From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F418EC2BA83 for ; Thu, 13 Feb 2020 13:29:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8CA224649 for ; Thu, 13 Feb 2020 13:29:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581600584; bh=b/vSfjvGHGTciw0MDBenTQGqezCZ4ESA01KHETJSEiE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=egVAe42wG+Tx5wE8UzXDv6cjkM9E2BeNqV92evTOOYASVuPCaZvRjkXP7tBEITauj H+ILks+JCeut3gBBBUlvBCoxfKveQXrouORKb6z5VzEMg+5l0Z1ATTFIMUgm02xHd4 hHjXfbii3Uj4eK7kcrUl2X/ptyETf3xnf6OuvFP0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729801AbgBMN3o (ORCPT ); Thu, 13 Feb 2020 08:29:44 -0500 Received: from mail.kernel.org ([198.145.29.99]:60840 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729588AbgBMN3o (ORCPT ); Thu, 13 Feb 2020 08:29:44 -0500 Received: from localhost (unknown [106.201.58.38]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id CA9DD222C2; Thu, 13 Feb 2020 13:29:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581600583; bh=b/vSfjvGHGTciw0MDBenTQGqezCZ4ESA01KHETJSEiE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=a/dvp+DjTMOU2RXfC/YTY90NITzT7EebQINaZqkAJStRqeahxS/T7BDn/OBveeXoA aWykPQSFS9o3kTNF2T0hBvfmze9i4+wOGQjhI5aA3/UCIcNugIeT0dmgNx6o2LzEkU oi3+tA8Jf9VGMn/fWCVFH11qfeTJ0lGZgBNBs66k= Date: Thu, 13 Feb 2020 18:59:38 +0530 From: Vinod Koul To: Laurent Pinchart Cc: Peter Ujfalusi , dmaengine@vger.kernel.org, Michal Simek , Hyun Kwon , Tejas Upadhyay , Satish Kumar Nagireddy Subject: Re: [PATCH v3 2/6] dmaengine: Add interleaved cyclic transaction type Message-ID: <20200213132938.GF2618@vkoul-mobl> References: <20200123022939.9739-1-laurent.pinchart@ideasonboard.com> <20200123022939.9739-3-laurent.pinchart@ideasonboard.com> <2f3a9e9e-9b74-7c2e-de3a-4897ab0e8205@ti.com> <20200123084352.GU2841@vkoul-mobl> <88aa9920-cdaf-97f0-c36f-66a998860ed2@ti.com> <20200123122304.GB13922@pendragon.ideasonboard.com> <20200124061047.GE2841@vkoul-mobl> <20200124085051.GA4842@pendragon.ideasonboard.com> <20200210140618.GA4727@pendragon.ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200210140618.GA4727@pendragon.ideasonboard.com> Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org Hi Laurent, On 10-02-20, 16:06, Laurent Pinchart wrote: > > >> The use case here is not to switch to a new configuration, but to switch > > >> to a new buffer. If the transfer had to be terminated manually first, > > >> the DMA engine would potentially miss a frame, which is not acceptable. > > >> We need an atomic way to switch to the next transfer. > > > > > > So in this case you have, let's say a cyclic descriptor with N buffers > > > and they are cyclically capturing data and providing to client/user.. > > > > For the display case it's cyclic over a single buffer that is repeatedly > > displayed over and over again until a new one replaces it, when > > userspace wants to change the content on the screen. Userspace only has > > to provide a new buffer when content changes, otherwise the display has > > to keep displaying the same one. > > Is the use case clear enough, or do you need more information ? Are you > fine with the API for this kind of use case ? So we *know* when a new buffer is being used? IOW would it be possible for display (rather a dmaengine facing display wrapper) to detect that we are reusing an old buffer and keep the cyclic and once detected prepare a new descriptor, submit a new one and then terminate old one which should trigger next transaction to be submitted Would that make sense here? -- ~Vinod