linux-kernel - Re: [PATCH v4] usb: dwc3: gadget: Add 1ms delay after end transfer command without IOC

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Date:   Fri, 3 Mar 2023 11:35:47 -0800
From:   Wesley Cheng <quic_wcheng@...cinc.com>
To:     Thinh Nguyen <Thinh.Nguyen@...opsys.com>
CC:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "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 v4] usb: dwc3: gadget: Add 1ms delay after end transfer
 command without IOC

Hi Thinh,

On 3/1/2023 2:44 PM, Thinh Nguyen wrote:
> On Tue, Feb 28, 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, add
> 
> Can we also note here that we rely on End Transfer command completion
> interrupt on newer versions.
> 
>> the delay back in, 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.
>>
> 
> I think this also needs a Fixes tag.
> 
> Everything else looks good to me.
> 

Thanks for the reviews, Thinh.  Will fix the above and resubmit.

Thanks
Wesley Cheng