[RFC PATCH v2 0/2] usb: offload: Decouple interrupter lifecycle and refactor usage tracking

[RFC PATCH v2 0/2] usb: offload: Decouple interrupter lifecycle and refactor usage tracking

[Guan-Yu Lin]

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.

This series decouples these mechanisms by removing the usage counting
logic from the xHCI sideband layer and shifting the responsibility
to the consumer drivers. This allows interrupters to be managed
independently of the device's active offload status.

Furthermore, this refactoring addresses a recursive locking issue.
When a USB device is disconnected, the USB core invokes the driver's
disconnect callback while holding the udev device lock. Previously,
the xHCI sideband layer would call usb_offload_put(), which
attempted to re-acquire the same udev lock, resulting in a deadlock.

By shifting lock acquisition responsibility to the upper-level USB
driver, we ensure that offload usage updates can be safely performed
from contexts where the lock is already held. This standardizes the
lock hierarchy and prevents potential deadlocks during teardown.

Patch 1 performs the core refactoring by updating the offload APIs
to require caller-held device locks and removing implicit usage
counting from the interrupter paths.

Patch 2 updates the Qualcomm USB audio offload driver to explicitly
manage the usage counter during its stream lifecycle, serving as a
derivative consumer of the new API contract. This also ensures the
device remains active during playback, preventing premature
autosuspend.

---
Changes in v2:
- Move device locking to callers 
- Decouple sideband from offload counting.
Link to v1: https://lore.kernel.org/all/20260130074746.287750-1-guanyulin@google.com/
---
Guan-Yu Lin (2):
  usb: offload: move device locking to callers in offload.c
  ALSA: usb: qcom: manage offload device usage

 drivers/usb/core/offload.c        | 34 +++++++++++--------------------
 drivers/usb/host/xhci-sideband.c  | 14 +------------
 sound/usb/qcom/qc_audio_offload.c | 23 ++++++++++++++++++---
 3 files changed, 33 insertions(+), 38 deletions(-)

-- 
2.53.0.273.g2a3d683680-goog

[RFC PATCH v2 1/2] usb: offload: move device locking to callers in offload.c

[Guan-Yu Lin]

Update usb_offload_get() and usb_offload_put() to require that the
caller holds the USB device lock. Remove the internal call to
usb_lock_device() and add device_lock_assert() to ensure synchronization
is handled by the caller. These functions continue to manage the
device's power state via autoresume/autosuspend and update the
offload_usage counter.

Additionally, decouple the xHCI sideband interrupter lifecycle from the
offload usage counter by removing the calls to usb_offload_get() and
usb_offload_put() from the interrupter creation and removal paths. This
allows interrupters to be managed independently of the device's offload
activity status.

Cc: stable@vger.kernel.org
Fixes: ef82a4803aab ("xhci: sideband: add api to trace sideband usage")
Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 drivers/usb/core/offload.c       | 34 +++++++++++---------------------
 drivers/usb/host/xhci-sideband.c | 14 +------------
 2 files changed, 13 insertions(+), 35 deletions(-)

diff --git a/drivers/usb/core/offload.c b/drivers/usb/core/offload.c
index 7c699f1b8d2b..e13a4c21d61b 100644
--- a/drivers/usb/core/offload.c
+++ b/drivers/usb/core/offload.c
@@ -20,6 +20,7 @@
  * enabled on this usb_device; that is, another entity is actively handling USB
  * transfers. This information allows the USB driver to adjust its power
  * management policy based on offload activity.
+ * The caller must hold @udev's device lock.
  *
  * Return: 0 on success. A negative error code otherwise.
  */
@@ -27,31 +28,25 @@ int usb_offload_get(struct usb_device *udev)
 {
 	int ret;
 
-	usb_lock_device(udev);
-	if (udev->state == USB_STATE_NOTATTACHED) {
-		usb_unlock_device(udev);
+	device_lock_assert(&udev->dev);
+
+	if (udev->state == USB_STATE_NOTATTACHED)
 		return -ENODEV;
-	}
 
 	if (udev->state == USB_STATE_SUSPENDED ||
-		   udev->offload_at_suspend) {
-		usb_unlock_device(udev);
+	    udev->offload_at_suspend)
 		return -EBUSY;
-	}
 
