Re: [PATCH] xhci: sideband: check vdev liveness before removing endpoints on unregister

[Michal Pecio <michal.pecio@gmail.com>]

On Tue, 15 Sep 2026 08:35:40 +0000, 胡连勤 wrote:
> The snd-usb-audio driver sets supports_autosuspend = 1
> (card.c:1347), so the device can autosuspend when no audio stream
> is active.
> 
> During suspend, usb_audio_suspend() calls
> platform_ops->suspend_cb → qc_usb_audio_offload_suspend(),
> which sends a QMI disconnect indication to the ADSP and waits for
> dev->in_use to be cleared.
> 
> However, qc_usb_audio_offload_suspend() does not call
> xhci_sideband_remove_endpoint() or xhci_sideband_unregister().
> The sideband registration stays active during suspend — the
> endpoint pointers to xHCI ring buffers remain in place.
> 
> This is the root design issue: the sideband client assumes the
> xHCI ring buffers remain valid across suspend/resume cycles. But
> on reset-resume, usb_reset_and_verify_device() → hub_port_init()
> → xhci_discover_or_reset_device() frees and reallocates those
> rings, invalidating the sideband's pointers.
> 
> Your suggestion is correct — the proper fix is for the audio
> offload driver to remove sideband endpoints during suspend and
> re-add them during resume, rather than leaving them registered
> across suspend/resume cycles.

What's the state of the audio streaming interface during supend?
Is it being switched to altsetting 0, with side effect of removing
the isoc endpoint and then re-adding it after resume?

If yes, that seems like a problem already, because the ring may be
reallocated to a different address. Is this handled?

If not, then disabling sideband without disabling the endpoint may
conflict with pending "large page support" patches, which (IIRC)
assume that sideband is added *before* enabling the endpoint. So
either we solve this without disabling sideband on suspend or there
must be rule that sideband can be added/removed at any time.

Regards,
Michal