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 /* SPDX-License-Identifier: GPL-2.0+ */
 /*
  * Surface Serial Hub (SSH) protocol and communication interface.
  *
  * Lower-level communication layers and SSH protocol definitions for the
  * Surface System Aggregator Module (SSAM). Provides the interface for basic
  * packet- and request-based communication with the SSAM EC via SSH.
  *
  * Copyright (C) 2019-2021 Maximilian Luz <luzmaximilian@gmail.com>
  */
 
 #ifndef _LINUX_SURFACE_AGGREGATOR_SERIAL_HUB_H
 #define _LINUX_SURFACE_AGGREGATOR_SERIAL_HUB_H
 
 #include <linux/crc-ccitt.h>
 #include <linux/kref.h>
 #include <linux/ktime.h>
 #include <linux/list.h>
 #include <linux/types.h>
 
 
 /* -- Data structures for SAM-over-SSH communication. ----------------------- */
 
 /**
  * enum ssh_frame_type - Frame types for SSH frames.
  *
  * @SSH_FRAME_TYPE_DATA_SEQ:
  *  Indicates a data frame, followed by a payload with the length specified
  *  in the ``struct ssh_frame.len`` field. This frame is sequenced, meaning
  *  that an ACK is required.
  *
  * @SSH_FRAME_TYPE_DATA_NSQ:
  *  Same as %SSH_FRAME_TYPE_DATA_SEQ, but unsequenced, meaning that the
  *  message does not have to be ACKed.
  *
  * @SSH_FRAME_TYPE_ACK:
  *  Indicates an ACK message.
  *
  * @SSH_FRAME_TYPE_NAK:
  *  Indicates an error response for previously sent frame. In general, this
  *  means that the frame and/or payload is malformed, e.g. a CRC is wrong.
  *  For command-type payloads, this can also mean that the command is
  *  invalid.
  */
 enum ssh_frame_type {
     SSH_FRAME_TYPE_DATA_SEQ = 0x80,
     SSH_FRAME_TYPE_DATA_NSQ = 0x00,
     SSH_FRAME_TYPE_ACK      = 0x40,
     SSH_FRAME_TYPE_NAK      = 0x04,
 };
 
 /**
  * struct ssh_frame - SSH communication frame.
  * @type: The type of the frame. See &enum ssh_frame_type.
  * @len:  The length of the frame payload directly following the CRC for this
  *        frame. Does not include the final CRC for that payload.
  * @seq:  The sequence number for this message/exchange.
  */
 struct ssh_frame {
     u8 type;
     __le16 len;
     u8 seq;
 } __packed;
 
 static_assert(sizeof(struct ssh_frame) == 4);
 
 /*
  * SSH_FRAME_MAX_PAYLOAD_SIZE - Maximum SSH frame payload length in bytes.
  *
  * This is the physical maximum length of the protocol. Implementations may
  * set a more constrained limit.
  */
 #define SSH_FRAME_MAX_PAYLOAD_SIZE  U16_MAX
 
 /**
  * enum ssh_payload_type - Type indicator for the SSH payload.
  * @SSH_PLD_TYPE_CMD: The payload is a command structure with optional command
  *                    payload.
  */
 enum ssh_payload_type {
     SSH_PLD_TYPE_CMD = 0x80,
 };
 
 /**
  * struct ssh_command - Payload of a command-type frame.
  * @type:    The type of the payload. See &enum ssh_payload_type. Should be
  *           SSH_PLD_TYPE_CMD for this struct.
  * @tc:      Command target category.
  * @tid_out: Output target ID. Should be zero if this an incoming (EC to host)
  *           message.
  * @tid_in:  Input target ID. Should be zero if this is an outgoing (host to
  *           EC) message.
  * @iid:     Instance ID.
  * @rqid:    Request ID. Used to match requests with responses and differentiate
  *           between responses and events.
  * @cid:     Command ID.
  */
 struct ssh_command {
     u8 type;
     u8 tc;
     u8 tid_out;
     u8 tid_in;
     u8 iid;
     __le16 rqid;
     u8 cid;
 } __packed;
 
 static_assert(sizeof(struct ssh_command) == 8);
 
