From patchwork Mon Oct 1 10:00:35 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Ike Panhc X-Patchwork-Id: 188252 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from chlorine.canonical.com (chlorine.canonical.com [91.189.94.204]) by ozlabs.org (Postfix) with ESMTP id 4EA8C2C00B7 for ; Mon, 1 Oct 2012 20:00:51 +1000 (EST) Received: from localhost ([127.0.0.1] helo=chlorine.canonical.com) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1TIcl3-0006hi-Io; Mon, 01 Oct 2012 09:57:49 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by chlorine.canonical.com with esmtp (Exim 4.71) (envelope-from ) id 1TIcl1-0006hU-Oo for kernel-team@lists.ubuntu.com; Mon, 01 Oct 2012 09:57:47 +0000 Received: from 220-134-16-35.hinet-ip.hinet.net ([220.134.16.35] helo=canonical.com) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1TIcnp-0003JO-V2 for kernel-team@lists.ubuntu.com; Mon, 01 Oct 2012 10:00:42 +0000 From: Ike Panhc To: kernel-team@lists.ubuntu.com Subject: [PATCH 02/19] common: DMA-mapping: add DMA_ATTR_SKIP_CPU_SYNC attribute Date: Mon, 1 Oct 2012 18:00:35 +0800 Message-Id: <1349085635-23141-1-git-send-email-ike.pan@canonical.com> X-Mailer: git-send-email 1.7.9.5 In-Reply-To: <1349085560-23019-1-git-send-email-ike.pan@canonical.com> References: <1349085560-23019-1-git-send-email-ike.pan@canonical.com> X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.13 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: kernel-team-bounces@lists.ubuntu.com Errors-To: kernel-team-bounces@lists.ubuntu.com From: Marek Szyprowski BugLink: http://launchpad.net/bugs/1059432 This patch adds DMA_ATTR_SKIP_CPU_SYNC attribute to the DMA-mapping subsystem. By default dma_map_{single,page,sg} functions family transfer a given buffer from CPU domain to device domain. Some advanced use cases might require sharing a buffer between more than one device. This requires having a mapping created separately for each device and is usually performed by calling dma_map_{single,page,sg} function more than once for the given buffer with device pointer to each device taking part in the buffer sharing. The first call transfers a buffer from 'CPU' domain to 'device' domain, what synchronizes CPU caches for the given region (usually it means that the cache has been flushed or invalidated depending on the dma direction). However, next calls to dma_map_{single,page,sg}() for other devices will perform exactly the same sychronization operation on the CPU cache. CPU cache sychronization might be a time consuming operation, especially if the buffers are large, so it is highly recommended to avoid it if possible. DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of the CPU cache for the given buffer assuming that it has been already transferred to 'device' domain. This attribute can be also used for dma_unmap_{single,page,sg} functions family to force buffer to stay in device domain after releasing a mapping for it. Use this attribute with care! Signed-off-by: Marek Szyprowski Reviewed-by: Kyungmin Park (Upstream commit bdf5e4871f1b41150236e2337837399109469e65) Signed-off-by: Ike Panhc --- Documentation/DMA-attributes.txt | 24 ++++++++++++++++++++++++ include/linux/dma-attrs.h | 1 + 2 files changed, 25 insertions(+) diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index 725580d..f503090 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -67,3 +67,27 @@ set on each call. Since it is optional for platforms to implement DMA_ATTR_NO_KERNEL_MAPPING, those that do not will simply ignore the attribute and exhibit default behavior. + +DMA_ATTR_SKIP_CPU_SYNC +---------------------- + +By default dma_map_{single,page,sg} functions family transfer a given +buffer from CPU domain to device domain. Some advanced use cases might +require sharing a buffer between more than one device. This requires +having a mapping created separately for each device and is usually +performed by calling dma_map_{single,page,sg} function more than once +for the given buffer with device pointer to each device taking part in +the buffer sharing. The first call transfers a buffer from 'CPU' domain +to 'device' domain, what synchronizes CPU caches for the given region +(usually it means that the cache has been flushed or invalidated +depending on the dma direction). However, next calls to +dma_map_{single,page,sg}() for other devices will perform exactly the +same sychronization operation on the CPU cache. CPU cache sychronization +might be a time consuming operation, especially if the buffers are +large, so it is highly recommended to avoid it if possible. +DMA_ATTR_SKIP_CPU_SYNC allows platform code to skip synchronization of +the CPU cache for the given buffer assuming that it has been already +transferred to 'device' domain. This attribute can be also used for +dma_unmap_{single,page,sg} functions family to force buffer to stay in +device domain after releasing a mapping for it. Use this attribute with +care! diff --git a/include/linux/dma-attrs.h b/include/linux/dma-attrs.h index a37c10c..f83f793 100644 --- a/include/linux/dma-attrs.h +++ b/include/linux/dma-attrs.h @@ -16,6 +16,7 @@ enum dma_attr { DMA_ATTR_WRITE_COMBINE, DMA_ATTR_NON_CONSISTENT, DMA_ATTR_NO_KERNEL_MAPPING, + DMA_ATTR_SKIP_CPU_SYNC, DMA_ATTR_MAX, };