From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760727Ab3GaUBu (ORCPT ); Wed, 31 Jul 2013 16:01:50 -0400 Received: from caramon.arm.linux.org.uk ([78.32.30.218]:39441 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754297Ab3GaUBt (ORCPT ); Wed, 31 Jul 2013 16:01:49 -0400 Date: Wed, 31 Jul 2013 21:01:35 +0100 From: Russell King - ARM Linux To: Stefano Stabellini Cc: xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, konrad.wilk@oracle.com, Ian.Campbell@citrix.com, will.deacon@arm.com Subject: Re: [PATCH v2 RFC 2/8] arm: introduce a global dma_ops pointer Message-ID: <20130731200135.GZ24642@n2100.arm.linux.org.uk> References: <1375300452-12545-2-git-send-email-stefano.stabellini@eu.citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1375300452-12545-2-git-send-email-stefano.stabellini@eu.citrix.com> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 31, 2013 at 08:54:06PM +0100, Stefano Stabellini wrote: > Initially set dma_ops to arm_dma_ops. > Use dma_ops instead of arm_dma_ops in dmabounce. > > Signed-off-by: Stefano Stabellini > CC: will.deacon@arm.com > CC: linux@arm.linux.org.uk If you're using swiotlb, there's little point in converting dmabounce to be able to use it, because it's basically providing the same functionality - dmabounce is there to do software buffer bouncing within the DMA to move streaming buffers from DMA-inaccessible memory into DMA-accessible memory. It's original use is with older SoCs with buggy DMA (eg, those which can only address alternate 1MB chunks of memory for example) but also got used in situations where alternative solutions would've been better (like using swiotlb.) I've been discouraging its use as it's suffered from memory exhaustion problems (there's a number of threads and bug reports which were never solved about IXP4xx(?) platforms suffering this due to this bouncing.)