From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755018AbcAWVYh (ORCPT ); Sat, 23 Jan 2016 16:24:37 -0500 Received: from mail-pf0-f176.google.com ([209.85.192.176]:36164 "EHLO mail-pf0-f176.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754760AbcAWVYd (ORCPT ); Sat, 23 Jan 2016 16:24:33 -0500 Subject: Re: [PATCH 3/4] tty: serial: 8250: omap: convert to using cyclic transfers To: Sebastian Andrzej Siewior , John Ogness , gregkh@linuxfoundation.org, vinod.koul@intel.com References: <87zivxq57d.fsf@linutronix.de> <56A25959.4060802@hurleysoftware.com> <56A3DF17.2070908@linutronix.de> Cc: dan.j.williams@intel.com, tony@atomide.com, nsekhar@ti.com, peter.ujfalusi@ti.com, dmaengine@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org From: Peter Hurley Message-ID: <56A3EF8E.6020204@hurleysoftware.com> Date: Sat, 23 Jan 2016 13:24:30 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <56A3DF17.2070908@linutronix.de> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/23/2016 12:14 PM, Sebastian Andrzej Siewior wrote: > On 01/22/2016 05:31 PM, Peter Hurley wrote: >> Hi John, >> >> On 01/22/2016 02:27 AM, John Ogness wrote: >>> Note that an ugly device-tree lookup hack is implemented in order >>> to detect if the sDMA engine is being used. This is necessary >>> because the sDMA driver does not implement pause/resume correctly >>> and therefore requires slightly different logic for the UART >>> driver. >> >> No, this is not acceptable. >> >> Please work with Vinod to refine the dma_get_slave_caps() interface >> so that dmaengine drivers that don't provide the _documented_ pause/resume >> support can be identified generically. > > But we could implement the pause/resume bits correctly wait until it is > merge and post this and rely on the fact that it works (including error > checking). RMK requested that he wants the UART driver fixed before > touching the DMA driver and this has been done in meantime. So we could > go ahead and add the missing pieces to SDMA. There is zero chance of backporting this. Let's move forward and fix the problem. At a minimum, the reason this code needs to know which DMA slave driver is because the sDMA driver lies about pause support. Rather than continuing to hide this broken behavior behind the dmaengine API, expose a method of generically determining what the slave driver actually does. It's the only sane choice. Regards, Peter Hurley FWIW, I'm not convinced about cyclic transfers. But doing a complete review of that is a bit off.