Hoi,
This patch series fixes a subtle regression introduced in the recent scatter-gather cleanup for the DWC3 USB gadget driver, and follows up with two clean-up patches to simplify and clarify related logic.
Background:
Commit 61440628a4ff ("usb: dwc3: gadget: Cleanup SG handling") removed some redundant state tracking in the DWC3 gadget driver, including how scatter-gather TRBs are reclaimed after use. However, the reclaim logic began relying on the TRB CHN (chain) bit to determine whether TRBs belonged to a chain — which led to missed TRB reclamation in some cases.
This broke userspace-facing protocols like MTP (Media Transfer Protocol) when used via FunctionFS, causing incomplete transfers due to skipped zero-length packets (ZLPs) or improperly reclaimed short TRBs.
The "offending" chunk from 61440628a4ff: 80 ret = dwc3_gadget_ep_reclaim_completed_trb(dep, req, 81 - trb, event, status, true); 82 + trb, event, status, 83 + !!(trb->ctrl & DWC3_TRB_CTRL_CHN));
Patch 1 fixes the issue by ensuring the HWO bit is always cleared on reclaimed TRBs, regardless of the CHN bit.
Patches 2 and 3 follow up with simplifications: - Patch 2 removes the now-redundant `chain` argument to the reclaim function - Patch 3 simplifies the logic in `dwc3_needs_extra_trb()` to make the conditions easier to read and maintain
All three patches have been tested on a imx8mp based hardware, with userspace MTP (viveris/uMTP-Responder) over FunctionFS and resolve the regression while preserving the recent cleanup work.
Signed-off-by: Johannes Schneider johannes.schneider@leica-geosystems.com --- Changes in v2: - dropped Patch 3, as it did change the logic - CC to stable - Link to v1: https://lore.kernel.org/r/20250621-dwc3-fix-gadget-mtp-v1-0-a45e6def71bb@lei...
--- Johannes Schneider (2): usb: dwc3: gadget: Fix TRB reclaim logic for short transfers and ZLPs usb: dwc3: gadget: Simplify TRB reclaim logic by removing redundant 'chain' argument
drivers/usb/dwc3/gadget.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) --- base-commit: d0c22de9995b624f563bc5004d44ac2655712a56 change-id: 20250621-dwc3-fix-gadget-mtp-3c09a6ab84c6
Best regards,