 /*
  * SSH_COMMAND_MAX_PAYLOAD_SIZE - Maximum SSH command payload length in bytes.
  *
  * This is the physical maximum length of the protocol. Implementations may
  * set a more constrained limit.
  */
 #define SSH_COMMAND_MAX_PAYLOAD_SIZE \
     (SSH_FRAME_MAX_PAYLOAD_SIZE - sizeof(struct ssh_command))
 
 /*
  * SSH_MSG_LEN_BASE - Base-length of a SSH message.
  *
  * This is the minimum number of bytes required to form a message. The actual
  * message length is SSH_MSG_LEN_BASE plus the length of the frame payload.
  */
 #define SSH_MSG_LEN_BASE    (sizeof(struct ssh_frame) + 3ull * sizeof(u16))
 
 /*
  * SSH_MSG_LEN_CTRL - Length of a SSH control message.
  *
  * This is the length of a SSH control message, which is equal to a SSH
  * message without any payload.
  */
 #define SSH_MSG_LEN_CTRL    SSH_MSG_LEN_BASE
 
 /**
  * SSH_MESSAGE_LENGTH() - Compute length of SSH message.
  * @payload_size: Length of the payload inside the SSH frame.
  *
  * Return: Returns the length of a SSH message with payload of specified size.
  */
 #define SSH_MESSAGE_LENGTH(payload_size) (SSH_MSG_LEN_BASE + (payload_size))
 
 /**
  * SSH_COMMAND_MESSAGE_LENGTH() - Compute length of SSH command message.
  * @payload_size: Length of the command payload.
  *
  * Return: Returns the length of a SSH command message with command payload of
  * specified size.
  */
 #define SSH_COMMAND_MESSAGE_LENGTH(payload_size) \
     SSH_MESSAGE_LENGTH(sizeof(struct ssh_command) + (payload_size))
 
 /**
  * SSH_MSGOFFSET_FRAME() - Compute offset in SSH message to specified field in
  * frame.
  * @field: The field for which the offset should be computed.
  *
  * Return: Returns the offset of the specified &struct ssh_frame field in the
  * raw SSH message data as. Takes SYN bytes (u16) preceding the frame into
  * account.
  */
 #define SSH_MSGOFFSET_FRAME(field) \
     (sizeof(u16) + offsetof(struct ssh_frame, field))
 
 /**
  * SSH_MSGOFFSET_COMMAND() - Compute offset in SSH message to specified field
  * in command.
  * @field: The field for which the offset should be computed.
  *
  * Return: Returns the offset of the specified &struct ssh_command field in
  * the raw SSH message data. Takes SYN bytes (u16) preceding the frame and the
  * frame CRC (u16) between frame and command into account.
  */
 #define SSH_MSGOFFSET_COMMAND(field) \
     (2ull * sizeof(u16) + sizeof(struct ssh_frame) \
         + offsetof(struct ssh_command, field))
 
 /*
  * SSH_MSG_SYN - SSH message synchronization (SYN) bytes as u16.
  */
 #define SSH_MSG_SYN     ((u16)0x55aa)
 
 /**
  * ssh_crc() - Compute CRC for SSH messages.
  * @buf: The pointer pointing to the data for which the CRC should be computed.
  * @len: The length of the data for which the CRC should be computed.
  *
  * Return: Returns the CRC computed on the provided data, as used for SSH
  * messages.
  */
 static inline u16 ssh_crc(const u8 *buf, size_t len)
 {
     return crc_ccitt_false(0xffff, buf, len);
 }
 
