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 X-Spam-Level: X-Spam-Status: No, score=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 82DDAC433E0 for ; Sun, 21 Jun 2020 14:09:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 614412491C for ; Sun, 21 Jun 2020 14:09:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730080AbgFUOJS (ORCPT ); Sun, 21 Jun 2020 10:09:18 -0400 Received: from netrider.rowland.org ([192.131.102.5]:38403 "HELO netrider.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1730022AbgFUOJR (ORCPT ); Sun, 21 Jun 2020 10:09:17 -0400 Received: (qmail 107959 invoked by uid 1000); 21 Jun 2020 10:09:16 -0400 Date: Sun, 21 Jun 2020 10:09:16 -0400 From: Alan Stern To: Sid Spry Cc: linux-usb@vger.kernel.org Subject: Re: Unable to Use Isochronous Behavior w/ Isoc Endpoint in FunctionFC Message-ID: <20200621140916.GB107361@rowland.harvard.edu> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Sat, Jun 20, 2020 at 10:38:33PM -0500, Sid Spry wrote: > When I was using a repurposed audio device I had to set an alternate mode. Is > that related to the issue here? The alternate mode seems to be a relic of the > descriptor layout before I dropped the device class and substituted my own > driver. The current descriptors specify no alternate modes. I don't know much about FunctionFS, so I can't help with your main question about isochronous packets not being dropped. But I can explain this. In the USB-2.0 spec, at the end of section 5.6.3 the text says: All device default interface settings must not include any isochronous endpoints with non-zero data payload sizes (specified via wMaxPacketSize in the endpoint descriptor). Alternate interface settings may specify non-zero data payload sizes for isochronous endpoints. That's why you had to select an alternate setting before transferring any isochronous data. Any isochronous endpoint in altsetting 0 must have its maxpacket size set to 0. Alan Stern