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=-2.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_PASS 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 EEE65C37120 for ; Mon, 21 Jan 2019 20:24:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B5F9B20844 for ; Mon, 21 Jan 2019 20:24:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ti.com header.i=@ti.com header.b="vvydNmFy" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728219AbfAUUYa (ORCPT ); Mon, 21 Jan 2019 15:24:30 -0500 Received: from lelv0143.ext.ti.com ([198.47.23.248]:41754 "EHLO lelv0143.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727384AbfAUUYY (ORCPT ); Mon, 21 Jan 2019 15:24:24 -0500 Received: from fllv0035.itg.ti.com ([10.64.41.0]) by lelv0143.ext.ti.com (8.15.2/8.15.2) with ESMTP id x0LKOAIV085156; Mon, 21 Jan 2019 14:24:10 -0600 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ti.com; s=ti-com-17Q1; t=1548102250; bh=Y6clMbjs3UAgpjX9jOCJO8phMjQgQnd5LACs21ik7GU=; h=Subject:To:CC:References:From:Date:In-Reply-To; b=vvydNmFyrRd12Md7aIjUXK8g/ROpNmVPNct39mNHQ295drwdIuCLd4/+agvoT28/a YA3OztcA0KIyRYQz4UGDfcm117xUD8kZUAasZCs2C72gQKrbgUKlIl7oCG8rdcTKkJ SDv5el2ZQ0akZNlBtdrpIP1YVfqM2Civ8vS5mAyQ= Received: from DLEE104.ent.ti.com (dlee104.ent.ti.com [157.170.170.34]) by fllv0035.itg.ti.com (8.15.2/8.15.2) with ESMTPS id x0LKOA45041379 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=FAIL); Mon, 21 Jan 2019 14:24:10 -0600 Received: from DLEE102.ent.ti.com (157.170.170.32) by DLEE104.ent.ti.com (157.170.170.34) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1591.10; Mon, 21 Jan 2019 14:24:10 -0600 Received: from dflp32.itg.ti.com (10.64.6.15) by DLEE102.ent.ti.com (157.170.170.32) with Microsoft SMTP Server (version=TLS1_0, cipher=TLS_RSA_WITH_AES_256_CBC_SHA) id 15.1.1591.10 via Frontend Transport; Mon, 21 Jan 2019 14:24:10 -0600 Received: from [172.22.66.82] (ileax41-snat.itg.ti.com [10.172.224.153]) by dflp32.itg.ti.com (8.14.3/8.13.8) with ESMTP id x0LKO9Lb029285; Mon, 21 Jan 2019 14:24:09 -0600 Subject: Re: [PATCH 3/4] dma-buf: add support for mapping with dma mapping attributes To: Liam Mark CC: Christoph Hellwig , Laura Abbott , , , , , , , , , , , References: <1547836667-13695-1-git-send-email-lmark@codeaurora.org> <1547836667-13695-4-git-send-email-lmark@codeaurora.org> <20190119102527.GA17723@infradead.org> <7ae73c39-9049-bcf6-775f-b0817ba0ec5f@redhat.com> <20190121083046.GD12420@infradead.org> <0ed7875f-15e9-184f-5b99-9a53df7c8d14@ti.com> From: "Andrew F. Davis" Message-ID: <4925c9db-fc73-1ccb-1766-ef68d014d55a@ti.com> Date: Mon, 21 Jan 2019 14:24:09 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-EXCLAIMER-MD-CONFIG: e1e8a2fd-e40a-4ac6-ac9b-f7e9cc9ee180 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 1/21/19 2:20 PM, Liam Mark wrote: > On Mon, 21 Jan 2019, Andrew F. Davis wrote: > >> On 1/21/19 1:44 PM, Liam Mark wrote: >>> On Mon, 21 Jan 2019, Christoph Hellwig wrote: >>> >>>> On Sat, Jan 19, 2019 at 08:50:41AM -0800, Laura Abbott wrote: >>>>>> And who is going to decide which ones to pass? And who documents >>>>>> which ones are safe? >>>>>> >>>>>> I'd much rather have explicit, well documented dma-buf flags that >>>>>> might get translated to the DMA API flags, which are not error checked, >>>>>> not very well documented and way to easy to get wrong. >>>>>> >>>>> >>>>> I'm not sure having flags in dma-buf really solves anything >>>>> given drivers can use the attributes directly with dma_map >>>>> anyway, which is what we're looking to do. The intention >>>>> is for the driver creating the dma_buf attachment to have >>>>> the knowledge of which flags to use. >>>> >>>> Well, there are very few flags that you can simply use for all calls of >>>> dma_map*. And given how badly these flags are defined I just don't want >>>> people to add more places where they indirectly use these flags, as >>>> it will be more than enough work to clean up the current mess. >>>> >>>> What flag(s) do you want to pass this way, btw? Maybe that is where >>>> the problem is. >>>> >>> >>> The main use case is for allowing clients to pass in >>> DMA_ATTR_SKIP_CPU_SYNC in order to skip the default cache maintenance >>> which happens in dma_buf_map_attachment and dma_buf_unmap_attachment. In >>> ION the buffers aren't usually accessed from the CPU so this allows >>> clients to often avoid doing unnecessary cache maintenance. >>> >> >> How can a client know that no CPU access has occurred that needs to be >> flushed out? >> > > I have left this to clients, but if they own the