From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 630B6C61DA4 for ; Thu, 2 Feb 2023 10:12:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232245AbjBBKMz (ORCPT ); Thu, 2 Feb 2023 05:12:55 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50210 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231949AbjBBKMw (ORCPT ); Thu, 2 Feb 2023 05:12:52 -0500 Received: from perceval.ideasonboard.com (perceval.ideasonboard.com [IPv6:2001:4b98:dc2:55:216:3eff:fef7:d647]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B07D71996 for ; Thu, 2 Feb 2023 02:12:51 -0800 (PST) Received: from [192.168.0.43] (cpc141996-chfd3-2-0-cust928.12-3.cable.virginm.net [86.13.91.161]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id 90381505; Thu, 2 Feb 2023 11:12:48 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1675332768; bh=2jYANZg6skmoVk4M7HuBZgtlDydISLaFPT+EvzB14SM=; h=Date:To:Cc:References:From:Subject:In-Reply-To:From; b=AzydEKdiAn0QU1zCB/c4kiH5tIGekRhaN+58o638PdaNiBw0GwJ1145hVanHGoDCz cqQ+U9ANrmnBmfEJRwpDj5cTOAzfAyntfdu5w2EyVhhsX8jiwx9Vmpi8iuwny4YW/P 33v144bZ1ZPtbqWboej0wleYh6oPi2s78RKEw9PE= Message-ID: <43b077ad-c8cd-bb49-134d-1bd66bed0b84@ideasonboard.com> Date: Thu, 2 Feb 2023 10:12:45 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.4.2 Content-Language: en-US To: Thinh Nguyen , Alan Stern Cc: "linux-usb@vger.kernel.org" , rogerq@kernel.org References: <9ce226b4-90c6-94c4-a5ad-bd623409bc51@ideasonboard.com> <20230126002017.tbxc3j6xdgplncfs@synopsys.com> <20230126193131.ifaj7arsrrgesjh5@synopsys.com> <20230126235704.62d32y7y4sa4mmry@synopsys.com> From: Dan Scally Subject: Re: Explicit status phase for DWC3 In-Reply-To: <20230126235704.62d32y7y4sa4mmry@synopsys.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org (+CC roger as the author of the USB_GADGET_DELAYED_STATUS mechanism) On 26/01/2023 23:57, Thinh Nguyen wrote: > On Thu, Jan 26, 2023, Alan Stern wrote: >> On Thu, Jan 26, 2023 at 07:31:34PM +0000, Thinh Nguyen wrote: >>> On Thu, Jan 26, 2023, Dan Scally wrote: >>>> Hi Thinh >>>> >>>> On 26/01/2023 00:20, Thinh Nguyen wrote: >>>>> On Tue, Jan 24, 2023, Dan Scally wrote: >>>>>> Hi Thinh >>>>>> >>>>>> >>>>>> I'm trying to update the DWC3 driver to allow the status phase of a >>>>>> transaction to be explicit; meaning the gadget driver has the choice to >>>>>> either Ack or Stall _after_ the data phase so that the contents of the data >>>>>> phase can be validated. I thought that I should be able to achieve this by >>>>>> preventing dwc3_ep0_xfernotready() from calling dwc3_ep0_do_control_status() >>>>>> (relying on an "explicit_status" flag added to the usb_request to decide >>>>>> whether or not to do so) and then calling it manually later once the data >>>>>> phase was validated by the gadget driver (or indeed userspace). A very >>>>>> barebones version of my attempt to do that looks like this: >>>>>> >>>>> We shouldn't do this. At the protocol level, there must be better ways >>>>> to do handshake than relying on protocol STALL _after_ the data stage. >>>>> Note that not all controllers support this. >>>> >>>> Maybe I'm misunderstanding, but isn't this how the USB spec expects it to >>>> work? Reading "Reporting Status Results (8.5.3.1)" in the USB 2.0 spec for >>>> the status stage in a control write it says "The function responds with >>>> either a handshake or a zero-length data packet to indicate its current >>>> status", and the handshake can be either STALL or NAK. If we can't do this, >>>> how else can we indicate to the host that the data sent during a control out >>>> transfer is in some way invalid? >>>> >>> My concern is from the documentation note[*] added from this commit: >>> 579c2b46f74 ("USB Gadget: documentation update") >> When the gadget subsystem was originally designed, it made no allowance >> for sending a STALL in the status stage. The UDC drivers existing at >> that time would automatically send their own zero-length status packet >> when the control data was received. >> >> Drivers written since then have copied that approach. They had to, if >> they wanted to work with the existing gadget drivers. So the end result >> is that fully supporting status stalls will require changing pretty much >> every UDC driver. >> >> As for whether the UDC hardware has support... I don't know. Some of >> the earlier devices might not, but I expect that the more popular recent >> designs would provide a way to do it. >> > Right, it's just a bit concerning when the document also noted this: > "Note that some USB device controllers disallow protocol stall responses > in some cases." > > It could be just for older controllers as you mentioned. > > > Hi Dan, > > We should already have this mechanism in place to do protocol STALL. > Please look into delayed_status and set halt. Thanks; I tried this by returning USB_GADGET_DELAYED_STATUS from the function's .setup() callback and later (after userspace checks the data packet) either calling usb_ep_queue() or usb_ep_set_halt() and it does seem to be working. This surprises me, as my understanding was that the purpose of USB_GADGET_DELAYED_STATUS  is to pause all control transfers including the data phase to give the function driver enough time to queue a request (and possibly only for specific requests). Regardless though I think the conclusion from previous discussions on this topic (see [1] for example) was that we don't want to rely on USB_GADGET_DELAYED_STATUS to do this which is why I had avoided it in the first place. A colleague made a series [2] some time ago that adds a flag to usb_request which function drivers can set when queuing the data phase request. UDC drivers then read that flag to decide whether to delay the status phase until after another usb_ep_queue(), and that's what I'm trying to implement here. [1] https://lkml.org/lkml/2018/10/10/138 [2] https://patchwork.kernel.org/project/linux-usb/patch/20190124030228.19840-5-paul.elder@ideasonboard.com/ > > Regarding this question: > How else can we indicate to the host that the data sent during a > control out transfer is in some way invalid? > > Typically there should be another request checking for the command > status. I suppose if we use protocol STALL, you only need to send status > request check on error cases. > > Thanks, > Thinh