From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753508AbbHUI1f (ORCPT ); Fri, 21 Aug 2015 04:27:35 -0400 Received: from mga03.intel.com ([134.134.136.65]:65523 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751518AbbHUI1a (ORCPT ); Fri, 21 Aug 2015 04:27:30 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.15,720,1432623600"; d="scan'208";a="772984694" Date: Fri, 21 Aug 2015 13:59:39 +0530 From: Vinod Koul To: Sudeep Dutt Cc: Ashutosh Dixit , Greg Kroah-Hartman , Dan Williams , linux-kernel@vger.kernel.org, Nikhil Rao , Siva Yerramreddy Subject: Re: [PATCH char-misc-next 11/19] dma: Add support to program MIC x100 status descriptiors Message-ID: <20150821082939.GL13546@localhost> References: <0c2dec1519fdd81dfe6335efc2a1edb0b142639b.1438040669.git.ashutosh.dixit@intel.com> <20150820052014.GU13546@localhost> <1440091850.115234.110.camel@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1440091850.115234.110.camel@localhost> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 20, 2015 at 10:30:50AM -0700, Sudeep Dutt wrote: > On Thu, 2015-08-20 at 10:50 +0530, Vinod Koul wrote: > > On Mon, Jul 27, 2015 at 04:58:17PM -0700, Ashutosh Dixit wrote: > > > + /* > > > + * This is a hack to program status descriptor since > > > + * DMA engine API doesn't have support for this. > > > + */ > > what do you mean by programming status descriptor, what do you need to > > program? > > > > The MIC X100 DMA engine has a special status descriptor which writes an > 8 byte immediate data value to a destination address. It is used to > signal completion of all DMA descriptors prior to the status descriptor. > The DMA engine API does not allow drivers to pass a 8 byte value. We are > allowed to pass a source physical address but we cannot determine the > source value within the DMA driver using that information specifically > with the IOMMU enabled. We have added this workaround so that we can > program this special status update descriptor without making any changes > to the DMA engine API. I think this is a special case so you should export an API and let client program using that API. -- ~Vinod