Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932288AbVJCPkX (ORCPT ); Mon, 3 Oct 2005 11:40:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932299AbVJCPkX (ORCPT ); Mon, 3 Oct 2005 11:40:23 -0400 Received: from ylpvm12-ext.prodigy.net ([207.115.57.43]:30409 "EHLO ylpvm12.prodigy.net") by vger.kernel.org with ESMTP id S932288AbVJCPkX (ORCPT ); Mon, 3 Oct 2005 11:40:23 -0400 X-ORBL: [69.107.75.50] Date: Mon, 03 Oct 2005 08:40:19 -0700 From: David Brownell To: rmk+lkml@arm.linux.org.uk Subject: Re: [RFC][PATCH] SPI subsystem Cc: linux-kernel@vger.kernel.org, basicmark@yahoo.com, arjan@infradead.org References: <20051003105748.213.qmail@web33014.mail.mud.yahoo.com> <1128337656.17024.10.camel@laptopd505.fenrus.org> <20051003151457.AD64FEE8CE@adsl-69-107-32-110.dsl.pltn13.pacbell.net> <20051003152312.GH16717@flint.arm.linux.org.uk> In-Reply-To: <20051003152312.GH16717@flint.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-Id: <20051003154019.02A66EE8CF@adsl-69-107-32-110.dsl.pltn13.pacbell.net> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 851 Lines: 19 > I believe the issue is that you can't properly control the alignment > to ensure that you don't inadvertantly dirty the cache lines > corresponding with the memory you're performing DMA to/from. That's a much better (== content-ful) explanation; thanks Russell. Cache line sharing can indeed be a PITA ... and while it's an issue that's not unique to DMA from the stack, it's something that's less manageable there. Plus, DMA isn't always cache-coherent. Meaning that for example DMA to the stack might bypass the cache and then later be overwritten by flushing cached stack updates. (etc.) - Dave - 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/