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=-6.7 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 A7EDAC282C0 for ; Wed, 23 Jan 2019 13:58:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 763E32184C for ; Wed, 23 Jan 2019 13:58:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548251914; bh=YaoOwzPhlusepuKK6nNhPrPhHcQyK6Hho8Tqvya0vzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=byq74dMRYEOm9ruzDj6oByBYWxgPS+zlVXNBNnLuSFTuO8m3LTCsM8E/Lk/J7H8As ev7EBP2NMSf4JSZ/y/XIhl0shQ667V0N5VSwpUN7vI4dYa4gSNFKKthxXyhxw0vgRc KKbzvHDeRc856MIcwWLVxAWI3QEv/EE1EIwH1YAM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726140AbfAWN6e (ORCPT ); Wed, 23 Jan 2019 08:58:34 -0500 Received: from mail.kernel.org ([198.145.29.99]:36288 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726104AbfAWN6d (ORCPT ); Wed, 23 Jan 2019 08:58:33 -0500 Received: from localhost (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (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 A04552133D; Wed, 23 Jan 2019 13:58:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548251912; bh=YaoOwzPhlusepuKK6nNhPrPhHcQyK6Hho8Tqvya0vzE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=A+LqxXTMBPOIncX0VazN8sQ3MTgWZs1PtPTuRPZfimeT2HvI5M7N5B4/eh+bKnNYl aUwIlieYt8z/bY1Nc1Q4sfAhK2+BVrBHntTbQtQCCiFDCTgczm9ENDefhqGCgqhJoD Q4mHsNnTQmn5yy9ZBu9q3AVWFTdYjnsStyuTlx6w= Date: Wed, 23 Jan 2019 08:58:31 -0500 From: Sasha Levin To: Johan Hovold Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Nikolaj Fogh , linux-usb@vger.kernel.org Subject: Re: [PATCH AUTOSEL 4.20 025/117] USB: serial: ftdi_sio: use rounding when calculating baud rate divisors Message-ID: <20190123135831.GI202535@sasha-vm> References: <20190108192628.121270-1-sashal@kernel.org> <20190108192628.121270-25-sashal@kernel.org> <20190109082437.GA3389@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20190109082437.GA3389@localhost> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Wed, Jan 09, 2019 at 09:24:37AM +0100, Johan Hovold wrote: >On Tue, Jan 08, 2019 at 02:24:53PM -0500, Sasha Levin wrote: >> From: Nikolaj Fogh >> >> [ Upstream commit 6abd837104a3a8e1cda64fc4d7675f6c3ece9d8b ] >> >> Improve baud-rate generation by using rounding-to-closest instead of >> truncation in divisor calculation. >> >> Results have been verified by logic analyzer on an FT232RT (232BM) chip. >> The following table shows the wanted baud rate, the baud rate obtained >> with the old method (truncation), with the new method (rounding) and the >> baud rate generated by the windows 10 driver. The numbers in parentheses >> is the error. >> >> +- Wanted --+------ Old -------+------ New -------+------ Win -------+ >> |   9600  |   9600 (0.00%)  |   9604 (0.05%)  |   9605 (0.05%)  | >> |   19200   |   19200 (0.00%)  |   19199 (0.01%)  |   19198 (0.01%)  | >> |   38400   |   38395 (0.01%)  |   38431 (0.08%)  |   38394 (0.02%)  | >> |   57600   |   57725 (0.22%)  |   57540 (0.10%)  |   57673 (0.13%)  | >> |  115200   |  115307 (0.09%)  |  115330 (0.11%)  |  115320 (0.10%)  | >> |  921600   |  919963 (0.18%)  |  920386 (0.13%)  |  920810 (0.09%)  | >> |  961200   |  996512 (3.67%)  |  956480 (0.49%)  |  956937 (0.44%)  | >> +-----------+------------------+------------------+------------------+ >> >> The error due to noise in the measurements is in the order of a few >> tenths of a %. As can be seen, the baud rate is significantly improved >> for some rates (e.g. 961200), and corresponds to the output given by the >> windows driver. >> >> The theoretical baud rate has been calculated for all baud rates from 1 >> to 3M, and as expected, the error is centered around 0, with a triangle >> shape instead of a sawtooth, so the maximum error is decreased to half. >> >> Signed-off-by: Nikolaj Fogh >> [ johan: edit commit message slightly ] >> Signed-off-by: Johan Hovold >> Signed-off-by: Sasha Levin > >The stable tag was left out on purpose for this one to avoid breaking >working setups which may have compensated and adapted to this driver >behaviour which has been there since the driver was merged ages ago. I'll drop it, thank you. -- Thanks, Sasha