Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754836AbcDKSb3 (ORCPT ); Mon, 11 Apr 2016 14:31:29 -0400 Received: from www.linutronix.de ([62.245.132.108]:33191 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754509AbcDKSb1 (ORCPT ); Mon, 11 Apr 2016 14:31:27 -0400 Subject: Re: [PATCH] tty: serial: 8250_omap: do not defer termios changes To: Peter Hurley , John Ogness References: <8737r7ght7.fsf@linutronix.de> <570339E8.6010808@hurleysoftware.com> <87y48kftip.fsf@linutronix.de> <570BE48F.60801@hurleysoftware.com> Cc: Greg Kroah-Hartman , Tony Lindgren , nsekhar@ti.com, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, linux-omap@vger.kernel.org From: Sebastian Andrzej Siewior Message-ID: <570BED7B.9080803@linutronix.de> Date: Mon, 11 Apr 2016 20:31:23 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.7.0 MIME-Version: 1.0 In-Reply-To: <570BE48F.60801@hurleysoftware.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1248 Lines: 33 On 04/11/2016 07:53 PM, Peter Hurley wrote: > On 04/11/2016 01:18 AM, John Ogness wrote: >> On 2016-04-05, Peter Hurley wrote: >>> On 03/31/2016 01:41 AM, John Ogness wrote: >>>> It has been observed that the TX-DMA can stall >>> >>> Does this happen on any other OMAP part besides am335x? >>> I looked back over the LKML history of this and didn't see >>> any other design implicated in this problem. >> >> I just ran the tests again using 4.6-rc2. I am able to reproduce the >> dma-tx stall with am335x/edma and dra7/sdma. > > I thought we already established sdma was not to be used since > the hardware does not actually support pausing without data loss. This workaround was not invented for sdma but for edma (with am335x). > http://www.spinics.net/lists/linux-serial/msg18503.html This could be fixed. See http://www.spinics.net/lists/linux-serial/msg18517.html http://www.spinics.net/lists/linux-serial/msg18531.html rmk was fine with it from what I read. So what is missing is just refurbish the patch (update the comment according to rmk replay) and then we could re-enable DMA again. > So I'm wondering if we're carrying all this extra DMA complexity > and workarounds for just am335x? > Sebastian