 /*
  * SSH_NUM_EVENTS - The number of reserved event IDs.
  *
  * The number of reserved event IDs, used for registering an SSH event
  * handler. Valid event IDs are numbers below or equal to this value, with
  * exception of zero, which is not an event ID. Thus, this is also the
  * absolute maximum number of event handlers that can be registered.
  */
 #define SSH_NUM_EVENTS      38
 
 /*
  * SSH_NUM_TARGETS - The number of communication targets used in the protocol.
  */
 #define SSH_NUM_TARGETS     2
 
 /**
  * ssh_rqid_next_valid() - Return the next valid request ID.
  * @rqid: The current request ID.
  *
  * Return: Returns the next valid request ID, following the current request ID
  * provided to this function. This function skips any request IDs reserved for
  * events.
  */
 static inline u16 ssh_rqid_next_valid(u16 rqid)
 {
     return rqid > 0 ? rqid + 1u : rqid + SSH_NUM_EVENTS + 1u;
 }
 
 /**
  * ssh_rqid_to_event() - Convert request ID to its corresponding event ID.
  * @rqid: The request ID to convert.
  */
 static inline u16 ssh_rqid_to_event(u16 rqid)
 {
     return rqid - 1u;
 }
 
 /**
  * ssh_rqid_is_event() - Check if given request ID is a valid event ID.
  * @rqid: The request ID to check.
  */
 static inline bool ssh_rqid_is_event(u16 rqid)
 {
     return ssh_rqid_to_event(rqid) < SSH_NUM_EVENTS;
 }
 
 /**
  * ssh_tc_to_rqid() - Convert target category to its corresponding request ID.
  * @tc: The target category to convert.
  */
 static inline u16 ssh_tc_to_rqid(u8 tc)
 {
     return tc;
 }
 
 /**
  * ssh_tid_to_index() - Convert target ID to its corresponding target index.
  * @tid: The target ID to convert.
  */
 static inline u8 ssh_tid_to_index(u8 tid)
 {
     return tid - 1u;
 }
 
 /**
  * ssh_tid_is_valid() - Check if target ID is valid/supported.
  * @tid: The target ID to check.
  */
 static inline bool ssh_tid_is_valid(u8 tid)
 {
     return ssh_tid_to_index(tid) < SSH_NUM_TARGETS;
 }
 
 /**
  * struct ssam_span - Reference to a buffer region.
  * @ptr: Pointer to the buffer region.
  * @len: Length of the buffer region.
  *
  * A reference to a (non-owned) buffer segment, consisting of pointer and
  * length. Use of this struct indicates non-owned data, i.e. data of which the
  * life-time is managed (i.e. it is allocated/freed) via another pointer.
  */
 struct ssam_span {
     u8    *ptr;
     size_t len;
 };
 
