Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751097AbZKCJ6w (ORCPT ); Tue, 3 Nov 2009 04:58:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1750796AbZKCJ6v (ORCPT ); Tue, 3 Nov 2009 04:58:51 -0500 Received: from bar.sig21.net ([80.81.252.164]:60325 "EHLO bar.sig21.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750710AbZKCJ6v (ORCPT ); Tue, 3 Nov 2009 04:58:51 -0500 Date: Tue, 3 Nov 2009 11:00:18 +0100 From: Johannes Stezenbach To: Artem Bityutskiy Cc: David Woodhouse , David Brownell , linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mtd: m25p80: make command buffer DMA-safe Message-ID: <20091103100018.GA20519@sig21.net> References: <20091028132137.GA17813@sig21.net> <1257230165.21596.33.camel@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1257230165.21596.33.camel@localhost> User-Agent: Mutt/1.5.20 (2009-06-14) X-Spam-21-Score: -3.6 (---) X-Spam-21-Report: No, score=-3.6 required=5.0 tests=ALL_TRUSTED=-1.8,AWL=0.817,BAYES_00=-2.599 autolearn=no Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1054 Lines: 23 On Tue, Nov 03, 2009 at 08:36:05AM +0200, Artem Bityutskiy wrote: > On Wed, 2009-10-28 at 14:21 +0100, Johannes Stezenbach wrote: > > spi_write() requires the buffer to be DMA-safe, kmalloc() > > it seperately to ensure this. > > Even though it is just 4 or 5 bytes it can do DMA? Does not sound too > sane to use DMA in that case. Does this patch fix a real error? > > I do not know much about SPI, but for me it sounds like there should be > a method to ask SPI to avoid using DMA, and you should use that method. It fixes a real error -- with an out-of-tree driver and ancient kernel. For the flash read/write case it is used with list-DMA (e.g. write 4 bytes, read 64KB). There are extensive comments in include/linux/spi/spi.h which document the DMA-safe requirement of the buffers. Thanks Johannes -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/