linux-kernel - Re: [PATCH] usb: dwc3: ep0: Fix the possible missed request for handling delay STATUS phase

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Date:   Tue, 28 Feb 2017 13:56:39 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>,
        Baolin Wang <baolin.wang@...aro.org>
Cc:     Greg KH <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linaro Kernel Mailman List <linaro-kernel@...ts.linaro.org>,
        Mark Brown <broonie@...nel.org>
Subject: Re: [PATCH] usb: dwc3: ep0: Fix the possible missed request for handling delay STATUS phase


Hi,

Alan Stern <stern@...land.harvard.edu> writes:
>> So I am not sure how the Gadget driver can figure out that it needs to
>> usb_ep_queue() another request for status stage when handling the
>> no-data control?
>
> Gadget drivers already queue status-stage requests for no-data
> control-OUT requests.  The difficulty comes when you want to handle an
> IN request or an OUT request with a data stage.

I don't see a difficulty there. Gadget driver will see wLength and
notice it needs both data and status stages, then it does:

usb_ep_queue(ep0, data_req, GFP_KERNEL);
usb_ep_queue(ep0, status_req, GFP_KERNEL);

Just needs to prepare both requests and queue them both ahead of
time. UDC drivers should hold both requests in their own private list
and process one at a time.

-- 
balbi