153 lines
6.1 KiB
Plaintext
153 lines
6.1 KiB
Plaintext
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Introduction
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============
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The BAM data mux (bam_dmux) is a kernel module that facilitates
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communication between the existing RMNET driver and the Bus Access
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Manager (BAM) driver for LTE data connections.
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Software description
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====================
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The bam_dmux will follow the design and implementation of the sdio_dmux
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(already present in older platforms) and provide identical functionality
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where applicable.
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The bam_dmux driver will consist of a small transport abstraction layer
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for RMNET in drivers/net/ and the core functionality will exist in
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drivers/soc/qcom/. The core functionality of the bam_dmux module is
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to mux one bam channel into eight logical channels for use by RMNET.
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-------------------------------------------------
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| IP Framework |
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-------------------------------------------------
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| Rmnet | Rmnet | | Rmnet | Rmnet |
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| Dev 0 | Dev 1 | ... | Dev 6 | Dev 7 |
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----------------- -----------------
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-------------------------------------------------
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| BAM Data Multiplexer |
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-------------------------------------------------
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-----------------
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| BAM |
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-----------------
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Uplink data packets from a RMNET logical channel will have a mux packet
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header added to the top (identical to sdio_dmux), sent over BAM to the
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A2 module on the modem, where the packets will be de-muxed and processed.
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Downlink data packets will arive over BAM from A2, be de-muxed, have the
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mux header stripped and handed to RMNET via the logical channel indicated
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in the mux header.
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Logical channels will be established using the same handshake protocol
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used in sdio_dmux.
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Identical to sdio_dmux, a workqueue will be spawned during module
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initialization for the purpose of processing data from clients to prevent
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blocking, and to process data from BAM.
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Design
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======
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The goal of this design is to provide an interface to BAM for RMNET to
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achieve LTE data rates of 100 megabits per second. The sdio_dmux
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module already achieves this goal over SDIO, so its design was repurposed
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to achieve the same over the BAM transport.
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The basic use case for a logical channel would be
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1. for the client to register a platform driver on the logical channel.
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When the bam_dmux driver is ready, it will register platform
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devices for all the logical channels. This will cause the probe
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functions of all registered platform drivers to be invoked.
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2. Once invoked, the probe function can open a logical channel.
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3. After that, the client is free to queue data to be transmitted via the
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bam_dmux driver's write function.
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4. Received data will be sent to the client via the callback function
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registered at open().
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SMP/multi-core
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=============
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A number of data structures internal to the driver will store state, and
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will need to be protected against concurrent updates from multiple threads
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and interrupt handlers. Any structures that may be used in interrupt
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context will be protected with spinlocks, otherwise mutexes will suffice.
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Performance
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===========
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The expected data rate of traffic through bam_dmux is 100 megabits per
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second. The expected data rate per logical channel is 100/N megabits per
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second where N is the number of logical channels with active data at
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that point in time, depending on system load.
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Interface
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=========
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Bam_dmux will provide a simple API to kernel clients.
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Open:
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int msm_bam_dmux_open(uint32_t id, void *priv,
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void (*receive_cb)(void *, struct sk_buff *)
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void (*write_done)(void *, struct sk_buff *));
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id - id of the channel to open
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priv - private data pointer for the client, passed to the callbacks
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receive_cb - callback function. Invoked when data is read from BAM.
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Private data pointer and the data read are given as parameters.
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client must free sk_buff structure when done with the data.
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write_done - callback function. Invoked when data is successfully
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transmitted over BAM. Private data pointer and the data
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transmitted are given as parameters.
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return - 0 on success or negative value indicating error type
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Close:
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int msm_bam_dmux_close(uint32_t id);
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id - id of an open channel to close
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return - 0 on success or negative value indicating error type
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Write:
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int msm_bam_dmux_write(uint32_t id, struct sk_buff *skb);
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id - id of an open channel to queue data for transmit
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skb - data packet to transmit
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return - 0 on success or negative value indicating error type
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A debugfs node (bam_dmux) will be created with two subnodes within (tbl,
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loopback_test). The first node (tbl) will display diagnostic information
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such as the state of the logical channels and the amount of data
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read/transmitted. The second node (loopback_test) will provide a simple
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mechanism for putting the module into a loopback mode for functional testing.
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Dependencies
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============
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The bam_dmux requires the BAM driver. It will communicate with the
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A2 module on the modem through BAM for the purpose of transferring LTE rate
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data from RMNET to the modem.
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The bam_dmux driver depends on the socket buffer data structure which is
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provided as part of the standard linux kernel.
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