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Message-ID: <8209aefa-5ab3-43dd-94f5-350e6d38cec2@rowland.harvard.edu>
Date: Thu, 24 Aug 2023 22:08:53 -0400
From: Alan Stern <stern@...land.harvard.edu>
To: Andrey Konovalov <andreyknvl@...il.com>
Cc: Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Felipe Balbi <balbi@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
USB list <linux-usb@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: dwc3: unusual handling of setup requests with wLength == 0
On Fri, Aug 25, 2023 at 03:36:36AM +0200, Andrey Konovalov wrote:
> So to summarize the issue wrt the 0-length requests:
>
> 1. UDC drivers must always delay the status stage for 0-length
> requests until the gadget driver queues an empty request.
Any request, not necessarily empty (although it should be). The request
queued by the gadget driver _is_ the Status stage response; in this
situation the UDC driver doesn't create one automatically.
> 2. Many UDC drivers do not do this, and only delay the status stage
> when USB_GADGET_DELAYED_STATUS is returned from ->setup(). Some
> drivers also assume that only a SET_CONFIGURATION request can be
> delayed.
>
> 3. All such UDC drivers should be fixed and USB_GADGET_DELAYED_STATUS
> should be contained within the composite framework.
>
> 4. Fixing all such UDC drivers is a non-trivial amount of work, but
> this is the goal to strive towards.
>
> Alan, would it be acceptable if I add custom handling of
> USB_GADGET_DELAYED_STATUS to Raw Gadget in the meantime? It would be
Sure. It's your driver; do whatever you want with it. :-)
> great to keep it at least somewhat working with dwc3. I can also do it
> for GadgetFS, if you think it's a good idea.
I suspect gadgetfs doesn't need it. But go ahead and look through the
code to check for yourself; I might be wrong.
> I can also add some clarifying comments for USB_GADGET_DELAYED_STATUS
> and ->setup() to hopefully avoid having new UDC drivers being added
> with the same issue (e.g. cdns2 and renesas_usbf with the same issue
> were added just recently).
Good idea, although mistakes like this tend to propagate more through
copy-and-paste than by failures of documentation.
> Maybe it's also a good idea to add a checkpatch.pl check for using
> USB_GADGET_DELAYED_STATUS in UDC drivers. Or maybe ask Greg to keep an
> eye out for this?
I wouldn't try to modify checkpatch.pl.
Alan Stern
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