Re: [PATCH] ALSA: usb-audio: Complete cleanup after system-resume errors

On Tue, 25 Aug 2026 00:57:57 +0200,
Will Porter wrote:
> 
> A failed system resume can leave the card unusable until reboot.
> usb_audio_resume() jumps to err_out when snd_usb_pcm_resume() or
> snd_usb_mixer_resume() fails. The error path skips the out: block, which
> restores D0 and decrements chip->num_suspended_intf.
> 
> The card stays in SNDRV_CTL_POWER_D3hot, so later control access blocks in
> snd_power_ref_and_wait(). USB core logs an interface resume callback error.
> It does not retry that callback, so a later callback cannot complete the
> skipped cleanup.
> 
> usb_audio_suspend() increments num_suspended_intf before returning success.
> A system-resume callback must consume the system-suspend count even if a
> component resume fails. Otherwise, the stranded count skews later suspend
> and resume cycles.
> 
> Do not apply this cleanup to runtime-resume errors. Runtime PM can retry
> -EAGAIN or -EBUSY without another suspend callback. The count must continue
> to describe that suspended interface. Other runtime-resume errors latch
> runtime_error in the PM core and do not cause an immediate callback retry.
> 
> Both parts of the system-resume error path are longstanding. Commit
> 88a8516a2128a ("ALSA: usbaudio: implement USB autosuspend") introduced
> err_out past the D0 restore. Commit 862b2509d157c ("ALSA: usb-audio: Fix
> inconsistent card PM state after resume") later moved
> num_suspended_intf-- into the out: block. The error path now skips both
> operations.
> 
> No third-party code is needed to reach the error path.
> snd_usb_mixer_resume() ends in snd_usb_mixer_activate(), which returns the
> result of usb_submit_urb() for devices that have a mixer status URB. Its
> mixer->private_resume hook can also fail through scarlett2_init_notify().
> snd_usb_pcm_resume() issues a SET_CUR request to a UAC3 power domain. It
> can return -EPIPE or -EIO when the device stalls the request.
> 
> Route a component error through out: only when system_suspend is nonzero.
> Continue to return runtime-resume errors through err_out. Later component
> resume stages remain skipped. The original error still reaches USB core.
> A later transfer can fail if the device did not recover.
> 
> I reproduced the system-resume failure on an Audient iD14 MkI with an
> out-of-tree diagnostic mixer resume hook. An injected -EIO on the unpatched
> core left control readers in uninterruptible sleep in
> snd_power_ref_and_wait() until a reboot. With this patch, the same failure
> restored control access. A second system suspend and resume also succeeded
> after I disabled fault injection.
> 
> Assisted-by: Claude:claude-opus-5
> Assisted-by: Antigravity:gemini-3.1-pro-high
> Assisted-by: Codex:gpt-5.6-sol
> Fixes: 88a8516a2128a ("ALSA: usbaudio: implement USB autosuspend")
> Fixes: 862b2509d157c ("ALSA: usb-audio: Fix inconsistent card PM state after resume")
> Cc: <[email protected]>
> Signed-off-by: Will Porter <[email protected]>

Applied now.  Thanks.


Takashi