 /*
  * Known SSH/EC target categories.
  *
  * List of currently known target category values; "Known" as in we know they
  * exist and are valid on at least some device/model. Detailed functionality
  * or the full category name is only known for some of these categories and
  * is detailed in the respective comment below.
  *
  * These values and abbreviations have been extracted from strings inside the
  * Windows driver.
  */
 enum ssam_ssh_tc {
                   /* Category 0x00 is invalid for EC use. */
     SSAM_SSH_TC_SAM  = 0x01,  /* Generic system functionality, real-time clock. */
     SSAM_SSH_TC_BAT  = 0x02,  /* Battery/power subsystem. */
     SSAM_SSH_TC_TMP  = 0x03,  /* Thermal subsystem. */
     SSAM_SSH_TC_PMC  = 0x04,
     SSAM_SSH_TC_FAN  = 0x05,
     SSAM_SSH_TC_PoM  = 0x06,
     SSAM_SSH_TC_DBG  = 0x07,
     SSAM_SSH_TC_KBD  = 0x08,  /* Legacy keyboard (Laptop 1/2). */
     SSAM_SSH_TC_FWU  = 0x09,
     SSAM_SSH_TC_UNI  = 0x0a,
     SSAM_SSH_TC_LPC  = 0x0b,
     SSAM_SSH_TC_TCL  = 0x0c,
     SSAM_SSH_TC_SFL  = 0x0d,
     SSAM_SSH_TC_KIP  = 0x0e,  /* Manages detachable peripherals (Pro X/8 keyboard cover) */
     SSAM_SSH_TC_EXT  = 0x0f,
     SSAM_SSH_TC_BLD  = 0x10,
     SSAM_SSH_TC_BAS  = 0x11,  /* Detachment system (Surface Book 2/3). */
     SSAM_SSH_TC_SEN  = 0x12,
     SSAM_SSH_TC_SRQ  = 0x13,
     SSAM_SSH_TC_MCU  = 0x14,
     SSAM_SSH_TC_HID  = 0x15,  /* Generic HID input subsystem. */
     SSAM_SSH_TC_TCH  = 0x16,
     SSAM_SSH_TC_BKL  = 0x17,
     SSAM_SSH_TC_TAM  = 0x18,
     SSAM_SSH_TC_ACC0 = 0x19,
     SSAM_SSH_TC_UFI  = 0x1a,
     SSAM_SSH_TC_USC  = 0x1b,
     SSAM_SSH_TC_PEN  = 0x1c,
     SSAM_SSH_TC_VID  = 0x1d,
     SSAM_SSH_TC_AUD  = 0x1e,
     SSAM_SSH_TC_SMC  = 0x1f,
     SSAM_SSH_TC_KPD  = 0x20,
     SSAM_SSH_TC_REG  = 0x21,  /* Extended event registry. */
     SSAM_SSH_TC_SPT  = 0x22,
     SSAM_SSH_TC_SYS  = 0x23,
     SSAM_SSH_TC_ACC1 = 0x24,
     SSAM_SSH_TC_SHB  = 0x25,
     SSAM_SSH_TC_POS  = 0x26,  /* For obtaining Laptop Studio screen position. */
 };
 
 
 /* -- Packet transport layer (ptl). ----------------------------------------- */
 
 /**
  * enum ssh_packet_base_priority - Base priorities for &struct ssh_packet.
  * @SSH_PACKET_PRIORITY_FLUSH: Base priority for flush packets.
  * @SSH_PACKET_PRIORITY_DATA:  Base priority for normal data packets.
  * @SSH_PACKET_PRIORITY_NAK:   Base priority for NAK packets.
  * @SSH_PACKET_PRIORITY_ACK:   Base priority for ACK packets.
  */
 enum ssh_packet_base_priority {
     SSH_PACKET_PRIORITY_FLUSH = 0,  /* same as DATA to sequence flush */
     SSH_PACKET_PRIORITY_DATA  = 0,
     SSH_PACKET_PRIORITY_NAK   = 1,
     SSH_PACKET_PRIORITY_ACK   = 2,
 };
 
 /*
  * Same as SSH_PACKET_PRIORITY() below, only with actual values.
  */
 #define __SSH_PACKET_PRIORITY(base, try) \
     (((base) << 4) | ((try) & 0x0f))
 
 /**
  * SSH_PACKET_PRIORITY() - Compute packet priority from base priority and
  * number of tries.
  * @base: The base priority as suffix of &enum ssh_packet_base_priority, e.g.
  *        ``FLUSH``, ``DATA``, ``ACK``, or ``NAK``.
  * @try:  The number of tries (must be less than 16).
  *
  * Compute the combined packet priority. The combined priority is dominated by
  * the base priority, whereas the number of (re-)tries decides the precedence
  * of packets with the same base priority, giving higher priority to packets
  * that already have more tries.
  *
  * Return: Returns the computed priority as value fitting inside a &u8. A
  * higher number means a higher priority.
  */
 #define SSH_PACKET_PRIORITY(base, try) \
     __SSH_PACKET_PRIORITY(SSH_PACKET_PRIORITY_##base, (try))
 
