Subject: Re: [PATCH char-misc-next 11/19] dma: Add support to program MIC
 x100 status descriptiors
From: Sudeep Dutt <sudeep.dutt@intel.com>
To: Vinod Koul <vinod.koul@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Dan Williams <dan.j.williams@intel.com>, linux-kernel@vger.kernel.org,
        Nikhil Rao <nikhil.rao@intel.com>,
        Siva Yerramreddy <yshivakrishna@gmail.com>,
        Sudeep Dutt <sudeep.dutt@intel.com>
In-Reply-To: <20150821082939.GL13546@localhost>
References: <cover.1438040669.git.ashutosh.dixit@intel.com>
	 <0c2dec1519fdd81dfe6335efc2a1edb0b142639b.1438040669.git.ashutosh.dixit@intel.com>
	 <20150820052014.GU13546@localhost> <1440091850.115234.110.camel@localhost>
	 <20150821082939.GL13546@localhost>
Content-Type: text/plain; charset="UTF-8"
Date: Fri, 21 Aug 2015 09:14:13 -0700
Message-ID: <1440173653.115234.123.camel@localhost>
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1630
Lines: 38

On Fri, 2015-08-21 at 13:59 +0530, Vinod Koul wrote:
> 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.
> 

Sounds good. We will export a new API from the MIC X100 DMA driver in
the next revision of this patch series.

Thanks for the review!

Sudeep Dutt

--
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/