From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752433Ab3GHOyZ (ORCPT ); Mon, 8 Jul 2013 10:54:25 -0400 Received: from smtp-out-123.synserver.de ([212.40.185.123]:1067 "EHLO smtp-out-123.synserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751894Ab3GHOyY (ORCPT ); Mon, 8 Jul 2013 10:54:24 -0400 X-SynServer-TrustedSrc: 1 X-SynServer-AuthUser: lars@metafoo.de X-SynServer-PPID: 16180 Message-ID: <51DAD2C3.8070203@metafoo.de> Date: Mon, 08 Jul 2013 16:54:59 +0200 From: Lars-Peter Clausen User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130116 Icedove/10.0.12 MIME-Version: 1.0 To: Vinod Koul CC: Dan Williams , Linux Kernel Mailing List , Matt Porter Subject: Re: [RFC] dmaengine: add dma_slave_get_caps api References: <1373273650-31097-1-git-send-email-vinod.koul@intel.com> <51DAAA1F.5050002@metafoo.de> <20130708134024.GH16653@intel.com> <51DACC8D.5020201@metafoo.de> <20130708140357.GI16653@intel.com> In-Reply-To: <20130708140357.GI16653@intel.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/08/2013 04:03 PM, Vinod Koul wrote: > On Mon, Jul 08, 2013 at 04:28:29PM +0200, Lars-Peter Clausen wrote: >> On 07/08/2013 03:40 PM, Vinod Koul wrote: >>> On Mon, Jul 08, 2013 at 02:01:35PM +0200, Lars-Peter Clausen wrote: >>>> On 07/08/2013 10:54 AM, Vinod Koul wrote: >>>>> +/* struct dma_slave_caps - expose capabilities of a slave channel only >>>>> + * >>>>> + * @src_addr_widths: bit mask of src addr widths the channel supports >>>>> + * @dstn_addr_widths: bit mask of dstn addr widths the channel supports >>>>> + * @src_burst_lengths: bit mask of src slave burst lengths supported >>>>> + * @dstn_burst_lengths: bit mask of dstn slave burst lengths supported >>>> >>>> I'm not sure if we need the burst_lengths fields. For one we can only >>>> express a max burst length up 32. And usually it is fine if the dma >>>> controller does not support the burst length requested by the slave driver, >>>> since this only specifies the maximum and the dma controller driver can >>>> choose a value below this limit. E.g. if the max burst length is set to 16 >>>> it is still fine if the controller only supports a burst length of 8. >>> well how are you picking up which one to use? >>> The idea is that you query and match that with system and client to get best >>> throughput. If you have IP block which over generations change capablities you >>> can runtime query and then program the channel smartly! >> >> The client would always request the largest burst size it can support, and >> the dma master would then select a burst size equal or smaller to it >> depending on what it can support. > not really, most dmac drivers will return an error when they find a value is not > in the supported list. And that is precisely what we would like to prevent. > If you look at current model, it mostly program value which we know is already > a capablity and works model. The majority of the DMA drivers will either accept any maxburst value (which is probably broken) or round down. The only ones which accept only a fixed set of burst sizes seem to be mmp_pdma, mmp_tdma and sa11x0-dma. - Lars