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 48739C636D6 for ; Thu, 2 Feb 2023 14:53:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232541AbjBBOxS (ORCPT ); Thu, 2 Feb 2023 09:53:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59496 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232300AbjBBOwy (ORCPT ); Thu, 2 Feb 2023 09:52:54 -0500 Received: from netrider.rowland.org (netrider.rowland.org [192.131.102.5]) by lindbergh.monkeyblade.net (Postfix) with SMTP id 972B659EF for ; Thu, 2 Feb 2023 06:52:37 -0800 (PST) Received: (qmail 525724 invoked by uid 1000); 2 Feb 2023 09:52:36 -0500 Date: Thu, 2 Feb 2023 09:52:36 -0500 From: Alan Stern To: Dan Scally Cc: Thinh Nguyen , "linux-usb@vger.kernel.org" , rogerq@kernel.org Subject: Re: Explicit status phase for DWC3 Message-ID: References: <9ce226b4-90c6-94c4-a5ad-bd623409bc51@ideasonboard.com> <20230126002017.tbxc3j6xdgplncfs@synopsys.com> <20230126193131.ifaj7arsrrgesjh5@synopsys.com> <20230126235704.62d32y7y4sa4mmry@synopsys.com> <43b077ad-c8cd-bb49-134d-1bd66bed0b84@ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <43b077ad-c8cd-bb49-134d-1bd66bed0b84@ideasonboard.com> Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, Feb 02, 2023 at 10:12:45AM +0000, Dan Scally wrote: > (+CC roger as the author of the USB_GADGET_DELAYED_STATUS mechanism) > > On 26/01/2023 23:57, Thinh Nguyen wrote: > > 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/ I'm in favor of the explicit_status approach from [2]. In fact, there was a whole series of patches impementing this, and I don't think any of them were merged. Keep in mind that there are two separate issues here: Status/data stage for a control-IN or 0-length control-OUT transfer. Status stage for a non-0-length control-OUT transfer. The USB_GADGET_DELAYED_STATUS mechanism was meant to help with the first, not the second. explicit_status was meant to help with the second; it may be able to help with both. Alan Stern