linux-kernel - Re: [PATCH v5] usb: dwc3: gadget: Add 1ms delay after end transfer command without IOC

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Date:   Wed, 8 Mar 2023 19:37:32 +0000
From:   Thinh Nguyen <Thinh.Nguyen@...opsys.com>
To:     Wesley Cheng <quic_wcheng@...cinc.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "quic_jackp@...cinc.com" <quic_jackp@...cinc.com>
Subject: Re: [PATCH v5] usb: dwc3: gadget: Add 1ms delay after end transfer
 command without IOC

On Mon, Mar 06, 2023, Wesley Cheng wrote:
> Previously, there was a 100uS delay inserted after issuing an end transfer
> command for specific controller revisions.  This was due to the fact that
> there was a GUCTL2 bit field which enabled synchronous completion of the
> end transfer command once the CMDACT bit was cleared in the DEPCMD
> register.  Since this bit does not exist for all controller revisions and
> the current implementation heavily relies on utizling the EndTransfer
> command completion interrupt, add the delay back in for uses where the
> interrupt on completion bit is not set, and increase the duration to 1ms
> for the controller to complete the command.
> 
> An issue was seen where the USB request buffer was unmapped while the DWC3
> controller was still accessing the TRB.  However, it was confirmed that the
> end transfer command was successfully submitted. (no end transfer timeout)
> In situations, such as dwc3_gadget_soft_disconnect() and
> __dwc3_gadget_ep_disable(), the dwc3_remove_request() is utilized, which
> will issue the end transfer command, and follow up with
> dwc3_gadget_giveback().  At least for the USB ep disable path, it is
> required for any pending and started requests to be completed and returned
> to the function driver in the same context of the disable call.  Without
> the GUCTL2 bit, it is not ensured that the end transfer is completed before
> the buffers are unmapped.
> 
> Fixes: cf2f8b63f7f1 ("usb: dwc3: gadget: Remove END_TRANSFER delay")
> Signed-off-by: Wesley Cheng <quic_wcheng@...cinc.com>
> ---
> Changes in v5:
> - Updated commit text with more details
> - Added fixes tag
> 
> Changes in v4:
> - Updated DWC3 revision check logic to look for !DWC3 based IP (ie DWC32 and
> DWC31 variants)
> - Fixed incorrect delay reference in comments
> 
> Changes in v3:
> - Fixed subject title and modified commit text to reference the new 1ms
> delay
> 
> Changes in v2:
> - Increase delay value to 1ms
> - Make this applicable to DWC32 revisions as well
> 
>  drivers/usb/dwc3/gadget.c | 14 +++++++++++---
>  1 file changed, 11 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c
> index 3c63fa97a680..cf5b4f49c3ed 100644
> --- a/drivers/usb/dwc3/gadget.c
> +++ b/drivers/usb/dwc3/gadget.c
> @@ -1699,6 +1699,7 @@ static int __dwc3_gadget_get_frame(struct dwc3 *dwc)
>   */
>  static int __dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force, bool interrupt)
>  {
> +	struct dwc3 *dwc = dep->dwc;
>  	struct dwc3_gadget_ep_cmd_params params;
>  	u32 cmd;
>  	int ret;
> @@ -1722,10 +1723,13 @@ static int __dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force, bool int
>  	WARN_ON_ONCE(ret);
>  	dep->resource_index = 0;
>  
> -	if (!interrupt)
> +	if (!interrupt) {
> +		if (!DWC3_IP_IS(DWC3) || DWC3_VER_IS_PRIOR(DWC3, 310A))
> +			mdelay(1);
>  		dep->flags &= ~DWC3_EP_TRANSFER_STARTED;
> -	else if (!ret)
> +	} else if (!ret) {
>  		dep->flags |= DWC3_EP_END_TRANSFER_PENDING;
> +	}
>  
>  	dep->flags &= ~DWC3_EP_DELAY_STOP;
>  	return ret;
> @@ -3774,7 +3778,11 @@ void dwc3_stop_active_transfer(struct dwc3_ep *dep, bool force,
>  	 * enabled, the EndTransfer command will have completed upon
>  	 * returning from this function.
>  	 *
> -	 * This mode is NOT available on the DWC_usb31 IP.
> +	 * This mode is NOT available on the DWC_usb31 IP.  In this
> +	 * case, if the IOC bit is not set, then delay by 1ms
> +	 * after issuing the EndTransfer command.  This allows for the
> +	 * controller to handle the command completely before DWC3
> +	 * remove requests attempts to unmap USB request buffers.
>  	 */
>  
>  	__dwc3_stop_active_transfer(dep, force, interrupt);

Acked-by: Thinh Nguyen <Thinh.Nguyen@...opsys.com>

Thanks,
Thinh