Brief history of Auxiliary Bus ============================== The auxiliary bus code was originally submitted upstream as virtual bus, and was submitted through the netdev tree. This process generated up to v4. This discussion can be found here: https://lore.kernel.org/netdev/20191111192219.30259-1-jeffrey.t.kirsher@inte...
At this point, GregKH requested that we take the review and revision process to an internal mailing list and garner the buy-in of a respected kernel contributor.
The auxiliary bus (then known as virtual bus) was originally submitted along with implementation code for the ice driver and irdma drive, causing the complication of also having dependencies in the rdma tree. This new submission is utilizing an auxiliary bus consumer in only the sound driver tree to create the initial implementation and a single user.
Since implementation work has started on this patch set, there have been multiple inquiries about the time frame of its completion. It appears that there will be numerous consumers of this functionality.
The process of internal review and implementation using the sound drivers generated 19 internal versions. The changes, including the name change from virtual bus to auxiliary bus, from these versions can be summarized as the following:
- Fixed compilation and checkpatch errors - Improved documentation to address the motivation for virtual bus. - Renamed virtual bus to auxiliary bus - increased maximum device name size - Correct order in Kconfig and Makefile - removed the mid-layer adev->release layer for device unregister - pushed adev->id management to parent driver - all error paths out of ancillary_device_register return error code - all error paths out of ancillary_device_register use put_device - added adev->name element - modname in register cannot be NULL - added KBUILD_MODNAME as prefix for match_name - push adev->id responsibility to registering driver - uevent now parses adev->dev name - match_id function now parses adev->dev name - changed drivers probe function to also take an ancillary_device_id param - split ancillary_device_register into device_initialize and device_add - adjusted what is done in device_initialize and device_add - change adev to ancildev and adrv to ancildrv - change adev to ancildev in documentation
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Introduces the auxiliary bus implementation along with the example usage in the Sound Open Firmware(SOF) audio driver.
In some subsystems, the functionality of the core device (PCI/ACPI/other) may be too complex for a single device to be managed as a monolithic block or a part of the functionality might need to be exposed to a different subsystem. Splitting the functionality into smaller orthogonal devices makes it easier to manage data, power management and domain-specific communication with the hardware. Also, common auxiliary_device functionality across primary devices can be handled by a common auxiliary_device. A key requirement for such a split is that there is no dependency on a physical bus, device, register accesses or regmap support. These individual devices split from the core cannot live on the platform bus as they are not physical devices that are controlled by DT/ACPI. The same argument applies for not using MFD in this scenario as it relies on individual function devices being physical devices that are DT enumerated.
An example for this kind of requirement is the audio subsystem where a single IP handles multiple entities such as HDMI, Soundwire, local devices such as mics/speakers etc. The split for the core's functionality can be arbitrary or be defined by the DSP firmware topology and include hooks for test/debug. This allows for the audio core device to be minimal and tightly coupled with handling the hardware-specific logic and communication.
The auxiliary bus is intended to be minimal, generic and avoid domain-specific assumptions. Each auxiliary bus device represents a part of its parent functionality. The generic behavior can be extended and specialized as needed by encapsulating an auxiliary bus device within other domain-specific structures and the use of .ops callbacks.
The SOF driver adopts the auxiliary bus for implementing the multi-client support. A client in the context of the SOF driver represents a part of the core device's functionality. It is not a physical device but rather an auxiliary device that needs to communicate with the DSP via IPCs. With multi-client support,the sound card can be separated into multiple orthogonal auxiliary devices for local devices (mic/speakers etc), HDMI, sensing, probes, debug etc. In this series, we demonstrate the usage of the auxiliary bus with the help of the IPC test client which is used for testing the serialization of IPCs when multiple clients talk to the DSP at the same time.
