[RFC PATCH net-next 0/4] net: wwan: Add Qualcomm BAM-DMUX WWAN network driver

[Stephan Gerhold <stephan@gerhold.net>]

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. This series adds a driver that allows using it.

For more information about BAM-DMUX, see PATCH 4/4.

Shortly said, BAM-DMUX is built using a simple protocol layer on top of
a DMA engine (Qualcomm BAM DMA). For BAM-DMUX, the BAM DMA engine runs in
a quite strange mode that I call "remote power collapse", where the
modem/remote side is responsible for powering on the BAM when needed but we
are responsible to initialize it. The BAM is power-collapsed when unneeded
by coordinating power control via bidirectional interrupts from the
BAM-DMUX driver.

The series first adds one possible solution for handling this "remote power
collapse" mode in the bam_dma driver, then it adds the BAM-DMUX driver to
the WWAN subsystem. Note that the BAM-DMUX driver does not actually make
use of the WWAN subsystem yet, since I'm not sure how to fit it in there
yet (see PATCH 4/4).

Please note that all of the changes in this patch series are based on
a fairly complicated driver from Qualcomm [1].
I do not have access to any documentation about "BAM-DMUX". :(

The driver has been used in postmarketOS [2] on various smartphones/tablets
based on Qualcomm MSM8916 and MSM8974 for a year now with no reported
problems.

At runtime (but not compile-time), the following two patches are needed
additionally for full functionality:
  - https://lore.kernel.org/linux-arm-msm/20210712135703.324748-1-stephan@gerhold.net/
  - https://lore.kernel.org/linux-arm-msm/20210712135703.324748-2-stephan@gerhold.net/

[1]: https://source.codeaurora.org/quic/la/kernel/msm-3.10/tree/drivers/soc/qcom/bam_dmux.c?h=LA.BR.1.2.9.1-02310-8x16.0
[2]: https://postmarketos.org/

Stephan Gerhold (4):
  dt-bindings: dmaengine: bam_dma: Add remote power collapse mode
  dmaengine: qcom: bam_dma: Add remote power collapse mode
  dt-bindings: net: Add schema for Qualcomm BAM-DMUX
  net: wwan: Add Qualcomm BAM-DMUX WWAN network driver

 .../devicetree/bindings/dma/qcom_bam_dma.txt  |   2 +
 .../bindings/net/qcom,bam-dmux.yaml           |  87 ++
 MAINTAINERS                                   |   8 +
 drivers/dma/qcom/bam_dma.c                    |  88 +-
 drivers/net/wwan/Kconfig                      |  13 +
 drivers/net/wwan/Makefile                     |   1 +
 drivers/net/wwan/qcom_bam_dmux.c              | 907 ++++++++++++++++++
 7 files changed, 1074 insertions(+), 32 deletions(-)
 create mode 100644 Documentation/devicetree/bindings/net/qcom,bam-dmux.yaml
 create mode 100644 drivers/net/wwan/qcom_bam_dmux.c

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2.32.0