Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754825AbYDABhe (ORCPT ); Mon, 31 Mar 2008 21:37:34 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752126AbYDABh0 (ORCPT ); Mon, 31 Mar 2008 21:37:26 -0400 Received: from relay2.sgi.com ([192.48.171.30]:59727 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752101AbYDABh0 (ORCPT ); Mon, 31 Mar 2008 21:37:26 -0400 From: akepner@sgi.com Date: Mon, 31 Mar 2008 18:35:58 -0700 To: Andrew Morton Cc: Tony Luck , Jesse Barnes , Jes Sorensen , Randy Dunlap , Roland Dreier , James Bottomley , David Miller , Benjamin Herrenschmidt , Grant Grundler , Michael Ellerman , linux-kernel@vger.kernel.org Subject: [PATCH 1/3 v6] dma: document dma_*map*_attrs() interfaces Message-ID: <20080401013558.GC29410@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 List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4216 Lines: 121 Document the new dma_*map*_attrs() functions. Signed-off-by: Arthur Kepner --- DMA-API.txt | 65 +++++++++++++++++++++++++++++++++++++++++++++++++++++ DMA-attributes.txt | 24 +++++++++++++++++++ 2 files changed, 89 insertions(+) diff --git a/Documentation/DMA-API.txt b/Documentation/DMA-API.txt index b939ebb..fdb82b0 100644 --- a/Documentation/DMA-API.txt +++ b/Documentation/DMA-API.txt @@ -395,6 +395,71 @@ Notes: You must do this: See also dma_map_single(). +dma_addr_t +dma_map_single_attrs(struct device *dev, void *cpu_addr, size_t size, + enum dma_data_direction dir, + struct dma_attrs *attrs) + +void +dma_unmap_single_attrs(struct device *dev, dma_addr_t dma_addr, + size_t size, enum dma_data_direction dir, + struct dma_attrs *attrs) + +int +dma_map_sg_attrs(struct device *dev, struct scatterlist *sgl, + int nents, enum dma_data_direction dir, + struct dma_attrs *attrs) + +void +dma_unmap_sg_attrs(struct device *dev, struct scatterlist *sgl, + int nents, enum dma_data_direction dir, + struct dma_attrs *attrs) + +The four functions above are just like the counterpart functions +without the _attrs suffixes, except that they pass an optional +struct dma_attrs*. + +struct dma_attrs encapsulates a set of "dma attributes". For the +definition of struct dma_attrs see linux/dma-attrs.h. + +The interpretation of dma attributes is architecture-specific, and +each attribute should be documented in Documentation/DMA-attributes.txt. + +If struct dma_attrs* is NULL, the semantics of each of these +functions is identical to those of the corresponding function +without the _attrs suffix. As a result dma_map_single_attrs() +can generally replace dma_map_single(), etc. + +As an example of the use of the *_attrs functions, here's how +you could pass an attribute DMA_ATTR_FOO when mapping memory +for DMA: + +#include +/* DMA_ATTR_FOO should be defined in linux/dma-attrs.h and + * documented in Documentation/DMA-attributes.txt */ +... + + DECLARE_DMA_ATTRS(attrs); + dma_set_attr(&attrs, DMA_ATTR_FOO); + .... + n = dma_map_sg_attrs(dev, sg, nents, DMA_TO_DEVICE, &attr); + .... + +Architectures that care about DMA_ATTR_FOO would check for its +presence in their implementations of the mapping and unmapping +routines, e.g.: + +void whizco_dma_map_sg_attrs(struct device *dev, dma_addr_t dma_addr, + size_t size, enum dma_data_direction dir, + struct dma_attrs *attrs) +{ + .... + int foo = dma_get_attr(attrs, DMA_ATTR_FOO); + .... + if (foo) + /* twizzle the frobnozzle */ + .... + Part II - Advanced dma_ usage ----------------------------- diff --git a/Documentation/DMA-attributes.txt b/Documentation/DMA-attributes.txt index e69de29..6d772f8 100644 --- a/Documentation/DMA-attributes.txt +++ b/Documentation/DMA-attributes.txt @@ -0,0 +1,24 @@ + DMA attributes + ============== + +This document describes the semantics of the DMA attributes that are +defined in linux/dma-attrs.h. + +DMA_ATTR_WRITE_BARRIER +---------------------- + +DMA_ATTR_WRITE_BARRIER is a (write) barrier attribute for DMA. DMA +to a memory region with the DMA_ATTR_WRITE_BARRIER attribute forces +all pending DMA writes to complete, and thus provides a mechanism to +strictly order DMA from a device across all intervening busses and +bridges. This barrier is not specific to a particular type of +interconnect, it applies to the system as a whole, and so its +implementation must account for the idiosyncracies of the system all +the way from the DMA device to memory. + +As an example of a situation where DMA_ATTR_WRITE_BARRIER would be +useful, suppose that a 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. Mapping the memory used for completion +indications with DMA_ATTR_WRITE_BARRIER 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/