Hi Sergey, On Tue, Jul 20, 2021 at 12:10:42PM +0300, Sergey Ryazanov wrote: > On Mon, Jul 19, 2021 at 6:01 PM Stephan Gerhold <stephan@xxxxxxxxxxx> wrote: > > 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. > > > > 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...] | | | | > > ---------->|rmnet0 | [DMUX chan: x] | | > > [IPv4/6] | (chan: 0) | [IPv4/6] | | > > [Data...] | | [Data...] | | > > ---------->|rmnet1 |--------------->| Modem | > > | (chan: 1) | BAM | | > > [IPv4/6] | ... | (DMA Engine) | | > > [Data...] | | | | > > ---------->|rmnet7 | | | > > | (chan: 7) | | | > > +------------+ +-------+ > > > > However, on newer SoCs/firmware versions Qualcomm began gradually moving > > to QMAP (rmnet driver) as backend-independent protocol for multiplexing > > and data aggegration. Some firmware versions allow using QMAP on top of > > BAM-DMUX (effectively resulting in a second multiplexing layer plus data > > aggregation). The architecture with QMAP would look roughly like this: > > > > +-------------+ +------------+ +-------+ > > [IPv4/6] | RMNET | | BAM-DMUX | | | > > [Data...] | | | | [DMUX chan: 0] | | > > ---------->|rmnet_data1 | ----->|rmnet0 | [QMAP mux-id: x] | | > > | (mux-id: 1) | | | (chan: 0) | [IPv4/6] | | > > | | | | | [Data...] | | > > [IPv4/6] | ... |------ | |----------------->| Modem | > > [Data...] | | | | BAM | | > > ---------->|rmnet_data42 | [QMAP: x] |[rmnet1] | (DMA Engine) | | > > | (mux-id: 42)| [IPv4/6] |... unused! | | | > > | | [Data...] |[rmnet7] | | | > > | | | | | | > > +-------------+ +------------+ +-------+ > > > > In this case, rmnet1-7 would remain unused. The firmware used on the most > > recent SoCs with BAM-DMUX even seems to announce only a single BAM-DMUX > > channel (rmnet0), which makes QMAP the only option for multiplexing there. > > > > So far the driver is mainly tested on various smartphones/tablets based on > > Qualcomm MSM8916/MSM8974 without QMAP. It looks like QMAP depends on a MTU > > negotiation feature in BAM-DMUX which is not yet supported by the driver. > > > > Signed-off-by: Stephan Gerhold <stephan@xxxxxxxxxxx> > > --- > > Note that this is my first network driver, so I apologize in advance > > if I made some obvious mistakes. :) > > > > I'm not sure how to integrate the driver with the WWAN subsystem yet. > > At the moment the driver creates network interfaces for all channels > > announced by the modem, it does not make use of the WWAN link management > > yet. Unfortunately, this is a bit complicated: > > > > Both QMAP and the built-in multiplexing layer might be needed at some point. > > There are firmware versions that do not support QMAP and the other way around > > (the built-in multiplexing was disabled on very recent firmware versions). > > Only userspace can check if QMAP is supported in the firmware (via QMI). > > I am not very familiar with the Qualcomm protocols and am just curious > whether BAM-DMUX has any control (management) channels or only IPv4/v6 > data channels? > > The WWAN subsystem began as a framework for exporting management > interfaces (MBIM, AT, etc.) to user space. And then the network > interfaces (data channels) management interface was added to > facilitate management of devices with multiple data channels. That is > why I am curious about the BAM-DMUX device management interface or in > other words, how a user space application could control the modem > work? > Sorry for the confusion! It's briefly mentioned in the Kconfig option but I should have made this more clear in the commit message. It was so long already that I wasn't sure where to put it. :) BAM-DMUX does not have any control channels. Instead I use it together with the rpmsg_wwan_ctrl driver [1] that I already submitted for 5.14. The control/data channels are pretty much separate in this setup and don't have much to do with each other. I also had a short overview of some of the many different modem protocols Qualcomm has come up with in a related RFC for that driver, see [2] if you are curious. I hope that clarifies some things, please let me know if I should explain something better! :) Thanks! Stephan [1]: https://lore.kernel.org/netdev/20210618173611.134685-3-stephan@xxxxxxxxxxx/ [2]: https://lore.kernel.org/netdev/YLfL9Q+4860uqS8f@xxxxxxxxxxx/