 /**
  * ssh_packet_priority_get_try() - Get number of tries from packet priority.
  * @priority: The packet priority.
  *
  * Return: Returns the number of tries encoded in the specified packet
  * priority.
  */
 static inline u8 ssh_packet_priority_get_try(u8 priority)
 {
     return priority & 0x0f;
 }
 
 /**
  * ssh_packet_priority_get_base - Get base priority from packet priority.
  * @priority: The packet priority.
  *
  * Return: Returns the base priority encoded in the given packet priority.
  */
 static inline u8 ssh_packet_priority_get_base(u8 priority)
 {
     return (priority & 0xf0) >> 4;
 }
 
 enum ssh_packet_flags {
     /* state flags */
     SSH_PACKET_SF_LOCKED_BIT,
     SSH_PACKET_SF_QUEUED_BIT,
     SSH_PACKET_SF_PENDING_BIT,
     SSH_PACKET_SF_TRANSMITTING_BIT,
     SSH_PACKET_SF_TRANSMITTED_BIT,
     SSH_PACKET_SF_ACKED_BIT,
     SSH_PACKET_SF_CANCELED_BIT,
     SSH_PACKET_SF_COMPLETED_BIT,
 
     /* type flags */
     SSH_PACKET_TY_FLUSH_BIT,
     SSH_PACKET_TY_SEQUENCED_BIT,
     SSH_PACKET_TY_BLOCKING_BIT,
 
     /* mask for state flags */
     SSH_PACKET_FLAGS_SF_MASK =
           BIT(SSH_PACKET_SF_LOCKED_BIT)
         | BIT(SSH_PACKET_SF_QUEUED_BIT)
         | BIT(SSH_PACKET_SF_PENDING_BIT)
         | BIT(SSH_PACKET_SF_TRANSMITTING_BIT)
         | BIT(SSH_PACKET_SF_TRANSMITTED_BIT)
         | BIT(SSH_PACKET_SF_ACKED_BIT)
         | BIT(SSH_PACKET_SF_CANCELED_BIT)
         | BIT(SSH_PACKET_SF_COMPLETED_BIT),
 
     /* mask for type flags */
     SSH_PACKET_FLAGS_TY_MASK =
           BIT(SSH_PACKET_TY_FLUSH_BIT)
         | BIT(SSH_PACKET_TY_SEQUENCED_BIT)
         | BIT(SSH_PACKET_TY_BLOCKING_BIT),
 };
 
 struct ssh_ptl;
 struct ssh_packet;
 
 /**
  * struct ssh_packet_ops - Callback operations for a SSH packet.
  * @release:  Function called when the packet reference count reaches zero.
  *            This callback must be relied upon to ensure that the packet has
  *            left the transport system(s).
  * @complete: Function called when the packet is completed, either with
  *            success or failure. In case of failure, the reason for the
  *            failure is indicated by the value of the provided status code
  *            argument. This value will be zero in case of success. Note that
  *            a call to this callback does not guarantee that the packet is
  *            not in use by the transport system any more.
  */
 struct ssh_packet_ops {
     void (*release)(struct ssh_packet *p);
     void (*complete)(struct ssh_packet *p, int status);
 };
 
 /**
  * struct ssh_packet - SSH transport packet.
  * @ptl:      Pointer to the packet transport layer. May be %NULL if the packet
  *            (or enclosing request) has not been submitted yet.
  * @refcnt:   Reference count of the packet.
  * @priority: Priority of the packet. Must be computed via
  *            SSH_PACKET_PRIORITY(). Must only be accessed while holding the
  *            queue lock after first submission.
  * @data:     Raw message data.
  * @data.len: Length of the raw message data.
  * @data.ptr: Pointer to the raw message data buffer.
  * @state:    State and type flags describing current packet state (dynamic)
  *            and type (static). See &enum ssh_packet_flags for possible
  *            options.
  * @timestamp: Timestamp specifying when the latest transmission of a
  *            currently pending packet has been started. May be %KTIME_MAX
  *            before or in-between transmission attempts. Used for the packet
  *            timeout implementation. Must only be accessed while holding the
  *            pending lock after first submission.
  * @queue_node: The list node for the packet queue.
  * @pending_node: The list node for the set of pending packets.
  * @ops:      Packet operations.
  */
 struct ssh_packet {
     struct ssh_ptl *ptl;
     struct kref refcnt;
 
