Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760893AbXI1BOS (ORCPT ); Thu, 27 Sep 2007 21:14:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759816AbXI1BOE (ORCPT ); Thu, 27 Sep 2007 21:14:04 -0400 Received: from netops-testserver-3-out.sgi.com ([192.48.171.28]:57390 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758435AbXI1BOC (ORCPT ); Thu, 27 Sep 2007 21:14:02 -0400 From: akepner@sgi.com Date: Thu, 27 Sep 2007 18:13:02 -0700 To: Grant Grundler , Jesse Barnes , Jes Sorensen , Randy Dunlap , RolandDreier , James Bottomley Cc: linux-kernel@vger.kernel.org Subject: [3/4] dma: document dma_flags_set_dmabarrier() Message-ID: <20070928011302.GP30013@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1832 Lines: 48 Document dma_flags_set_dmabarrier(). Signed-off-by: Arthur Kepner --- DMA-API.txt | 26 ++++++++++++++++++++++++++ 1 files changed, 26 insertions(+) diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index cc7a8c3..5fc0bba 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -544,3 +544,29 @@ size is the size (and should be a page-sized multiple). The return value will be either a pointer to the processor virtual address of the memory, or an error (via PTR_ERR()) if any part of the region is occupied. + +int +dma_flags_set_dmabarrier(int dir) + +Amend dir (one of the enum dma_data_direction values), with a +platform-specific "dmabarrier" attribute. The dmabarrier attribute +forces a flush of all in-flight DMA when the associated memory +region is written to (see example below.) + +This provides a mechanism to enforce ordering of DMA on platforms that +permit DMA to be reordered between device and host memory (within a +NUMA interconnect). On other platforms this is a nop. + +The dmabarrier would be set when the memory region is mapped for DMA, +e.g.: + + int count, flags = dma_flags_set_dmabarrier(DMA_BIDIRECTIONAL); + .... + count = dma_map_sg(dev, sglist, nents, flags); + +As an example of a situation where this would be useful, suppose that +the device does a DMA write to indicate that data is ready and +available in memory. The DMA of the "completion indication" could +race with data DMA. Using a dmabarrier on the memory used for +completion indications would prevent the race. + - 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/