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=-3.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 0B626C352A2 for ; Thu, 6 Feb 2020 11:45:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD00C21775 for ; Thu, 6 Feb 2020 11:45:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580989551; bh=ZUspsdQ2rs6/9aUC6SF8t5aeGHcSFv/ALBv58PC074A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=ejLPo/1zdfsJYNEh5t1sT5+0F5Bjej0PswBvTkb28q4gFrW6N2IF47BsA/tsteNxb S1ituFHwpBMQ5t2rsLISQujTqJ9tcR/DJl0tVXz2y2TnbMWYV5644CPupIIFFBuamH TL8ktr7anSUoKiG8dmLBhdmX7nhNv6f81yoWrv7k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727604AbgBFLpv (ORCPT ); Thu, 6 Feb 2020 06:45:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:36140 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727111AbgBFLpu (ORCPT ); Thu, 6 Feb 2020 06:45:50 -0500 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8774120661; Thu, 6 Feb 2020 11:45:48 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1580989549; bh=ZUspsdQ2rs6/9aUC6SF8t5aeGHcSFv/ALBv58PC074A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=uPu+d4vFDSdAjFUF/tQ0LAF3L/O/1K+Wya4hC1we2RMSNaLBOfN7bTDcX1Y/4sAmb 7vCdKTxYPQDvZZuDKriQwSwAFg2dDj3uBqB//6HbKKnNBAZ3WToabUMmBu11AK8rGn GDVXyBRKyP5nuKmcDwhl6i33qbnO2cQ6gIHNNIPg= Date: Thu, 6 Feb 2020 11:45:46 +0000 From: Greg KH To: Johan Hovold Cc: Jakub Nantl , Jonathan Olds , Michael Dreher , linux-usb@vger.kernel.org, stable Subject: Re: [PATCH] USB: serial: ch341: fix receiver regression Message-ID: <20200206114546.GA3275679@kroah.com> References: <20200206111819.20829-1-johan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200206111819.20829-1-johan@kernel.org> Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, Feb 06, 2020 at 12:18:19PM +0100, Johan Hovold wrote: > While assumed not to make a difference, not using the factor 2 prescaler > makes the receiver more susceptible to errors. > > Specifically, there have been reports of problems with devices that > cannot generate a 115200 rate with a smaller error than 2.1% (e.g. > 117647 bps). But this can also be reproduced with a low-speed RS232 > tranceiver at 115200 when the input rate is close to nominal. > > So whenever possible, enable the factor 2 prescaler and halve the > divisor in order to use settings closer to that of the previous > algorithm. > > Fixes: 35714565089e ("USB: serial: ch341: reimplement line-speed handling") > Cc: stable # 5.5 > Reported-by: Jakub Nantl > Tested-by: Jakub Nantl > Signed-off-by: Johan Hovold Reviewed-by: Greg Kroah-Hartman