     u8 priority;
 
     struct {
         size_t len;
         u8 *ptr;
     } data;
 
     unsigned long state;
     ktime_t timestamp;
 
     struct list_head queue_node;
     struct list_head pending_node;
 
     const struct ssh_packet_ops *ops;
 };
 
 struct ssh_packet *ssh_packet_get(struct ssh_packet *p);
 void ssh_packet_put(struct ssh_packet *p);
 
 /**
  * ssh_packet_set_data() - Set raw message data of packet.
  * @p:   The packet for which the message data should be set.
  * @ptr: Pointer to the memory holding the message data.
  * @len: Length of the message data.
  *
  * Sets the raw message data buffer of the packet to the provided memory. The
  * memory is not copied. Instead, the caller is responsible for management
  * (i.e. allocation and deallocation) of the memory. The caller must ensure
  * that the provided memory is valid and contains a valid SSH message,
  * starting from the time of submission of the packet until the ``release``
  * callback has been called. During this time, the memory may not be altered
  * in any way.
  */
 static inline void ssh_packet_set_data(struct ssh_packet *p, u8 *ptr, size_t len)
 {
     p->data.ptr = ptr;
     p->data.len = len;
 }
 
 
 /* -- Request transport layer (rtl). ---------------------------------------- */
 
 enum ssh_request_flags {
     /* state flags */
     SSH_REQUEST_SF_LOCKED_BIT,
     SSH_REQUEST_SF_QUEUED_BIT,
     SSH_REQUEST_SF_PENDING_BIT,
     SSH_REQUEST_SF_TRANSMITTING_BIT,
     SSH_REQUEST_SF_TRANSMITTED_BIT,
     SSH_REQUEST_SF_RSPRCVD_BIT,
     SSH_REQUEST_SF_CANCELED_BIT,
     SSH_REQUEST_SF_COMPLETED_BIT,
 
     /* type flags */
     SSH_REQUEST_TY_FLUSH_BIT,
     SSH_REQUEST_TY_HAS_RESPONSE_BIT,
 
     /* mask for state flags */
     SSH_REQUEST_FLAGS_SF_MASK =
           BIT(SSH_REQUEST_SF_LOCKED_BIT)
         | BIT(SSH_REQUEST_SF_QUEUED_BIT)
         | BIT(SSH_REQUEST_SF_PENDING_BIT)
         | BIT(SSH_REQUEST_SF_TRANSMITTING_BIT)
         | BIT(SSH_REQUEST_SF_TRANSMITTED_BIT)
         | BIT(SSH_REQUEST_SF_RSPRCVD_BIT)
         | BIT(SSH_REQUEST_SF_CANCELED_BIT)
         | BIT(SSH_REQUEST_SF_COMPLETED_BIT),
 
     /* mask for type flags */
     SSH_REQUEST_FLAGS_TY_MASK =
           BIT(SSH_REQUEST_TY_FLUSH_BIT)
         | BIT(SSH_REQUEST_TY_HAS_RESPONSE_BIT),
 };
 
 struct ssh_rtl;
 struct ssh_request;
 
