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 2D909C43603 for ; Fri, 20 Dec 2019 08:01:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7CBA24682 for ; Fri, 20 Dec 2019 08:01:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576828894; bh=WWl2Uh+GDV6mtMcwWgYc9xWAQpXDNNo79AHMa+xx7gw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=fFWAfLzG6uvEjwqLyYFiGMbw+LTPjBNko+IdAfNg1SaQzA/drBw+MISTGTyMB/X7D 4pKkXdwycXB+AU4BeKCRuYh15v3w1wh3/BnRebB7tB3j0nnZX01IKMkoamWFnLi71W LS9JsvQgGph2+NLigAhkEY8zshT2V3KHobsUNX4E= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726327AbfLTIBd (ORCPT ); Fri, 20 Dec 2019 03:01:33 -0500 Received: from mail.kernel.org ([198.145.29.99]:45808 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726210AbfLTIBd (ORCPT ); Fri, 20 Dec 2019 03:01:33 -0500 Received: from localhost (unknown [106.201.107.54]) (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 0224D20716; Fri, 20 Dec 2019 08:01:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1576828892; bh=WWl2Uh+GDV6mtMcwWgYc9xWAQpXDNNo79AHMa+xx7gw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=RuSje8W6JyfDQdto/dU6NUX3Q+1FuB+wXXjYMM1rxvoORUfYg9S9Vo6ul7PuJVYEK ARxwYKgOXqQfd2zaXoXJxB7BZ7MuAXiXWDtJg8m3rFpvKs/3A5ij4zSx2FnY5xPuBF TbiAODwXdH0L+jc5QctifM4m8KfFI9A5er26A5xE= Date: Fri, 20 Dec 2019 13:31:27 +0530 From: Vinod Koul To: Laurent Pinchart Cc: Hyun Kwon , "dmaengine@vger.kernel.org" , Michal Simek , Hyun Kwon , Tejas Upadhyay , Satish Kumar Nagireddy Subject: Re: [PATCH v2 2/4] dma: xilinx: dpdma: Add the Xilinx DisplayPort DMA engine driver Message-ID: <20191220080127.GI2536@vkoul-mobl> References: <20191107021400.16474-1-laurent.pinchart@ideasonboard.com> <20191107021400.16474-3-laurent.pinchart@ideasonboard.com> <20191109175908.GI952516@vkoul-mobl> <20191205150407.GL4734@pendragon.ideasonboard.com> <20191205163909.GH82508@vkoul-mobl> <20191205202746.GA26880@smtp.xilinx.com> <20191208160349.GD14311@pendragon.ideasonboard.com> <20191220051309.GA19504@pendragon.ideasonboard.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191220051309.GA19504@pendragon.ideasonboard.com> Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org Hi Laurent, On 20-12-19, 07:13, Laurent Pinchart wrote: > > OK, in the light of this information I'll keep the two separate and will > > switch to vchan as requested by Vinod. > > I've moved forward with this task, but eventually ran into one hack in > the driver that is more difficult to get rid of than the other ones. > > For display operation, the DPSUB driver needs to submit cyclic > interleaved transfer requests. There's no such thing (as far as I can > tell) in the DMA engine API, so the DPDMA drive simply keeps processing we do support interleave, you need to implement .device_prep_interleaved_dma and use dmaengine_prep_interleaved_dma() from the client > the same descriptor over and over again until a new one is issued. The > hardware supports this with the help of hardware-based chaining of > descriptors, and the DPDMA driver simply sets the next pointer of the > descriptor to itself. > > How can I solve this in a way that wouldn't abuse the DMA engine API ? Is this not a cyclic case of descriptor? -- ~Vinod