From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751201AbcFBEm3 (ORCPT ); Thu, 2 Jun 2016 00:42:29 -0400 Received: from plaes.org ([188.166.43.21]:37533 "EHLO plaes.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750754AbcFBEm2 convert rfc822-to-8bit (ORCPT ); Thu, 2 Jun 2016 00:42:28 -0400 Message-ID: <1464842546.23881.3.camel@plaes.org> Subject: Re: [linux-sunxi] Re: [PATCH 5/5] RFC spi: sun4i: add DMA support From: Priit Laes To: maxime.ripard@free-electrons.com, Mark Brown Cc: Michal Suchanek , Geert Uytterhoeven , linux-sunxi , Chen-Yu Tsai , linux-spi , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Date: Thu, 02 Jun 2016 07:42:26 +0300 In-Reply-To: <20160601180056.GA4908@lukather> References: <20160530112610.GJ29837@sirena.org.uk> <20160530150343.GL29837@sirena.org.uk> <20160530155016.GO29837@sirena.org.uk> <20160601180056.GA4908@lukather> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.18.5.2-0ubuntu1 Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2016-06-01 at 20:00 +0200, Maxime Ripard wrote: > Hi, > > On Mon, May 30, 2016 at 04:50:16PM +0100, Mark Brown wrote: > > > > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote: > > > > > > On 30 May 2016 at 17:03, Mark Brown wrote: > > > > > > > > > > > I really don't think it's worth caring too much about cases > > > > where the > > > > DMA driver hasn't been compiled in, it's not like SPI is the > > > > only thing > > > > > > It's what the driver did to start with and it was requested to > > > fall > > > back to non-DMA in the case DMA is not available. > > Why?  I really can't see any sensible use case for this that > > doesn't > > have a better solution available. > SPI works just fine without DMA, which might just be considered an > (optional) optimisation. > > We've been using it without DMA for years now, and it was working > just > fine, and it will work even better with the other patches in this > serie. There's no reason to add a hard dependency on something that > we > don't really need. > Actually it non-DMA case works fine if you don't need SPI transfers larger than SUN4I_FIFO_DEPTH - 1, which is 63 bytes. This was addressed by this patch, but was never applied: http://permalink.gmane.org/gmane.linux.kernel.spi.devel/18950