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786f91da85
set_sample_rate_v2v3() returns early when the clock already reports the
requested rate:
prev_rate = get_sample_rate_v2v3(chip, fmt->iface,
fmt->altsetting, clock);
if (prev_rate == rate)
goto validation;
A device advertising exactly one sample rate always takes this branch, so
it never receives a SET_CUR for CS_SAM_FREQ_CONTROL at all.
The Mackie DLZ Creator XS (0a73:003a, 14 in / 4 out, 48 kHz only) requires
that write. Without it the device drops off the USB bus roughly 0.2-1.8 s
into any stream, clearing its port CONNECTION bit; captured audio is
byte-correct until the instant it vanishes.
USBPcap traces of a cold-booted device on Windows show SET_CUR 48000 issued
unconditionally on every stream start, followed by clean streaming. The
device is otherwise driven with plain class-compliant UAC2 - it also works
on iOS, which cannot load a vendor driver - so no vendor-specific
initialization is involved.
The device is self-powered, so the resulting state survives a USB replug:
initializing it on any host that issues the write leaves it working on
Linux until it is power-cycled, which made the failure look intermittent.
Add a quirk flag rather than dropping the early exit, since the opposite
requirement also exists in-tree: QUIRK_FLAG_FIXED_RATE suppresses rate
setting for single-rate devices (JBL Quantum610/810). The two behaviors
are device-dependent and cannot both be the default.
A/B on identically cold-booted hardware, same kernel, same port, repeated
twice:
without the flag device dropped after 5-6 s, then again after 3-4 s
with the flag 20 s playback followed by 20 s of 14-channel capture,
960000 frames, zero re-enumerations
This change was developed with an AI coding assistant. The assistant did
the trace analysis that located the bug and wrote the patch and this
changelog; the hardware testing, the cold-boot cycles and the decision to
submit were the author's. Several earlier hypotheses it proposed - URB
queue depth, isochronous packet under-allocation, endpoint start ordering -
were disproven by measurement before this one.
The bug was located with usbmon on Linux and USBPcap on Windows, by
diffing an enumeration capture of a cold-booted device on each host.
Verified on physical hardware by the A/B above.
Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: JJ Macalinao <jj@macalinao.org>
Link: https://patch.msgid.link/20260808172726.1107550-1-jj@macalinao.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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| ipc | ||
| kernel | ||
| lib | ||
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| .clang-format | ||
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| .cocciconfig | ||
| .editorconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| .pylintrc | ||
| .rustfmt.toml | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
Linux kernel ============ The Linux kernel is the core of any Linux operating system. It manages hardware, system resources, and provides the fundamental services for all other software. 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