 	/*
 	 * offload_usage could only be modified when the device is active, since
 	 * it will alter the suspend flow of the device.
 	 */
 	ret = usb_autoresume_device(udev);
-	if (ret < 0) {
-		usb_unlock_device(udev);
+	if (ret < 0)
 		return ret;
-	}
 
 	udev->offload_usage++;
 	usb_autosuspend_device(udev);
-	usb_unlock_device(udev);
 
 	return ret;
 }
@@ -64,6 +59,7 @@ EXPORT_SYMBOL_GPL(usb_offload_get);
  * The inverse operation of usb_offload_get, which drops the offload_usage of
  * a USB device. This information allows the USB driver to adjust its power
  * management policy based on offload activity.
+ * The caller must hold @udev's device lock.
  *
  * Return: 0 on success. A negative error code otherwise.
  */
@@ -71,33 +67,27 @@ int usb_offload_put(struct usb_device *udev)
 {
 	int ret;
 
-	usb_lock_device(udev);
-	if (udev->state == USB_STATE_NOTATTACHED) {
-		usb_unlock_device(udev);
+	device_lock_assert(&udev->dev);
+
+	if (udev->state == USB_STATE_NOTATTACHED)
 		return -ENODEV;
-	}
 
 	if (udev->state == USB_STATE_SUSPENDED ||
-		   udev->offload_at_suspend) {
-		usb_unlock_device(udev);
+	    udev->offload_at_suspend)
 		return -EBUSY;
-	}
 
 	/*
 	 * offload_usage could only be modified when the device is active, since
 	 * it will alter the suspend flow of the device.
 	 */
 	ret = usb_autoresume_device(udev);
-	if (ret < 0) {
-		usb_unlock_device(udev);
+	if (ret < 0)
 		return ret;
-	}
 
 	/* Drop the count when it wasn't 0, ignore the operation otherwise. */
 	if (udev->offload_usage)
 		udev->offload_usage--;
 	usb_autosuspend_device(udev);
-	usb_unlock_device(udev);
 
 	return ret;
 }
diff --git a/drivers/usb/host/xhci-sideband.c b/drivers/usb/host/xhci-sideband.c
index 2bd77255032b..6fc0ad658d66 100644
--- a/drivers/usb/host/xhci-sideband.c
+++ b/drivers/usb/host/xhci-sideband.c
@@ -93,8 +93,6 @@ __xhci_sideband_remove_endpoint(struct xhci_sideband *sb, struct xhci_virt_ep *e
 static void
 __xhci_sideband_remove_interrupter(struct xhci_sideband *sb)
 {
-	struct usb_device *udev;
-
 	lockdep_assert_held(&sb->mutex);
 
 	if (!sb->ir)
@@ -102,10 +100,6 @@ __xhci_sideband_remove_interrupter(struct xhci_sideband *sb)
 
 	xhci_remove_secondary_interrupter(xhci_to_hcd(sb->xhci), sb->ir);
 	sb->ir = NULL;
-	udev = sb->vdev->udev;
-
-	if (udev->state != USB_STATE_NOTATTACHED)
-		usb_offload_put(udev);
 }
 
 /* sideband api functions */
@@ -328,9 +322,6 @@ int
 xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
 				 bool ip_autoclear, u32 imod_interval, int intr_num)
 {
-	int ret = 0;
-	struct usb_device *udev;
-
 	if (!sb || !sb->xhci)
 		return -ENODEV;
 
@@ -348,12 +339,9 @@ xhci_sideband_create_interrupter(struct xhci_sideband *sb, int num_seg,
 	if (!sb->ir)
 		return -ENOMEM;
 
-	udev = sb->vdev->udev;
-	ret = usb_offload_get(udev);
-
 	sb->ir->ip_autoclear = ip_autoclear;
 
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(xhci_sideband_create_interrupter);
 
-- 
2.53.0.273.g2a3d683680-goog

[RFC PATCH v2 2/2] ALSA: usb: qcom: manage offload device usage

[Guan-Yu Lin]

The Qualcomm USB audio offload driver currently does not report its offload
activity to the USB core. This prevents the USB core from properly tracking
active offload sessions, which could allow the device to auto-suspend while
audio offloading is in progress.

Integrate usb_offload_get() and usb_offload_put() calls into the offload
stream setup and teardown paths. Specifically, call usb_offload_get() when
initializing the event ring and usb_offload_put() when freeing it.

