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=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 722C0C433B4 for ; Wed, 21 Apr 2021 10:11:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42EF761449 for ; Wed, 21 Apr 2021 10:11:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238311AbhDUKMb (ORCPT ); Wed, 21 Apr 2021 06:12:31 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56768 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235189AbhDUKMa (ORCPT ); Wed, 21 Apr 2021 06:12:30 -0400 X-Greylist: delayed 494 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Wed, 21 Apr 2021 03:11:57 PDT Received: from sym2.noone.org (sym2.noone.org [IPv6:2a01:4f8:120:4161::3]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 15D4CC06174A; Wed, 21 Apr 2021 03:11:57 -0700 (PDT) Received: by sym2.noone.org (Postfix, from userid 1002) id 4FQGNT1gRhzvjfp; Wed, 21 Apr 2021 12:03:53 +0200 (CEST) Date: Wed, 21 Apr 2021 12:03:52 +0200 From: Tobias Klauser To: Johan Hovold Cc: Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 02/26] serial: altera_jtaguart: drop low-latency workaround Message-ID: <20210421100352.vayt5himhl7php4h@distanz.ch> References: <20210421095509.3024-1-johan@kernel.org> <20210421095509.3024-3-johan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210421095509.3024-3-johan@kernel.org> User-Agent: NeoMutt/20170113 (1.7.2) Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org On 2021-04-21 at 11:54:45 +0200, Johan Hovold wrote: > Commit 53dd0ba7a6f4 ("tty: serial: altera_jtag: drop uart_port->lock > before calling tty_flip_buffer_push()") claimed to address a locking > issue but only provided a dubious lockdep splat from an unrelated > driver, which in the end turned out to be due a broken local change > carried by the author. > > Unfortunately these patches were merged before the issue had been > analysed properly so the commit messages makes no sense whatsoever. > > The real issue was first seen on RT which at the time effectively always > set the low_latency flag for all serial drivers by patching > tty_flip_buffer_push(). This in turn revealed that many drivers did not > handle the infamous low_latency behaviour which meant that data was > pushed immediately to the line discipline instead of being deferred to a > work queue. > > Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"), > tty_flip_buffer_push() always schedules a work item to push data to the > line discipline and there's no need to keep any low_latency hacks > around. > > Link: https://lore.kernel.org/linux-serial/cover.1376923198.git.viresh.kumar@linaro.org/ > Cc: Tobias Klauser > Signed-off-by: Johan Hovold Acked-by: Tobias Klauser Thanks