struct qmi_svc_clnt *clnt);
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int (*disconnect_cb)(struct qmi_handle *handle,
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struct qmi_svc_clnt *clnt);
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struct msg_desc *(*req_desc_cb)(unsigned int msg_id,
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void **req,
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unsigned int req_len);
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int (*req_cb)(struct qmi_handle *handle,
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struct qmi_svc_clnt *clnt,
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void *req_handle,
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unsigned int msg_id,
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void *req);
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};
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/**
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* qmi_svc_register() - Register a QMI service with a QMI handle
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* @handle: QMI handle on which the service has to be registered.
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* @ops_options: Service specific operations and options.
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*
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* @return: 0 if successfully registered, < 0 on error.
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*/
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int qmi_svc_register(struct qmi_handle *handle,
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void *ops_options);
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/**
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* qmi_send_resp() - Send response to a request
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* @handle: QMI handle from which the response is sent.
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* @clnt: Client to which the response is sent.
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* @req_handle: Request for which the response is sent.
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* @resp_desc: Descriptor explaining the response structure.
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* @resp: Pointer to the response structure.
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* @resp_len: Length of the response structure.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_send_resp(struct qmi_handle *handle,
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struct qmi_svc_clnt *clnt,
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void *req_handle,
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struct msg_desc *resp_desc,
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void *resp,
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unsigned int resp_len);
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/**
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* qmi_send_ind() - Send unsolicited event/indication to a client
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* @handle: QMI handle from which the indication is sent.
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* @clnt: Client to which the indication is sent.
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* @ind_desc: Descriptor explaining the indication structure.
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* @ind: Pointer to the indication structure.
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* @ind_len: Length of the indication structure.
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*
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* @return: 0 on success, < 0 on error.
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*/
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int qmi_send_ind(struct qmi_handle *handle,
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struct qmi_svc_clnt *clnt,
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struct msg_desc *ind_desc,
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void *ind,
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unsigned int ind_len);
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/**
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* qmi_svc_unregister() - Unregister the service from a QMI handle
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* @handle: QMI handle from which the service has to be unregistered.
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*
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* return: 0 on success, < 0 on error.
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*/
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int qmi_svc_unregister(struct qmi_handle *handle);
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User-space APIs:
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----------------
|
||||
This proposal is meant only for kernel QMI clients/services and hence no
|
||||
user-space interface is defined as part of this proposal.
|
||||
|
||||
Driver parameters
|
||||
=================
|
||||
|
||||
N/A
|
||||
|
||||
Config options
|
||||
==============
|
||||
|
||||
The QMI encode/decode library will be enabled by default in the kernel.
|
||||
It can be disabled using CONFIG_QMI_ENCDEC kernel config option.
|
||||
|
||||
The QMI Interface library will be disabled by default in the kernel,
|
||||
since it depends on other components which are disabled by dafault.
|
||||
It can be enabled using CONFIG_MSM_QMI_INTERFACE kernel config option.
|
||||
|
||||
Dependencies
|
||||
============
|
||||
|
||||
The QMI encode/decode library is a stand-alone module and is not
|
||||
dependent on any other kernel modules.
|
||||
|
||||
The QMI Interface library depends on QMI Encode/Decode library and
|
||||
IPC Message Router.
|
||||
|
||||
User space utilities
|
||||
====================
|
||||
|
||||
N/A
|
||||
|
||||
Other
|
||||
=====
|
||||
|
||||
N/A
|
||||
|
||||
Known issues
|
||||
============
|
||||
|
||||
N/A
|
||||
|
||||
To do
|
||||
=====
|
||||
|
||||
Look into the possibility of making QMI Interface Library transport
|
||||
agnostic. This may involve the kernel drivers to register the transport,
|
||||
with the QMI Interface Library, to be used for transporting QMI messages.
|
Loading…
Reference in a new issue