v4 changes: clean up passive voice clarify reg/unreg path for devices explicitly call out GPL v2
v3 changes: rename to auxiliary bus move .c file to drivers/base/ split auxdev unregister flow into uninitialize and delete steps update kernel-doc on register functions for new unregister model update documentation with new name and unregister flow remove check for release in auxiliary bus, allow core to catch Change driver register so only probe and id_table mandatory Fix matching logic in auxillary_match_id to account for longer id->name utilize auxiliary_bus callbacks for probe, remove and shutdown add auxiliary_find_device function add code to ensure unique auxdrv name shorten initialize/uninitialize in function names to init/uninit simplify looping logic in match_id in drives/base/Kconfig changed from tristate to bool Modified signature SOF client register/unregister API Modified PM runtime enabling sequence in the SOF ipc test aux driver Removed driver.name from the aux driver Added Probes client aux driver and device registration in the SOF driver. This allows for enabling the probes functionality in the SOF firmware for audio data extraction from specific points in the audio pipeline. Without auxiliary bus, the implementation requires modifying existing 15+ machine drivers to add the probes DAI links to the sounds cards. Using the auxiliary bus allows for splitting the probes implementation from the SOF core making it easy to maintain.
v2 changes: defined pr_fmt for kernel messages replaced WARN_ON calls in registration with pr_err calls adding kernel-doc function comments for device_initialize and device_add fix typo in documentation removed inaccurate line in documentation fixed formatting in drivers/bus/Makefile changed unwind path for sof_client_dev_alloc() improved comments for client list and mem freeing during client unreg removed debugfs entries in sof_ipc_test_client_drv during remove changed the signature of sof_debug_ipc_flood_test() fix a looping error in ancillary_match_id updated error value in sof_client_dev_register() mutex held while traversing client list when unregistering clients updated includes in sof-client.h
Dave Ertman (1): Add auxiliary bus support
Ranjani Sridharan (9): ASoC: SOF: Introduce descriptors for SOF client ASoC: SOF: Create client driver for IPC test ASoC: SOF: ops: Add ops for client registration ASoC: SOF: Intel: Define ops for client registration ASoC: SOF: Intel: Remove IPC flood test support in SOF core ASoC: SOF: sof-client: Add client APIs to access probes ops ASoC: SOF: compress: move and export sof_probe_compr_ops ASoC: SOF: Add new client driver for probes support ASoC: SOF: Intel: CNL: register probes client
Documentation/driver-api/auxiliary_bus.rst | 234 +++++++++++ Documentation/driver-api/index.rst | 1 + drivers/base/Kconfig | 3 + drivers/base/Makefile | 1 + drivers/base/auxiliary.c | 268 ++++++++++++ include/linux/auxiliary_bus.h | 78 ++++ include/linux/mod_devicetable.h | 8 + scripts/mod/devicetable-offsets.c | 3 + scripts/mod/file2alias.c | 8 + sound/soc/sof/Kconfig | 47 ++- sound/soc/sof/Makefile | 10 +- sound/soc/sof/compress.c | 60 +-- sound/soc/sof/compress.h | 1 + sound/soc/sof/core.c | 18 +- sound/soc/sof/debug.c | 457 --------------------- sound/soc/sof/intel/Kconfig | 9 + sound/soc/sof/intel/Makefile | 3 + sound/soc/sof/intel/apl.c | 16 + sound/soc/sof/intel/bdw.c | 16 + sound/soc/sof/intel/byt.c | 20 + sound/soc/sof/intel/cnl.c | 32 ++ sound/soc/sof/intel/hda-dai.c | 27 -- sound/soc/sof/intel/hda.h | 6 - sound/soc/sof/intel/intel-client.c | 40 ++ sound/soc/sof/intel/intel-client.h | 26 ++ sound/soc/sof/ops.h | 14 + sound/soc/sof/pcm.c | 11 - sound/soc/sof/probe.c | 124 +++--- sound/soc/sof/probe.h | 41 +- sound/soc/sof/sof-client.c | 170 ++++++++ sound/soc/sof/sof-client.h | 91 ++++ sound/soc/sof/sof-ipc-test-client.c | 321 +++++++++++++++ sound/soc/sof/sof-priv.h | 23 +- sound/soc/sof/sof-probes-client.c | 414 +++++++++++++++++++ 34 files changed, 1975 insertions(+), 626 deletions(-) create mode 100644 Documentation/driver-api/auxiliary_bus.rst create mode 100644 drivers/base/auxiliary.c create mode 100644 include/linux/auxiliary_bus.h create mode 100644 sound/soc/sof/intel/intel-client.c create mode 100644 sound/soc/sof/intel/intel-client.h create mode 100644 sound/soc/sof/sof-client.c create mode 100644 sound/soc/sof/sof-client.h create mode 100644 sound/soc/sof/sof-ipc-test-client.c create mode 100644 sound/soc/sof/sof-probes-client.c