Since the updated usb_offload_get() and usb_offload_put() APIs require the
caller to hold the USB device lock, add the necessary device locking in
handle_uaudio_stream_req() and qmi_stop_session() to satisfy this
requirement.

Cc: stable@vger.kernel.org
Fixes: ef82a4803aab ("xhci: sideband: add api to trace sideband usage")
Signed-off-by: Guan-Yu Lin <guanyulin@google.com>
---
 sound/usb/qcom/qc_audio_offload.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/sound/usb/qcom/qc_audio_offload.c b/sound/usb/qcom/qc_audio_offload.c
index cfb30a195364..6bcb6033e688 100644
--- a/sound/usb/qcom/qc_audio_offload.c
+++ b/sound/usb/qcom/qc_audio_offload.c
@@ -699,6 +699,7 @@ static void uaudio_event_ring_cleanup_free(struct uaudio_dev *dev)
 		uaudio_iommu_unmap(MEM_EVENT_RING, IOVA_BASE, PAGE_SIZE,
 				   PAGE_SIZE);
 		xhci_sideband_remove_interrupter(uadev[dev->chip->card->number].sb);
+		usb_offload_put(dev->udev);
 	}
 }
 
@@ -750,6 +751,7 @@ static void qmi_stop_session(void)
 	struct snd_usb_substream *subs;
 	struct usb_host_endpoint *ep;
 	struct snd_usb_audio *chip;
+	struct usb_device *udev;
 	struct intf_info *info;
 	int pcm_card_num;
 	int if_idx;
@@ -791,8 +793,13 @@ static void qmi_stop_session(void)
 			disable_audio_stream(subs);
 		}
 		atomic_set(&uadev[idx].in_use, 0);
-		guard(mutex)(&chip->mutex);
-		uaudio_dev_cleanup(&uadev[idx]);
+
+		udev = uadev[idx].udev;
+		if (udev) {
+			guard(device)(&udev->dev);
+			guard(mutex)(&chip->mutex);
+			uaudio_dev_cleanup(&uadev[idx]);
+		}
 	}
 }
 
@@ -1183,11 +1190,15 @@ static int uaudio_event_ring_setup(struct snd_usb_substream *subs,
 	er_pa = 0;
 
 	/* event ring */
+	ret = usb_offload_get(subs->dev);
+	if (ret < 0)
+		goto exit;
+
 	ret = xhci_sideband_create_interrupter(uadev[card_num].sb, 1, false,
 					       0, uaudio_qdev->data->intr_num);
 	if (ret < 0) {
 		dev_err(&subs->dev->dev, "failed to fetch interrupter\n");
-		goto exit;
+		goto put_offload;
 	}
 
 	sgt = xhci_sideband_get_event_buffer(uadev[card_num].sb);
@@ -1219,6 +1230,8 @@ static int uaudio_event_ring_setup(struct snd_usb_substream *subs,
 	mem_info->dma = 0;
 remove_interrupter:
 	xhci_sideband_remove_interrupter(uadev[card_num].sb);
+put_offload:
+	usb_offload_put(subs->dev);
 exit:
 	return ret;
 }
@@ -1483,6 +1496,7 @@ static int prepare_qmi_response(struct snd_usb_substream *subs,
 	uaudio_iommu_unmap(MEM_EVENT_RING, IOVA_BASE, PAGE_SIZE, PAGE_SIZE);
 free_sec_ring:
 	xhci_sideband_remove_interrupter(uadev[card_num].sb);
+	usb_offload_put(subs->dev);
 drop_sync_ep:
 	if (subs->sync_endpoint) {
 		uaudio_iommu_unmap(MEM_XFER_RING,
@@ -1528,6 +1542,7 @@ static void handle_uaudio_stream_req(struct qmi_handle *handle,
 	u8 pcm_card_num;
 	u8 pcm_dev_num;
 	u8 direction;
+	struct usb_device *udev = NULL;
 	int ret = 0;
 
 	if (!svc->client_connected) {
@@ -1597,6 +1612,8 @@ static void handle_uaudio_stream_req(struct qmi_handle *handle,
 
 	uadev[pcm_card_num].ctrl_intf = chip->ctrl_intf;
 
+	udev = subs->dev;
+	guard(device)(&udev->dev);
 	if (req_msg->enable) {
 		ret = enable_audio_stream(subs,
 					  map_pcm_format(req_msg->audio_format),
-- 
2.53.0.273.g2a3d683680-goog