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

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Date:   Thu, 02 Mar 2017 12:43:31 +0200
From:   Felipe Balbi <balbi@...nel.org>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     Baolin Wang <baolin.wang@...aro.org>,
        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:
>> 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);
>
> The main difficulty is that all the gadget/function drivers will have 
> to be audited to add the status requests.

yeah, that's a given and was also mentioned in this thread somewhere.

>> 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.
>
> Or the gadget driver should queue the status request after the 
> data stage has been fully processed, in the case of an OUT transfer.

right, we could use ->complete() for that.

> There is still a possible race.  The host might send another SETUP
> packet before the status request has been queued, or after it has been

we should also have code for this race since it would happen with
USB_GADGET_DELAYED_STATUS.

> queued but before the UDC driver has completed it.  (Of course, that's 
> already true now for the data request...)

right

-- 
balbi

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