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The BAM Data Multiplexer provides access to the network data channels of
modems integrated into many older Qualcomm SoCs, e.g. Qualcomm MSM8916 or
MSM8974. It is built using a simple protocol layer on top of a DMA engine
(Qualcomm BAM) and bidirectional interrupts to coordinate power control.
The modem announces a fixed set of channels by sending an OPEN command.
The driver exports each channel as separate network interface so that
a connection can be established via QMI from userspace. The network
interface can work either in Ethernet or Raw-IP mode (configurable via
QMI). However, Ethernet mode seems to be broken with most firmwares
(network packets are actually received as Raw-IP), therefore the driver
only supports Raw-IP mode.
Note that the control channel (QMI/AT) is entirely separate from
BAM-DMUX and is already supported by the RPMSG_WWAN_CTRL driver.
The driver uses runtime PM to coordinate power control with the modem.
TX/RX buffers are put in a kind of "ring queue" and submitted via
the bam_dma driver of the DMAEngine subsystem.
The basic architecture looks roughly like this:
+------------+ +-------+
[IPv4/6] | BAM-DMUX | | |
[Data...] | | | |
---------->|wwan0 | [DMUX chan: x] | |
[IPv4/6] | (chan: 0) | [IPv4/6] | |
[Data...] | | [Data...] | |
---------->|wwan1 |--------------->| Modem |
| (chan: 1) | BAM | |
[IPv4/6] | ... | (DMA Engine) | |
[Data...] | | | |
---------->|wwan7 | | |
| (chan: 7) | | |
+------------+ +-------+
Note that some newer firmware versions support QMAP ("rmnet" driver)
as additional multiplexing layer on top of BAM-DMUX, but this is not
currently supported by this driver.
Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
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