[PATCH v2] usb: dwc3: gadget: Prevent EPs resource conflict during StartTransfer

[Selvarasu Ganesan <selvarasu.g@samsung.com>]

The below “No resource for ep” warning appears when a StartTransfer
command is issued for bulk or interrupt endpoints in
`dwc3_gadget_ep_enable` while a previous StartTransfer on the same
endpoint is still in progress. The gadget functions drivers can invoke
`usb_ep_enable` (which triggers a new StartTransfer command) before the
earlier transfer has completed. Because the previous StartTransfer is
still active, `dwc3_gadget_ep_disable` can skip the required
`EndTransfer` due to `DWC3_EP_DELAY_STOP`, leading to  the endpoint
resources are busy for previous StartTransfer and warning ("No resource
for ep") from dwc3 driver.

To resolve this, a check is added to `dwc3_gadget_ep_enable` that
checks the `DWC3_EP_TRANSFER_STARTED` flag before issuing a new
StartTransfer. By preventing a second StartTransfer on an already busy
endpoint, the resource conflict is eliminated, the warning disappears,
and potential kernel panics caused by `panic_on_warn` are avoided.

------------[ cut here ]------------
dwc3 13200000.dwc3: No resource for ep1out
WARNING: CPU: 0 PID: 700 at drivers/usb/dwc3/gadget.c:398 dwc3_send_gadget_ep_cmd+0x2f8/0x76c
Call trace:
 dwc3_send_gadget_ep_cmd+0x2f8/0x76c
 __dwc3_gadget_ep_enable+0x490/0x7c0
 dwc3_gadget_ep_enable+0x6c/0xe4
 usb_ep_enable+0x5c/0x15c
 mp_eth_stop+0xd4/0x11c
 __dev_close_many+0x160/0x1c8
 __dev_change_flags+0xfc/0x220
 dev_change_flags+0x24/0x70
 devinet_ioctl+0x434/0x524
 inet_ioctl+0xa8/0x224
 sock_do_ioctl+0x74/0x128
 sock_ioctl+0x3bc/0x468
 __arm64_sys_ioctl+0xa8/0xe4
 invoke_syscall+0x58/0x10c
 el0_svc_common+0xa8/0xdc
 do_el0_svc+0x1c/0x28
 el0_svc+0x38/0x88
 el0t_64_sync_handler+0x70/0xbc
 el0t_64_sync+0x1a8/0x1ac

Fixes: a97ea994605e ("usb: dwc3: gadget: offset Start Transfer latency for bulk EPs")
Cc: stable@vger.kernel.org
Signed-off-by: Selvarasu Ganesan <selvarasu.g@samsung.com>
---

Changes in v2:
- Removed change-id.
- Updated commit message.
Link to v1: https://lore.kernel.org/linux-usb/20251117152812.622-1-selvarasu.g@samsung.com/
---
 drivers/usb/dwc3/gadget.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
index 1f67fb6aead5..8d3caa71ea12 100644
--- a/drivers/usb/dwc3/gadget.c
+++ b/drivers/usb/dwc3/gadget.c
@@ -963,8 +963,9 @@ static int __dwc3_gadget_ep_enable(struct dwc3_ep *dep, unsigned int action)
 	 * Issue StartTransfer here with no-op TRB so we can always rely on No
 	 * Response Update Transfer command.
 	 */
-	if (usb_endpoint_xfer_bulk(desc) ||
-			usb_endpoint_xfer_int(desc)) {
+	if ((usb_endpoint_xfer_bulk(desc) ||
+			usb_endpoint_xfer_int(desc)) &&
+			!(dep->flags & DWC3_EP_TRANSFER_STARTED)) {
 		struct dwc3_gadget_ep_cmd_params params;
 		struct dwc3_trb	*trb;
 		dma_addr_t trb_dma;
-- 
2.34.1