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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 B7BC4C433E0 for ; Fri, 15 May 2020 14:10:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9FD6E2054F for ; Fri, 15 May 2020 14:10:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726170AbgEOOKt (ORCPT ); Fri, 15 May 2020 10:10:49 -0400 Received: from mga14.intel.com ([192.55.52.115]:23237 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726140AbgEOOKt (ORCPT ); Fri, 15 May 2020 10:10:49 -0400 IronPort-SDR: Lvl0LWOKuTBWMprfi1yX22tZOyO0qrSB9ym2Q/OTsbcqKrj8+7rbdUtM9bcsdc0/MFu4U25FFW q8HtMsC4DO2w== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga001.fm.intel.com ([10.253.24.23]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 May 2020 07:10:49 -0700 IronPort-SDR: 54TbqBR7CXjYDsu+yd9jQlAkaAjG99wMxI2ia8etFYijKsxS7dIc+1yj3hatPR1kLCRXXsU3Hi WXtG+gio5/OQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,395,1583222400"; d="scan'208";a="372701841" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by fmsmga001.fm.intel.com with ESMTP; 15 May 2020 07:10:44 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jZb30-006sqV-VP; Fri, 15 May 2020 17:10:46 +0300 Date: Fri, 15 May 2020 17:10:46 +0300 From: Andy Shevchenko To: Serge Semin Cc: Thomas Bogendoerfer , Greg Kroah-Hartman , Jiri Slaby , Serge Semin , Alexey Malahov , Paul Burton , Ralf Baechle , Arnd Bergmann , Long Cheng , Maxime Ripard , Catalin Marinas , Will Deacon , Russell King , linux-mips@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, Heikki Krogerus , Kefeng Wang , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 4/4] serial: 8250_dw: Fix common clocks usage race condition Message-ID: <20200515141046.GF1634618@smile.fi.intel.com> References: <20200323024611.16039-1-Sergey.Semin@baikalelectronics.ru> <20200506233136.11842-1-Sergey.Semin@baikalelectronics.ru> <20200506233136.11842-5-Sergey.Semin@baikalelectronics.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200506233136.11842-5-Sergey.Semin@baikalelectronics.ru> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-serial-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On Thu, May 07, 2020 at 02:31:35AM +0300, Serge Semin wrote: > The race condition may happen if the UART reference clock is shared with > some other device (on Baikal-T1 SoC it's another DW UART port). In this > case if that device changes the clock rate while serial console is using > it the DW 8250 UART port might not only end up with an invalid uartclk > value saved, but may also experience a distorted output data since > baud-clock could have been changed. In order to fix this lets at least > try to adjust the 8250 port setting like UART clock rate in case if the > reference clock rate change is discovered. The driver will call the new > method to update 8250 UART port clock rate settings. It's done by means of > the clock event notifier registered at the port startup and unregistered > in the shutdown callback method. I'm wondering if clock framework itself can provide such a notifier? > Note 1. In order to avoid deadlocks we had to execute the UART port update > method in a dedicated deferred work. This is due to (in my opinion > redundant) the clock update implemented in the dw8250_set_termios() > method. So, and how you propose to update the clock when ->set_termios() is called? > Note 2. Before the ref clock is manually changed by the custom > set_termios() function we swap the port uartclk value with new rate > adjusted to be suitable for the requested baud. It is necessary in > order to effectively disable a functionality of the ref clock events > handler for the current UART port, since uartclk update will be done > a bit further in the generic serial8250_do_set_termios() function. ... > + struct notifier_block clk_notifier; > + struct work_struct clk_work; Oh, this seems too much. Perhaps, the compatible based quirk with your initial approach is much better for time being. -- With Best Regards, Andy Shevchenko