[PATCH v13 0/4] Support system sleep with offloaded usb transfers

Guan-Yu Lin
2025-05-28T09:09:00Z

Wesley Cheng and Mathias Nyman's USB offload design enables a co-processor
to handle some USB transfers, potentially allowing the system to sleep
(suspend-to-RAM) and save power. However, Linux's System Sleep model halts
the USB host controller when the main system isn't managing any USB
transfers. To address this, the proposal modifies the system to recognize
offloaded USB transfers and manage power accordingly. This way, offloaded
USB transfers could still happen during system sleep (Suspend-to-RAM).

This involves two key steps:
1. Transfer Status Tracking: Propose offload_usage and corresponding apis
drivers could track USB transfers on the co-processor, ensuring the
system is aware of any ongoing activity.
2. Power Management Adjustment: Modifications to the USB driver stack
(xhci host controller driver, and USB device drivers) allow the system to
sleep (Suspend-to-RAM) without disrupting co-processor managed USB
transfers. This involves adding conditional checks to bypass some power
management operations in the System Sleep model.

changelog
----------
Changes in v13:
- Ensure offload_usage is modified only when the device is neither
suspended nor marked as "offload_at_suspend".
- Move lock manipulations into usb_offload_get()/usb_offload_put().
- Cosmetics changes on coding style.

Changes in v12:
- Rebase on TOT.
- Cosmetics changes on coding style.

Changes in v11:
- Use USB subsystem wrappers in usb_offload_get()/usb_offload_put().
- Refine logics and add comment in usb_suspend_both()/usb_resume_both().

Changes in v10:
- Remove unnecessary operations in dwc3 driver.
- Introduce CONFIG_USB_XHCI_SIDEBAND_SUSPEND to enable/disable offloaded
usb transfers during system Suspend-to-RAM.
- Modify the approach to detect offloaded USB transfers when the system
resumes from Suspend-to-RAM.
- Mark sideband activity when sideband interrupters are created/removed.
- Cosmetics changes on coding style.

Changes in v9:
- Remove unnecessary white space change.

Changes in v8:
- Change the runtime pm api to correct the error handling flow.
- Not flushing endpoints of actively offloaded USB devices to avoid
possible USB transfer conflicts.

Changes in v7:
- Remove counting mechanism in struct usb_hcd. The USB device's offload
status will be solely recorded in each related struct usb_device.
- Utilizes `needs_remote_wakeup` attribute in struct usb_interface to
control the suspend flow of USB interfaces and associated USB endpoints.
This addresses the need to support interrupt transfers generated by
offloaded USB devices while the system is suspended.
- Block any offload_usage change during USB device suspend period.

Changes in v6:
- Fix build errors when CONFIG_USB_XHCI_SIDEBAND is disabled.
- Explicitly specify the data structure of the drvdata refereced in
dwc3_suspend(), dwc3_resume().
- Move the initialization of counters to the patches introducing them.

Changes in v5:
- Walk through the USB children in usb_sideband_check() to determine the
sideband activity under the specific USB device.
- Replace atomic_t by refcount_t.
- Reduce logs by using dev_dbg & remove __func__.

Changes in v4:
- Isolate the feature into USB driver stack.
- Integrate with series "Introduce QC USB SND audio offloading support"

Changes in v3:
- Integrate the feature with the pm core framework.

Changes in v2:
- Cosmetics changes on coding style.

[v3] PM / core: conditionally skip system pm in device/driver model
[v2] usb: host: enable suspend-to-RAM control in userspace
[v1] [RFC] usb: host: Allow userspace to control usb suspend flows
---

Guan-Yu Lin (4):
usb: xhci-plat: separate dev_pm_ops for each pm_event
usb: add apis for offload usage tracking
xhci: sideband: add api to trace sideband usage
usb: host: enable USB offload during system sleep

drivers/usb/core/driver.c | 175 +++++++++++++++++++++++++++++-
drivers/usb/core/usb.c | 1 +
drivers/usb/host/Kconfig | 11 ++
drivers/usb/host/xhci-plat.c | 42 ++++++-
drivers/usb/host/xhci-plat.h | 1 +
drivers/usb/host/xhci-sideband.c | 38 +++++++
include/linux/usb.h | 18 +++
include/linux/usb/xhci-sideband.h | 9 ++
8 files changed, 285 insertions(+), 10 deletions(-)

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2.49.0.1164.gab81da1b16-goog