Re: [PATCH v4 0/2] usb: offload: Decouple interrupter lifecycle and refactor usage tracking

[Greg KH <gregkh@linuxfoundation.org>]

On Wed, Apr 01, 2026 at 12:32:16PM +0000, Guan-Yu Lin wrote:
> The current USB offload implementation couples the allocation of xHCI
> sideband interrupters with the device's offload usage counter. This
> coupling is conceptually incorrect, as hardware resource availability
> and power management state serve distinct purposes.
> 
> Furthermore, the reliance on the coarse USB device lock for offload
> state updates has led to potential recursive locking issues,
> especially during device disconnect when the lock is already held
> by the USB core.
> 
> This series refactors the offload synchronization by introducing a
> dedicated spinlock for offload state, allowing for more granular
> concurrency control and avoiding deadlocks. It also optimizes power
> management by ensuring that offload state is only modified when the
> device is already active, avoiding unnecessary auto-resumes.
> 
> Patch 1 introduces the `offload_lock` spinlock and `offload_pm_locked`
> synchronization, replacing the coarse `udev->lock` and the legacy
> `offload_at_suspend` flag. It also updates `usb_offload_get/put` to use
> `pm_runtime_get_if_active()`.
> 
> Patch 2 removes the implicit usage tracking from the xHCI sideband layer
> and delegates the responsibility to class drivers, who have the
> correct context for managing offload data stream activity.

Ok, this looks much better, thanks for the revisions.

If the xhci maintainer acks these, I'll be glad to apply them to my
tree.

thanks,

greg k-h