From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758616AbcDHPw2 (ORCPT ); Fri, 8 Apr 2016 11:52:28 -0400 Received: from www381.your-server.de ([78.46.137.84]:38338 "EHLO www381.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758543AbcDHPw0 (ORCPT ); Fri, 8 Apr 2016 11:52:26 -0400 Subject: Re: [alsa-devel] [PATCH 5/5 v4] ASoC: dwc: Update DOCUMENTATION for I2S Driver To: Jose Abreu , Mark Brown References: <20160407175326.GX1924@sirena.org.uk> <570782BF.10402@synopsys.com> Cc: alsa-devel@alsa-project.org, lgirdwood@gmail.com, airlied@linux.ie, Vineet.Gupta1@synopsys.com, Alexey.Brodkin@synopsys.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, CARLOS.PALMINHA@synopsys.com, tiwai@suse.com, linux-snps-arc@lists.infradead.org, architt@codeaurora.org From: Lars-Peter Clausen Message-ID: <5707D3AD.8030308@metafoo.de> Date: Fri, 8 Apr 2016 17:52:13 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.6.0 MIME-Version: 1.0 In-Reply-To: <570782BF.10402@synopsys.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Authenticated-Sender: lars@metafoo.de Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/08/2016 12:06 PM, Jose Abreu wrote: > Hi Mark, > > > On 07-04-2016 18:53, Mark Brown wrote: >> On Thu, Apr 07, 2016 at 05:53:59PM +0100, Jose Abreu wrote: >> >>> + Optional properties: >>> + - snps,use-dmaengine: If set the driver will use ALSA DMA engine. If set >>> + it is required to use the properties 'dmas' and 'dma-names'. >> This is not a good interface, it's describing Linux internal APIs. If >> the device needs to operate in PIO mode it should just do that. > > I added this interface because there is no direct way to check if DMA is > available on the I2S controller so it is not possible to automatically change > between DMA and PIO mode. As the I2S controller can be built with or without DMA > support it is necessary to somehow check if DMA is enabled or not and according > to that use either ALSA DMA engine or the custom platform driver sent in these > patches. I did not want to remove drivers functionality so I added this property > to the DT. This way a user can select between DMA and PIO mode. That's OK, but you need to describe the hardware, not the indented behavior of the software driver.