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 AF9B1C3B186 for ; Tue, 11 Feb 2020 12:30:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 83F0D20842 for ; Tue, 11 Feb 2020 12:30:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581424211; bh=UOl+tQ/zZd+KwI4FO4cTDXiLUcocDiU1LoF+UqO99S4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=l7KnFgujo7x8NGHEY487cxnwcQhVc2bnJUKnbvJ96664J1GDACoufIrB1Qylj30VH NS/mjXucgQyQ6mfHc2iV3q19QMIrSpzrytCy9W8Nh3NWWAk5r3GPXLRrgW7au7UW33 qsun1yuHa+s5svGuuHRuHExm2tzrgZgAfHCYH3Cg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728812AbgBKMaL (ORCPT ); Tue, 11 Feb 2020 07:30:11 -0500 Received: from mail.kernel.org ([198.145.29.99]:51908 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728467AbgBKMaK (ORCPT ); Tue, 11 Feb 2020 07:30:10 -0500 Received: from localhost (unknown [209.37.97.194]) (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 8CD5820714; Tue, 11 Feb 2020 12:30:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581424209; bh=UOl+tQ/zZd+KwI4FO4cTDXiLUcocDiU1LoF+UqO99S4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=TyAGYzmBk647Xic8+Af5jY50tMRYt9H5bHtn6wsE10WXBTvj6piI1yGy8Z6MCj+ZS ansTqCI6m6WsvLaA3okd2k0EYZxvvCWq6Iq7nJE8mUUSf4uxk4FoLXexYzdDYJU1te 3efECLAoHJQaFnkycH7+U+jvYJPstPYkJ8I0fcYI= Date: Tue, 11 Feb 2020 04:30:09 -0800 From: Greg Kroah-Hartman To: Geert Uytterhoeven Cc: Eugeniu Rosca , "open list:SERIAL DRIVERS" , Linux-Renesas , Wolfram Sang , Yoshihiro Shimoda , Ulrich Hecht , "George G . Davis" , Andrew Gabbasov , Jiada Wang , Yuichi Kusakabe , Yasushi Asano , Linux Kernel Mailing List , Jiri Slaby , Fukui Yohhei , Torii Kenichi , Magnus Damm , "Michael Kerrisk (man-pages)" , linux-man@vger.kernel.org Subject: Re: [PATCH] serial: sh-sci: Support custom speed setting Message-ID: <20200211123009.GB1858119@kroah.com> References: <20200129161955.30562-1-erosca@de.adit-jv.com> <20200210205735.GB1347752@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 11, 2020 at 09:15:02AM +0100, Geert Uytterhoeven wrote: > Hi Greg, > > CC man > > On Mon, Feb 10, 2020 at 9:57 PM Greg Kroah-Hartman > wrote: > > On Thu, Jan 30, 2020 at 01:32:50PM +0100, Geert Uytterhoeven wrote: > > > On Wed, Jan 29, 2020 at 5:20 PM Eugeniu Rosca wrote: > > > > From: Torii Kenichi > > > > > > > > This patch is necessary to use BT module and XM module with DENSO TEN > > > > development board. > > > > > > > > This patch supports ASYNC_SPD_CUST flag by ioctl(TIOCSSERIAL), enables > > > > custom speed setting with setserial(1). > > > > > > > > The custom speed is calculated from uartclk and custom_divisor. > > > > If custom_divisor is zero, custom speed setting is invalid. > > > > > > > > Signed-off-by: Torii Kenichi > > > > [erosca: rebase against v5.5] > > > > Signed-off-by: Eugeniu Rosca > > > > > > Thanks for your patch! > > > > > > While this seems to work fine[*], I have a few comments/questions: > > > 1. This feature seems to be deprecated: > > > > > > sh-sci e6e68000.serial: setserial sets custom speed on > > > ttySC1. This is deprecated. > > > > > > 2. As the wanted speed is specified as a divider, the resulting speed > > > may be off, cfr. the example for 57600 below. > > > Note that the SCIF device has multiple clock inputs, and can do > > > 57600 perfectly if the right crystal has been fitted. > > > > > > 3. What to do with "[PATCH/RFC] serial: sh-sci: Update uartclk based > > > on selected clock" (https://patchwork.kernel.org/patch/11103703/)? > > > Combined with this, things become pretty complicated and > > > unpredictable, as uartclk now always reflect the frequency of the > > > last used base clock, which was the optimal one for the previously > > > used speed.... > > > > > > I think it would be easier if we just had an API to specify a raw speed. > > > Perhaps that already exists? > > > > Yes, see: > > http://www.panix.com/~grante/arbitrary-baud.c > > Thanks a lot!! > This must be one of the most guarded secrets of serial port programming ;-) It really is, I have to look it up each time it comes up :( > Implemented since 2006, commit edc6afc5496875a6 ("[PATCH] tty: switch to > ktermios and new framework"), not documented in today's man-pages. yeah, serial port control really needs to be documented better, there's all sorts of nice ways of controlling them that people don't seem to know about. I used to have a link to a bunch of online examples, but can't seem to find that anymore either. Ugh, another thing for the long TODO file... greg k-h