 /**
  * struct ssh_request_ops - Callback operations for a SSH request.
  * @release:  Function called when the request's reference count reaches zero.
  *            This callback must be relied upon to ensure that the request has
  *            left the transport systems (both, packet an request systems).
  * @complete: Function called when the request is completed, either with
  *            success or failure. The command data for the request response
  *            is provided via the &struct ssh_command parameter (``cmd``),
  *            the command payload of the request response via the &struct
  *            ssh_span parameter (``data``).
  *
  *            If the request does not have any response or has not been
  *            completed with success, both ``cmd`` and ``data`` parameters will
  *            be NULL. If the request response does not have any command
  *            payload, the ``data`` span will be an empty (zero-length) span.
  *
  *            In case of failure, the reason for the failure is indicated by
  *            the value of the provided status code argument (``status``). This
  *            value will be zero in case of success and a regular errno
  *            otherwise.
  *
  *            Note that a call to this callback does not guarantee that the
  *            request is not in use by the transport systems any more.
  */
 struct ssh_request_ops {
     void (*release)(struct ssh_request *rqst);
     void (*complete)(struct ssh_request *rqst,
              const struct ssh_command *cmd,
              const struct ssam_span *data, int status);
 };
 
 /**
  * struct ssh_request - SSH transport request.
  * @packet: The underlying SSH transport packet.
  * @node:   List node for the request queue and pending set.
  * @state:  State and type flags describing current request state (dynamic)
  *          and type (static). See &enum ssh_request_flags for possible
  *          options.
  * @timestamp: Timestamp specifying when we start waiting on the response of
  *          the request. This is set once the underlying packet has been
  *          completed and may be %KTIME_MAX before that, or when the request
  *          does not expect a response. Used for the request timeout
  *          implementation.
  * @ops:    Request Operations.
  */
 struct ssh_request {
     struct ssh_packet packet;
     struct list_head node;
 
     unsigned long state;
     ktime_t timestamp;
 
     const struct ssh_request_ops *ops;
 };
 
 /**
  * to_ssh_request() - Cast a SSH packet to its enclosing SSH request.
  * @p: The packet to cast.
  *
  * Casts the given &struct ssh_packet to its enclosing &struct ssh_request.
  * The caller is responsible for making sure that the packet is actually
  * wrapped in a &struct ssh_request.
  *
  * Return: Returns the &struct ssh_request wrapping the provided packet.
  */
 static inline struct ssh_request *to_ssh_request(struct ssh_packet *p)
 {
     return container_of(p, struct ssh_request, packet);
 }
 
 /**
  * ssh_request_get() - Increment reference count of request.
  * @r: The request to increment the reference count of.
  *
  * Increments the reference count of the given request by incrementing the
  * reference count of the underlying &struct ssh_packet, enclosed in it.
  *
  * See also ssh_request_put(), ssh_packet_get().
  *
  * Return: Returns the request provided as input.
  */
 static inline struct ssh_request *ssh_request_get(struct ssh_request *r)
 {
     return r ? to_ssh_request(ssh_packet_get(&r->packet)) : NULL;
 }
 
 /**
  * ssh_request_put() - Decrement reference count of request.
  * @r: The request to decrement the reference count of.
  *
  * Decrements the reference count of the given request by decrementing the
  * reference count of the underlying &struct ssh_packet, enclosed in it. If
  * the reference count reaches zero, the ``release`` callback specified in the
  * request's &struct ssh_request_ops, i.e. ``r->ops->release``, will be
  * called.
  *
  * See also ssh_request_get(), ssh_packet_put().
  */
 static inline void ssh_request_put(struct ssh_request *r)
 {
     if (r)
         ssh_packet_put(&r->packet);
 }
 
 /**
  * ssh_request_set_data() - Set raw message data of request.
  * @r:   The request for which the message data should be set.
  * @ptr: Pointer to the memory holding the message data.
  * @len: Length of the message data.
  *
  * Sets the raw message data buffer of the underlying packet to the specified
  * buffer. Does not copy the actual message data, just sets the buffer pointer
  * and length. Refer to ssh_packet_set_data() for more details.
  */
 static inline void ssh_request_set_data(struct ssh_request *r, u8 *ptr, size_t len)
 {
     ssh_packet_set_data(&r->packet, ptr, len);
 }
 
 #endif /* _LINUX_SURFACE_AGGREGATOR_SERIAL_HUB_H */

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