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Sat, 29 Aug 2026 03:03:40 -0700 (PDT) From: =?UTF-8?q?Isma=C3=AFl=20Bahloul?= To: linux-sound@vger.kernel.org Cc: linux-usb@vger.kernel.org, alsa-devel@alsa-project.org, perex@perex.cz, tiwai@suse.com, linux-kernel@vger.kernel.org, =?UTF-8?q?Isma=C3=AFl=20Bahloul?= Subject: [RFC PATCH 0/1] RME Babyface Pro FS driver (proprietary mode) Date: Sat, 29 Aug 2026 11:03:32 +0100 Message-ID: <20260829100333.32933-1-i.bahloul01@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi, I'm sending this as an RFC for a driver I've been working on for the RME Babyface Pro FS in its proprietary USB mode (VID 0x2a39, PID 0x3fc0). In that mode the PCM stream runs on interrupt endpoints (interface 5, ep 0x01 OUT / 0x82 IN) instead of the class-compliant isochronous path, so it can't be handled as a quirk on top of snd-usb-audio. It needs a standalone driver, and I modeled it on snd-usb-caiaq, which is the existing in-tree precedent for interrupt-based USB audio streaming. The driver is hardware-validated on a real unit and the code is checkpatch, sparse and W=1 clean. The vendor protocol (control requests, register map, front-panel readback) was reverse-engineered from Windows USB captures and verified bit by bit on hardware. The capture analysis, the calibrated laws, and a userspace reference implementation live in the sibling TuxMix repo (https://github.com/ismail-bahloul/TuxMix). This driver is the kernel side of that effort. What's included: - Interrupt-URB PCM streaming, full-duplex, 2-12 channels, S24_LE, 9 sample rates from 32 to 192 kHz across 3 USB bandwidth classes. - ALSA mixer: 6 output masters and mutes, the 6x14 crosspoint routing matrix, 4 mic/instrument preamp gains with phantom power and PAD, pitch/varispeed, loopback, and a few device-specific toggles (AN 1>2, input link, MS processor, DIM, width, FX send). - Front-panel emulation. The unit has no onboard DSP for its own panel, so the host mirrors TotalMix's role: it translates physical wheel/button events into mixer writes and exposes the decoded panel state as read-only ALSA controls. - A hardware 3-band plus low-cut parametric EQ for the 4 analog-input strips, computed in fixed-point (no FPU use) and uploaded as coefficient blocks. - Mixer-state persistence across interface re-probes and system suspend/resume, because the firmware has no state readback of its own. Validation: a full-duplex sweep across the whole rate x period matrix with a signal-integrity tap, start/stop stress (30 cycles), mixer-state restore across an interface unbind/rebind, and a mid-stream disconnect. All of that runs through the automated regression suite kept in the driver's development tree. Known limitations, stated up front: - USB autosuspend is not supported yet. I disable it explicitly (usb_disable_autosuspend at probe, balanced at disconnect) rather than ship something untested. The front-panel poll and keepalive work items run continuously, and nothing pairs usb_autopm_get/put around the stream, so an autosuspend request could race a live stream. S3 suspend/resume works and is tested. Full autosuspend (pausing the panel/keepalive work plus autopm pairing) is a follow-up. - A few protocol items aren't fully pinned down, but they don't affect the shipped controls; the relevant paths are hardware-verified. They are documented as open in PROTOCOL.md: the preamp readback index semantics (0x003F vs 0x0000), a width strip-ownership edge case, and the exact high-frequency warping of the EQ coefficient computation versus TotalMix's curve. - The latency profile is selected at load time via the frames_per_urb and nurbs module params. Default is 256 frames/URB, matching TotalMix's 256-sample buffer; frames_per_urb=16 nurbs=16 gives a 0.33 ms monitoring-grade floor. Changing profile currently means a module reload. A runtime reconfiguration (like RME's own Fireface USB Settings panel) is a post-merge follow-up. This is an RFC. I'm mainly after feedback on the interrupt-URB PCM design, the control naming and topology, the two-file split, and whether a subdirectory (sound/usb/babyfacepro/) is the right layout. I sent it as a single patch (4651 lines, 7 files) because that's how a wholesale new-driver addition is usually submitted, but I can split it into a series if that's preferred. Thanks for reading, Ismaïl Ismaïl Bahloul (1): ALSA: usb: add RME Babyface Pro FS driver (proprietary mode) MAINTAINERS | 6 + sound/usb/Kconfig | 18 + sound/usb/Makefile | 2 +- sound/usb/babyfacepro/Makefile | 2 + sound/usb/babyfacepro/babyfacepro-ctl.c | 2782 +++++++++++++++++++++++ sound/usb/babyfacepro/babyfacepro.c | 1449 ++++++++++++ sound/usb/babyfacepro/babyfacepro.h | 391 ++++ 7 files changed, 4649 insertions(+), 1 deletion(-) create mode 100644 sound/usb/babyfacepro/Makefile create mode 100644 sound/usb/babyfacepro/babyfacepro-ctl.c create mode 100644 sound/usb/babyfacepro/babyfacepro.c create mode 100644 sound/usb/babyfacepro/babyfacepro.h -- 2.55.0