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=-2.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_HIGH,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham 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 1D3B6C468C6 for ; Thu, 19 Jul 2018 09:22:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B910F20856 for ; Thu, 19 Jul 2018 09:22:34 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="eN6xao00" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B910F20856 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727746AbeGSKEr (ORCPT ); Thu, 19 Jul 2018 06:04:47 -0400 Received: from mail.kernel.org ([198.145.29.99]:56294 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726475AbeGSKEr (ORCPT ); Thu, 19 Jul 2018 06:04:47 -0400 Received: from localhost (unknown [106.201.102.32]) (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 D105520671; Thu, 19 Jul 2018 09:22:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1531992152; bh=kpz/abq3EZ5FWyFhtE91WwLwcwUpCYDhIgpYSyGoMFo=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=eN6xao00NNDP0O/XKkX3EWiwNdoIw/Rt7tf1Nt0/7WXsuslciYewWP2zuoOMlk2sk e37MpZv0FmN8Dekm2PrhK0bfz2QxFKvT1glimLtchY7uDeAD9gtSaQ2XPCLJYqJo3k xXaG9BONcFhB/iU3mLJdJjeMbKwCQ0kbpDFINs+4= Date: Thu, 19 Jul 2018 14:52:24 +0530 From: Vinod To: Peter Ujfalusi Cc: radheys@xilinx.com, vinod.koul@intel.com, lars@metafoo.de, michal.simek@xilinx.com, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, dan.j.williams@intel.com, appanad@xilinx.com, linux-arm-kernel@lists.infradead.org Subject: Re: [RFC] dmaengine: Add metadat_ops for dma_async_tx_descriptor Message-ID: <20180719092224.GK3219@vkoul-mobl> References: <32208a9c-2b15-d345-1432-f1e387531f9b@ti.com> <20180601102429.16429-1-peter.ujfalusi@ti.com> <20180710055230.GB3219@vkoul-mobl> <052ebdd9-7e68-5b78-52c3-304376f48777@ti.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <052ebdd9-7e68-5b78-52c3-304376f48777@ti.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter, On 18-07-18, 13:06, Peter Ujfalusi wrote: > >> +struct dma_async_tx_descriptor; > >> + > >> +struct dma_descriptor_metadata_ops { > >> + int (*attach)(struct dma_async_tx_descriptor *desc, void *data, > >> + size_t len); > > > > How does one detach? > > I have not thought about detach, but clients can just attach NULL I guess. So what are the implication of attach and detach here, should the data be deref by dmaengine driver and drop the ref. Should anyone do refcounting? > > > When should the client free up the memory, IOW when > > does dma driver drop ref to data. > > The metadata is for the descriptor so the DMA driver might want to > access to it while the descriptor is valid. > > Typically clients can free up their metadata storage after the dma > completion callback. On DEV_TO_MEM the metadata is going to be placed in > the provided buffer when the transfer is completed. That sounds okay to me > >> + void *(*get_ptr)(struct dma_async_tx_descriptor *desc, > >> + size_t *payload_len, size_t *max_len); > > > > so what is this supposed to do..? > > My issue with the attach in general is that it will need additional > memcpy to move the metadata from/to the client buffer to it's place. > > With get_ptr the client can get the pointer to the actual place where > the metadata resides and modify/read it in place w/o memcpy. > > I know, I know... We need to trust the clients, but with high throughput > peripherals the memcpy is taxing. Okay I am not sure I have understood fully, so with attach you set a pointer (containing metdata?) so why do you need additional one.. > > > > >> + int (*set_len)(struct dma_async_tx_descriptor *desc, > >> + size_t payload_len); > > > > attach already has length, so how does this help? > > So, DMA drivers can implement either or both: > 1. attach() > 2. get_ptr() / set_len() Ah okay, what are the reasons for providing two methods and not a single one > > Clients must not mix the two way of handling the metadata. > The set_len() is intended to tell the DMA driver the client provided > metadata size (in MEM_TO_DEV case mostly). > > MEM_TO_DEV flow on client side: > get_ptr() > fill in the metadata to the pointer (not exceeding max_len) > set_len() to tell the DMA driver the amount of valid bytes written > > DEV_TO_MEM flow on client side: > In the completion callback, get_ptr() > the metadata is payload_len bytes and can be accessed in the return pointer. I would think to unify this.. > BTW: The driver which is going to need this is now accessible in public: > https://git.ti.com/ti-linux-kernel/ti-linux-kernel/trees/ti-linux-4.14.y/drivers/dma/ti > > or in my wip tree: > https://github.com/omap-audio/linux-audio/tree/peter/ti-linux-4.14.y/wip/drivers/dma/ti > > prefixed with k3-* > -- ~Vinod