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