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=-5.2 required=3.0 tests=BAYES_00, 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 B1D75C432BE for ; Tue, 24 Aug 2021 15:07:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9694860231 for ; Tue, 24 Aug 2021 15:07:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238136AbhHXPHn (ORCPT ); Tue, 24 Aug 2021 11:07:43 -0400 Received: from wtarreau.pck.nerim.net ([62.212.114.60]:39640 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238118AbhHXPHl (ORCPT ); Tue, 24 Aug 2021 11:07:41 -0400 Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 17OF6qgw026318; Tue, 24 Aug 2021 17:06:52 +0200 Date: Tue, 24 Aug 2021 17:06:52 +0200 From: Willy Tarreau To: Johan Hovold Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Paul =?iso-8859-1?B?R3L232Vs?= Subject: Re: [PATCH] Revert "USB: serial: ch341: fix character loss at high transfer rates" Message-ID: <20210824150652.GA25488@1wt.eu> References: <20210824121926.19311-1-johan@kernel.org> <20210824123232.GA25435@1wt.eu> 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) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ removed Cc stable for the rest of the discussion ] On Tue, Aug 24, 2021 at 03:25:16PM +0200, Johan Hovold wrote: > Zero-length packets are used to indicate completion of bulk transfers > that are multiples of the endpoint max-packet size (as per the USB > spec). Without those the host controller driver doesn't now that the > transfer is complete and that it should call the driver completion > callback (and instead waits for the other completion conditions). Thanks for the explanation. I guess that in my case, given that the serial port would emit lots of continuous data (e.g. "find /" or "dmesg"), there's always something pending and the risk that it ends exactly on a 64-byte boundary remained low and never happened in practice. > It may be possible to configure the device to send ZLPs somehow but > since there's no public documentation for the protocol that may require > some reverse engineering. I totally understand. I'll drop my CH34x adapters and try to figure more suitable ones (i.e. some which work *by default* under Linux). Their small footprint was nice but without doc they're only usable for low speeds :-/ Thanks! Willy