linux-kernel - [PATCH v3] usb: dwc3: gadget: Fix TRB reclaim logic for short transfers and ZLPs

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Message-ID:
 <AM8PR06MB7521A29A8863C838B54987B6BC7BA@AM8PR06MB7521.eurprd06.prod.outlook.com>
Date: Wed, 25 Jun 2025 07:49:16 +0000
From: SCHNEIDER Johannes <johannes.schneider@...ca-geosystems.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC: Pengutronix Kernel Team <kernel@...gutronix.de>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	GEO-CHHER-bsp-development <bsp-development.geo@...ca-geosystems.com>, Greg
 Kroah-Hartman <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: [PATCH v3] usb: dwc3: gadget: Fix TRB reclaim logic for short
 transfers and ZLPs

Commit 96c7bf8f6b3e ("usb: dwc3: gadget: Cleanup SG handling") updated
the TRB reclaim path to use the TRB CHN (Chain) bit to determine whether
a TRB was part of a chain. However, this inadvertently changed the
behavior of reclaiming the final TRB in some scatter-gather or short
transfer cases.

In particular, if the final TRB did not have the CHN bit set, the
cleanup path could incorrectly skip clearing the HWO (Hardware Own)
bit, leaving stale TRBs in the ring. This resulted in broken data
transfer completions in userspace, notably for MTP over FunctionFS.

Fix this by unconditionally clearing the HWO bit during TRB reclaim,
regardless of the CHN bit state. This restores correct behavior
especially for transfers that require ZLPs or end on non-CHN TRBs.

Fixes 61440628a4ff ("usb: dwc3: gadget: Cleanup SG handling")
Signed-off-by: Johannes Schneider <johannes.schneider@...ca-geosystems.com>
Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: <stable@...r.kernel.org> # v6.13
---
v3: no changes, re-submission as single patch, with Cc stable
v2: no changes to the patch, "faulty" re-submission
v1: initial submission as part of a series
Link: https://lore.kernel.org/lkml/AM8PR06MB7521CFF1CD8A93622A537EEDBC78A@AM8PR06MB7521.eurprd06.prod.outlook.com/

 drivers/usb/dwc3/gadget.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 321361288935..99fbd29d8f46 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -3516,7 +3516,7 @@ static int dwc3_gadget_ep_reclaim_completed_trb(struct dwc3_ep *dep,
 	 * We're going to do that here to avoid problems of HW trying
 	 * to use bogus TRBs for transfers.
 	 */
-	if (chain && (trb->ctrl & DWC3_TRB_CTRL_HWO))
+	if (trb->ctrl & DWC3_TRB_CTRL_HWO)
 		trb->ctrl &= ~DWC3_TRB_CTRL_HWO;

 	/*
-- 
2.43.0