[PATCH v3 0/1] ALSA: usb: Add support for Reloop Jockey 3 DJ controllers

[Frank van de Pol <fvdpol@gmail.com>]

Hi Takashi, Jaroslav, and the ALSA community,

After being away from active ALSA development for some 25 years or so, I am
happy to submit this patch to introduce a dedicated driver supporting the
Jockey 3 series of DJ Controllers made by Reloop (specifically covering the
Master Edition and the Remix variants).

I initially evaluated the feasibility of integrating the required logic to
handle the non-standard proprietary Ploytec framing protocol into the standard
USB-audio driver via quirks. However, doing so would require introducing
numerous hardware-specific exceptions throughout the core layout, adding
significant complexity. A clean, isolated driver subdirectory provides much
better long-term maintainability without cluttering the existing class-compliant
architecture.

Following up on the feedback received from the v1 and v2 submissions of my
driver, I have made several updates to the code to improve locking consistency,
lifecycle safety, and the general readability and maintainability of the code.

Changes v1 -> v2:
 - Migrated URB lifecycle management to use standard usb_anchors.
 - Revised and hardened URB buffer memory allocation constraints.
 - Addressed locking consistency, scoping issues, and static analysis warnings
   raised by Takashi and the Sashiko automated review.
 - Implemented dynamic PCM rate constraints when a stream is active.
 - Implemented full MIDI Running Status support for the control surface.
 - Refactored several large code blocks to improve overall readability.
 - Added clarifications on hardware-specific quirks and codec format.
 - Optimized struct jockey3_chip layout for padding and locality.

Changes v2 -> v3:
 - Removed redundant dependencies and defaults from Kconfig.
 - Fixed an AB-BA deadlock condition highlighted by Sashiko review.
 - Corrected an URB resubmission race condition.
 - Implemented explicit USB endpoint validation during initialization.
 - Added Sample Rate verification and post-reset recovery handling.
 - Abstracted disconnect and stopping status checks out into helper functions.
 - Moved substream registration safely under the chip spinlock.
 - Implemented native suspend/resume power management triggers and callbacks.
 - Refactored jockey3_probe() and jockey3_pcm_trigger() for cleaner state tracking.
 - Further refined the internal MIDI Running Status state parser logic.

I have successfully validated and stress-tested this driver across three
distinct hardware architectures to ensure robustness regarding DMA, timing,
and memory alignment:

 - x86_64 (Standard PC desktop environment)
 - armhf (32-bit on a Raspberry Pi 1B -- functional, though tight at 96 kHz)
 - arm64 (64-bit modern SoC environment on a Raspberry Pi 4)

I look forward to your review and feedback, and I am more than happy to
make further architectural adjustments as required.

Best regards,
Frank

Frank van de Pol (1):
  ALSA: usb: Add support for Reloop Jockey 3 DJ controllers

 MAINTAINERS                       |    7 +
 sound/usb/Kconfig                 |    1 +
 sound/usb/Makefile                |    1 +
 sound/usb/jockey3/Kconfig         |   17 +
 sound/usb/jockey3/Makefile        |    3 +
 sound/usb/jockey3/jockey3.c       | 1188 +++++++++++++++++++++++++++++
 sound/usb/jockey3/ploytec_proto.c |  330 ++++++++
 sound/usb/jockey3/ploytec_proto.h |   66 ++
 8 files changed, 1613 insertions(+)
 create mode 100644 sound/usb/jockey3/Kconfig
 create mode 100644 sound/usb/jockey3/Makefile
 create mode 100644 sound/usb/jockey3/jockey3.c
 create mode 100644 sound/usb/jockey3/ploytec_proto.c
 create mode 100644 sound/usb/jockey3/ploytec_proto.h

-- 
2.47.3