From patchwork Tue May 24 12:04:17 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Vinod Koul X-Patchwork-Id: 811732 Received: from bombadil.infradead.org (bombadil.infradead.org [18.85.46.34]) by demeter2.kernel.org (8.14.4/8.14.3) with ESMTP id p4OCdvfD015634 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Tue, 24 May 2011 12:40:20 GMT Received: from canuck.infradead.org ([2001:4978:20e::1]) by bombadil.infradead.org with esmtps (Exim 4.76 #1 (Red Hat Linux)) id 1QOqsO-0005YL-EO; Tue, 24 May 2011 12:38:20 +0000 Received: from localhost ([127.0.0.1] helo=canuck.infradead.org) by canuck.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1QOqsM-0007jK-S0; Tue, 24 May 2011 12:38:18 +0000 Received: from mga14.intel.com ([143.182.124.37]) by canuck.infradead.org with esmtp (Exim 4.76 #1 (Red Hat Linux)) id 1QOqsJ-0007j1-Pn for linux-arm-kernel@lists.infradead.org; Tue, 24 May 2011 12:38:16 +0000 Received: from azsmga001.ch.intel.com ([10.2.17.19]) by azsmga102.ch.intel.com with ESMTP; 24 May 2011 05:38:13 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.65,261,1304319600"; d="scan'208";a="575301" Received: from vkoul-udesk3.iind.intel.com (HELO localhost.localdomain) ([10.223.85.69]) by azsmga001.ch.intel.com with ESMTP; 24 May 2011 05:38:11 -0700 From: "Koul, Vinod" To: LKML Subject: [PATCH] dmaengine: Add API documentation for slave dma usage Date: Tue, 24 May 2011 17:34:17 +0530 Message-Id: <1306238657-30089-1-git-send-email-vinod.koul@intel.com> X-Mailer: git-send-email 1.7.0.4 X-CRM114-Version: 20090807-BlameThorstenAndJenny ( TRE 0.7.6 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20110524_083815_997890_4B998322 X-CRM114-Status: GOOD ( 18.81 ) X-Spam-Score: -2.3 (--) X-Spam-Report: SpamAssassin version 3.3.1 on canuck.infradead.org summary: Content analysis details: (-2.3 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -2.3 RCVD_IN_DNSWL_MED RBL: Sender listed at http://www.dnswl.org/, medium trust [143.182.124.37 listed in list.dnswl.org] Cc: Vinod Koul , Linus Walleij , Russell King , Dan , linux-arm-kernel@lists.infradead.org X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Sender: linux-arm-kernel-bounces@lists.infradead.org Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Greylist: IP, sender and recipient auto-whitelisted, not delayed by milter-greylist-4.2.6 (demeter2.kernel.org [140.211.167.43]); Tue, 24 May 2011 12:40:20 +0000 (UTC) From: Vinod Koul Signed-off-by: Vinod Koul --- Documentation/dma-slave-api.txt | 74 +++++++++++++++++++++++++++++++++++++++ 1 files changed, 74 insertions(+), 0 deletions(-) create mode 100644 Documentation/dma-slave-api.txt diff --git a/Documentation/dma-slave-api.txt b/Documentation/dma-slave-api.txt new file mode 100644 index 0000000..7498807 --- /dev/null +++ b/Documentation/dma-slave-api.txt @@ -0,0 +1,74 @@ + Slave DMA API Guide + =================== + + Vinod Koul + +This is a guide to device driver writers on how to use the Slave-DMA API of the +DMA Engine. This is applicable only for slave DMA usage and not async tx. For +the async tx usage of DMA Engine please see +Documentation/crypto/async-tx-api.txt + +The slave DMA usage consists of following steps +1. Allocate a DMA slave channel +2. Set slave and controller specific parameters +3. Get a descriptor for transaction +4. Submit the transaction and wait for callback notification + +1. Allocate a DMA slave channel +Channel allocation is slightly different in the slave DMA context, client +drivers typically need a channel from a particular DMA controller only and even +in some cases a specific channel is desired. To request a channel +__dma_request_channel() API is used. + +Interface: +struct dma_chan *dma_request_channel(dma_cap_mask_t mask, + dma_filter_fn filter_fn, + void *filter_param); +where dma_filter_fn is defined as: +typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param); + +When the optional 'filter_fn' parameter is set to NULL dma_request_channel +simply returns the first channel that satisfies the capability mask. Otherwise, +when the mask parameter is insufficient for specifying the necessary channel, +the filter_fn routine can be used to disposition the available channels in the +system. The filter_fn routine is called once for each free channel in the +system. Upon seeing a suitable channel filter_fn returns DMA_ACK which flags +that channel to be the return value from dma_request_channel. A channel +allocated via this interface is exclusive to the caller, until +dma_release_channel() is called. + +2. Set slave and controller specific parameters +Next step is always to pass some specific information to the DMA driver. Most of +the generic information which a slave DMA can use is in struct dma_slave_config. +It allows the clients to specify DMA direction, DMA addresses, bus widths, DMA +burst lengths etc. If some DMA controllers have more parameters to be sent then +they should try to embed struct dma_slave_config in their controller specific +structure. That gives flexibility to client to pass more parameters, if +required. + +Interface: +struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_sg)( + struct dma_chan *chan, + struct scatterlist *dst_sg, unsigned int dst_nents, + struct scatterlist *src_sg, unsigned int src_nents, + unsigned long flags); +struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)( + struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len, + size_t period_len, enum dma_data_direction direction); + +4. Submit the transaction(s) and wait for callback notification when slave API +is 3 above returns, the non NULL value would imply a "descriptor" for the +transaction. These transaction(s) would need to be submitted which pushes them +into queue in DMA driver. If DMA is idle then the first descriptor submit will +be pushed to DMA and subsequent ones will be queued. On completion of the DMA +operation the next in queue is submitted and a tasklet triggered. The tasklet +would then call the client driver completion callback routine for notification, +if set. + +Additional usage notes +1/ Although DMA engine specifies that completion callback routines cannot submit +any new operations, but typically for slave DMA subsequent transaction may not +be available for submit prior to callback routine being called. This requirement +|is not a requirement for DMA-slave devices. But they should take care to drop +the spin-lock they might be holding before calling the callback routine +