From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752379Ab2AaGk3 (ORCPT ); Tue, 31 Jan 2012 01:40:29 -0500 Received: from mga11.intel.com ([192.55.52.93]:49171 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751646Ab2AaGk1 (ORCPT ); Tue, 31 Jan 2012 01:40:27 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="118405049" Subject: Re: [PATCH 1/7 v2] dmaengine: add a simple dma library From: Vinod Koul To: Guennadi Liakhovetski Cc: linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, Magnus Damm , Yoshihiro Shimoda , linux-mmc@vger.kernel.org, alsa-devel@alsa-project.org, linux-serial@vger.kernel.org, Paul Mundt In-Reply-To: References: <1327589784-4287-1-git-send-email-g.liakhovetski@gmx.de> <1327589784-4287-2-git-send-email-g.liakhovetski@gmx.de> <1327912346.1527.13.camel@vkoul-udesk3> Content-Type: text/plain; charset="UTF-8" Date: Tue, 31 Jan 2012 12:11:30 +0530 Message-ID: <1327992090.1527.116.camel@vkoul-udesk3> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2012-01-30 at 10:34 +0100, Guennadi Liakhovetski wrote: > > I don't still comprehend the need for a library on top of dmaengine > > which gain is just a library between clients and dmacs. Surely we don't > > want to write another abstraction on top of one provided? > > > > If the question is to handle scatter-gather even if the hardware doesn't > > have the capability, then why don't add that in dmaengine itself rather > > than one more layer? > > Well, yes, adding new abstraction layers is always a decision, that has to > be well justified. In this case it does at least make the life easier for > two sh-mobile drivers: shdma and the new SUDMAC driver. > > However, I did name the library in a generic way without reference to sh, > assuming, that it might with time become useful for other architectures > too. The reasons why I prefered to keep it as an optional addition to > dmaengine core, instead of tightly integrating it with it are, that (1) I > did not want to add useless code to drivers, that do not need it, So are we sure that only sh-mobile drivers need this capablity? Btw does you hardware only support single transfers and no sg support, would this remain the same in future? > (2) I am > not sure if and when this library will become useful for other drivers: > apart from sh I am only familiar with one more dmaengine driver: > ipu/ipu_idmac.c, and that one supports scatter-gather lists in a limited > way and has some further peculiarities, that would likely make it a bad > match for the simple DMA library, typically the dmacs will support this in some form or other, so your point is valid :) > (3) keeping it separate makes its > further development easier. > > OTOH, I'm certainly fine with a tighter library integration with the > dmaengine core. I think, it still would be better to keep it in a separate > file and only build it if needed, right? This woult also simplify code > debugging and further development. I can remove the "simple" notation, > which does make it look like an additional abstraction layer, and replace > it with, say, sgsoft (scatter-gather software implementation)? that would be more apt :) > A more > interesting question is what to do with struct dma_simple_dev, struct > dma_simple_chan, struct dma_simple_desc, that embed struct dma_device, > struct dma_chan and struct dma_async_tx_descriptor respectively. I don't > think we want to merge all the additions from those wrapping structs back > into their dmaengine counterparts? Sure they should be kept separate. I like the wrapping, this keeps it simple. > > How would you like to do this? Don't you think, it would be good to allow > both: either implement a dmaengine driver directly, exactly as all drivers > are doing now, or use the additional helper library for suitable (simple) > hardware types? I see it similar to I2C, where you either implement an I2C > driver directly, or you use the bitbanging abstraction for simpler > hardware. I think it would be good to have both, this can be used by folks who don't have sg support available. -- ~Vinod