buffer they can have the > knowledge as to whether CPU access is needed in that use case (example for > post-processing). > > For example with the previous version of ION we left all decisions of > whether cache maintenance was required up to the client, they would use > the ION cache maintenance IOCTL to force cache maintenance only when it > was required. > In these cases almost all of the access was being done by the device and > in the rare cases CPU access was required clients would initiate the > required cache maintenance before and after the CPU access. > I think we have different definitions of "client", I'm talking about the DMA-BUF client (the importer), that is who can set this flag. It seems you mean the userspace application, which has no control over this flag. > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > a Linux Foundation Collaborative Project > From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Andrew F. Davis" Subject: Re: [PATCH 3/4] dma-buf: add support for mapping with dma mapping attributes Date: Mon, 21 Jan 2019 14:24:09 -0600 Message-ID: <4925c9db-fc73-1ccb-1766-ef68d014d55a@ti.com> References: <1547836667-13695-1-git-send-email-lmark@codeaurora.org> <1547836667-13695-4-git-send-email-lmark@codeaurora.org> <20190119102527.GA17723@infradead.org> <7ae73c39-9049-bcf6-775f-b0817ba0ec5f@redhat.com> <20190121083046.GD12420@infradead.org> <0ed7875f-15e9-184f-5b99-9a53df7c8d14@ti.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: driverdev-devel-bounces@linuxdriverproject.org Sender: "devel" To: Liam Mark Cc: devel@driverdev.osuosl.org, linaro-mm-sig@lists.linaro.org, tkjos@android.com, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Christoph Hellwig , arve@android.com, john.stultz@linaro.org, joel@joelfernandes.org, maco@android.com, sumit.semwal@linaro.org, christian@brauner.io List-Id: dri-devel@lists.freedesktop.org On 1/21/19 2:20 PM, Liam Mark wrote: > On Mon, 21 Jan 2019, Andrew F. Davis wrote: > >> On 1/21/19 1:44 PM, Liam Mark wrote: >>> On Mon, 21 Jan 2019, Christoph Hellwig wrote: >>> >>>> On Sat, Jan 19, 2019 at 08:50:41AM -0800, Laura Abbott wrote: >>>>>> And who is going to decide which ones to pass? And who documents >>>>>> which ones are safe? >>>>>> >>>>>> I'd much rather have explicit, well documented dma-buf flags that >>>>>> might get translated to the DMA API flags, which are not error checked, >>>>>> not very well documented and way to easy to get wrong. >>>>>> >>>>> >>>>> I'm not sure having flags in dma-buf really solves anything >>>>> given drivers can use the attributes directly with dma_map >>>>> anyway, which is what we're looking to do. The intention >>>>> is for the driver creating the dma_buf attachment to have >>>>> the knowledge of which flags to use. >>>> >>>> Well, there are very few flags that you can simply use for all calls of >>>> dma_map*. And given how badly these flags are defined I just don't want >>>> people to add more places where they indirectly use these flags, as >>>> it will be more than enough work to clean up the current mess. >>>> >>>> What flag(s) do you want to pass this way, btw? Maybe that is where >>>> the problem is. >>>> >>> >>> The main use case is for allowing clients to pass in >>> DMA_ATTR_SKIP_CPU_SYNC in order to skip the default cache maintenance >>> which happens in dma_buf_map_attachment and dma_buf_unmap_attachment. In >>> ION the buffers aren't usually accessed from the CPU so this allows >>> clients to often avoid doing unnecessary cache maintenance. >>> >> >> How can a client know that no CPU access has occurred that needs to be >> flushed out? >> > > I have left this to clients, but if they own the buffer they can have the > knowledge as to whether CPU access is needed in that use case (example for > post-processing). > > For example with the previous version of ION we left all decisions of > whether cache maintenance was required up to the client, they would use > the ION cache maintenance IOCTL to force cache maintenance only when it > was required. > In these cases almost all of the access was being done by the device and > in the rare cases CPU access was required clients would initiate the > required cache maintenance before and after the CPU access. > I think we have different definitions of "client", I'm talking about the DMA-BUF client (the importer), that is who can set this flag. It seems you mean the userspace application, which has no control over this flag. > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > a Linux Foundation Collaborative Project >