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,URIBL_BLOCKED,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 DFC07C433E1 for ; Thu, 2 Jul 2020 04:11:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C38512071A for ; Thu, 2 Jul 2020 04:11:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726371AbgGBEL4 (ORCPT ); Thu, 2 Jul 2020 00:11:56 -0400 Received: from bmailout1.hostsharing.net ([83.223.95.100]:45731 "EHLO bmailout1.hostsharing.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725857AbgGBEL4 (ORCPT ); Thu, 2 Jul 2020 00:11:56 -0400 Received: from h08.hostsharing.net (h08.hostsharing.net [IPv6:2a01:37:1000::53df:5f1c:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "*.hostsharing.net", Issuer "COMODO RSA Domain Validation Secure Server CA" (not verified)) by bmailout1.hostsharing.net (Postfix) with ESMTPS id 07030300011B9; Thu, 2 Jul 2020 06:11:53 +0200 (CEST) Received: by h08.hostsharing.net (Postfix, from userid 100393) id BC3492ED3E2; Thu, 2 Jul 2020 06:11:52 +0200 (CEST) Date: Thu, 2 Jul 2020 06:11:52 +0200 From: Lukas Wunner To: Serge Semin Cc: Daniel Winkler , Serge Semin , linux-serial@vger.kernel.org, linux-mediatek@lists.infradead.org, Alexey Malahov , BlueZ , chromeos-bluetooth-upstreaming , stable@vger.kernel.org, abhishekpandit@chromium.org, Aaron Sierra , Andy Shevchenko , Greg Kroah-Hartman , Jiri Slaby , Vignesh Raghavendra , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/1] Revert "serial: 8250: Fix max baud limit in generic 8250 port" Message-ID: <20200702041152.e5csvbodojzwnagx@wunner.de> References: <20200701211337.3027448-1-danielwinkler@google.com> <20200701223713.gavale4aramu3xnb@mobilestation> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200701223713.gavale4aramu3xnb@mobilestation> User-Agent: NeoMutt/20170113 (1.7.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 02, 2020 at 01:37:13AM +0300, Serge Semin wrote: > 1) Add a new capability like UART_CAP_NO16DIV and take it into account > in the serial8250_get_baud_rate() method. > > I don't have a documentation for the Mediatek UART port, but it seems to me > that that controller calculates the baud rate differently from the standard > 8250 port. A standard 8250 port does that by the next formulae: > baud = uartclk / (16 * divisor). > While it seems to me that the Mediatek port uses the formulae like: > baud = uartclk / divisor. (Please, correct me if I'm wrong) 8250_bcm2835aux.c seems to suffer from a similar issue and solves it like this in the ->probe hook: /* the HW-clock divider for bcm2835aux is 8, * but 8250 expects a divider of 16, * so we have to multiply the actual clock by 2 * to get identical baudrates. */ up.port.uartclk = clk_get_rate(data->clk) * 2; > 2) Manually call serial8250_do_set_divisor() in the custom set_termios() > callback. > > Just add the uart_update_timeout() and serial8250_do_set_divisor() methods > invocation into the mtk8250_set_termios() function, which the original commit > 81bb549fdf14 ("serial: 8250_mtk: support big baud rate") author should have > done in the first place. That sound preferable as adding new quirks into core code feels like a case of midlayer fallacy: https://blog.ffwll.ch/2016/12/midlayers-once-more-with-feeling.html Thanks, Lukas