Re: [PATCH v2] usb: dwc3: core: Fix RAM interface getting stuck during enumeration

On Thu, Aug 06, 2026, Krishna Kurapati wrote:
> During plug-in/plug-out test cases, it is sometimes seen that no events
> are generated by the controller and all CSR register reads give "0" and
> CSR_Timeout bit gets set indicating that CSR reads/writes are timing out
> or timed out.
> 
> The issue comes up on different instnaces of enumeration on different
> platforms. On SM8550, the debug log is as follows:
> 
> Prepared a TRB on ep0out and did start transfer to get set
> address request from host:
> 
> <...>-7191    [000] D..1.    66.421006: dwc3_gadget_ep_cmd: ep0out:
> cmd 'Start Transfer' [406] params 00000000 efffa000 00000000 -->
> status: Successful
> 
> <...>-7191    [000] D..1.    66.421196: dwc3_event: event (0000c040):
> ep0out: Transfer Complete (sIL) [Setup Phase]
> 
> <...>-7191    [000] D..1.    66.421197: dwc3_ctrl_req: Set
> Address(Addr = 01)
> 
> An XFER NRDY is received on ep0in for zero length status phase and
> a Start Transfer was done on ep0in with 0-length packet in 2 Stage
> status phase:
> 
> <...>-7191    [000] D..1.    66.421249: dwc3_event: event (000020c2):
> ep0in: Transfer Not Ready [00000000] (Not Active) [Status Phase]
> 
> <...>-7191    [000] D..1.    66.421266: dwc3_prepare_trb: ep0in: trb
> ffffffc00fcfd000 (E0:D0) buf 00000000efffa000 size 0 ctrl 00000c33
> sofn 00000000 (HLcs:SC:status2)
> 
> <...>-7191    [000] D..1.    66.421387: dwc3_gadget_ep_cmd: ep0in: cmd
> 'Start Transfer' [406] params 00000000 efffa000 00000000 -->status:
> Successful
> 
> A bus reset was then received directly after 500 msec. Software never
> got the cmd complete for the start transfer done in status phase. Here
> the RAM interface is stuck. So host issues a bus reset as link is
> idle for 500 msec:
> 
> <...>-7191    [000] D..1.    66.935603: dwc3_event: event (00000101):
> Reset [U0]
> 
> Then software sees that it is in status phase and we issue an ENDXFER
> on ep0in and it gets timedout waiting for the CMDACT to go '0':
> 
> <...>-7191    [000] D..1.    66.958249: dwc3_gadget_ep_cmd: ep0in: cmd
> 'End Transfer' [10508] params 00000000 00000000 00000000 --> status:
> Timed Out
> 
> Upon debug with Synopsys, the root cause is as follows:
> 
> During any transfer, if the data is not successfully transmitted,
> then a Done (with failure) handshake is returned, so that the BMU
> can re-attempt the same data again by rewinding its data pointers.
> 
> But, if the USB IN is a 0-length payload (which is what is happening
> in this case - 2 stage status phase of set_address), then there is no
> need to rewind the pointers and the Done (with failure) handshake is
> not returned for failure case. This keeps the Request-Done interface
> busy till the next Done handshake. The MAC sends the 0-length payload
> again when the host requests. If the transmission is successful this
> time, the Done (with success) handshake is provided back. Otherwise,
> it repeats the same steps again.
> 
> If the cable is disconnected or if the Host aborts the transfer on 3
> consecutive failed attempts, the Request-Done handshake is not
> complete. This keeps the interface busy.
> 
> The subsequent RAM access cannot proceed until the above pending
> transfer is complete. This results in failure of any access to RAM
> address locations. Many of the EndPoint commands need to access the
> RAM and they would fail to complete successfully.
> 
> Furthermore when cable removal happens, this would not generate a
> disconnect event and the "connected" flag remains true always blockin
> suspend.
> 
> Synopsys confirmed that the issue is present on all USB3 devices and
> as a workaround, suggested to re-initialize device mode.
> 
> Signed-off-by: Krishna Kurapati <[email protected]>
> ---
> This series has only been compile tested. The issue was reproduced
> easily with a certain kind of cable and CDP port of AMD based Lenovo
> laptop. I don't have access to the cable currently and hence only
> compile testing the fix for now. But the issue has popped up on OEM
> testing as well.
> 
> Changes in v2:
> - Implemented gadget recovery mechanism during gadget_ep_cmd instead of
> handling this issue only during disconnect.
> 
> Link to RFC:
> https://urldefense.com/v3/__https://lore.kernel.org/all/[email protected]/__;!!A4F2R9G_pg!eBUzMlnEP2TK2HfbFZJaL1FQ2kLpCTkQgpKJf1nK616krwl1F5bq2LDIEAHwGpFj1ooH8y6Qzo1zikdXo0CszO5YCBQUTRhswkwqXA$ 
> ---
>  drivers/usb/dwc3/gadget.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index fa0f16ffafef..7aa290a804cc 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -283,6 +283,17 @@ int dwc3_send_gadget_generic_command(struct dwc3 *dwc, unsigned int cmd,
>  	return ret;
>  }
>  
> +static int dwc3_gadget_soft_disconnect(struct dwc3 *dwc);
> +static int dwc3_gadget_soft_connect(struct dwc3 *dwc);
> +
> +static void dwc3_gadget_recover(struct dwc3 *dwc)
> +{
> +	dev_warn(dwc->dev, "controller dead... triggering soft reconnect\n");
> +	dwc3_gadget_soft_disconnect(dwc);
> +	udelay(100);
> +	dwc3_gadget_soft_connect(dwc);
> +}
> +
>  /**
>   * dwc3_send_gadget_ep_cmd - issue an endpoint command
>   * @dep: the endpoint to which the command is going to be issued
> @@ -432,6 +443,23 @@ int dwc3_send_gadget_ep_cmd(struct dwc3_ep *dep, unsigned int cmd,
>  		cmd_status = -ETIMEDOUT;
>  	}
>  
> +	/*
> +	 * STAR 5001544 - In some situations, like the cable is
> +	 * disconnected or if the Host aborts the transfer on 3
> +	 * consecutive failed attempts, the Request-Done handshake is not
> +	 * complete. This keeps the RAM interface busy.
> +	 *
> +	 * The subsequent RAM access cannot proceed until the pending
> +	 * transfer is complete. This results in failure of any access
> +	 * to RAM address locations. Many of the EndPoint commands need to
> +	 * access the RAM and they would fail to complete successfully.
> +	 *
> +	 * If the depcmd doesn't match the actual command, trigger controller
> +	 * recovery.
> +	 */
> +	if (DWC3_DEPCMD_CMD(reg) != DWC3_DEPCMD_CMD(cmd))
> +		dwc3_gadget_recover(dwc);
> +
>  skip_status:
>  	trace_dwc3_gadget_ep_cmd(dep, cmd, params, cmd_status);
>  
> 
> ---
> base-commit: 5d5fd841c34649f1b09220fe58e59dffd61c447d
> change-id: 20260803-ram-interface-code-12c624709732
> 
> Best regards,
> --  
> Krishna Kurapati <[email protected]>
> 

Liu is also working on a controller recovery flow here:
https://lore.kernel.org/linux-usb/anZYnWfDlNPRQBq3@vbox/T/#t

Maybe you can review my feedback there also.

Thanks,
Thinh