Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757017Ab1EYHrd (ORCPT ); Wed, 25 May 2011 03:47:33 -0400 Received: from mail-iw0-f174.google.com ([209.85.214.174]:39514 "EHLO mail-iw0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756233Ab1EYHrc convert rfc822-to-8bit (ORCPT ); Wed, 25 May 2011 03:47:32 -0400 MIME-Version: 1.0 In-Reply-To: References: <1306238657-30089-1-git-send-email-vinod.koul@intel.com> <1306253171.30236.9.camel@vkoul-udesk3> Date: Wed, 25 May 2011 09:47:31 +0200 Message-ID: Subject: Re: [PATCH] dmaengine: Add API documentation for slave dma usage From: Per Forlin To: Dan Williams Cc: "Koul, Vinod" , Linus Walleij , Russell King , LKML , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3011 Lines: 57 On 24 May 2011 23:03, Dan Williams wrote: > On Tue, May 24, 2011 at 9:06 AM, Koul, Vinod wrote: >> On Tue, 2011-05-24 at 17:40 +0200, Per Forlin wrote: >>> Hi Vinod, >>> >>> On Tue, May 24, 2011 at 2:04 PM, Koul, Vinod wrote: >>> > 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 >>> I suggest putting this in subsection of dmaengine.txt instead. >>> dmaengine.txt would be the natural place to look at. >> Agreed, that would make it easier for people to find >> >>> > +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. >>> > + >>> Does submit really start the transfer as well? My interpretation of >>> submit is that is only adds desc to a pending queue. When calling >>> issue_pending all these descs will be schedule for DMA transfer. Calls >>> to submit after this point will added to the pending queue again and >>> not be issued until calling issue_pending once more. >> For slave dma devices, submit() is used to start the transaction if the >> channel is idle. If its already doing a transaction then it will queue >> it up and submit once cureent excuting one is completed. It is not >> required to call issue_pending once more. >> I am not sure if this is true for non slave usage, Dan would that be >> correct for you as well? > > No, ->submit() is just an "add this descriptor to the chain" > operation, and ->issue_pending() is always required to make sure the > everything submitted previously is actively executing. ?This was a > holdover from the very first dmaengine implementation where, for > efficiency reasons, it could save mmio writes by batching the issuing > of requests. Thanks Dan for clarifying. Vinod, I propose that the submit and issue_pending works the same for SLAVE and none SLAVE channels. The API should have the same definition independent of DMA_CAP. Please enlighten me if there are things I have foreseen on this matter. Thanks, Per -- 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/