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=-7.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 B3379C433F5 for ; Mon, 13 Sep 2021 10:17:00 +0000 (UTC) Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 786066101C for ; Mon, 13 Sep 2021 10:17:00 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 786066101C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2EF076E11F; Mon, 13 Sep 2021 10:16:55 +0000 (UTC) Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by gabe.freedesktop.org (Postfix) with ESMTPS id 4CD1189CAA; Mon, 13 Sep 2021 10:16:53 +0000 (UTC) X-IronPort-AV: E=McAfee;i="6200,9189,10105"; a="221671981" X-IronPort-AV: E=Sophos;i="5.85,288,1624345200"; d="scan'208";a="221671981" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Sep 2021 03:16:52 -0700 X-IronPort-AV: E=Sophos;i="5.85,288,1624345200"; d="scan'208";a="481263968" Received: from vdvoloki-mobl.ccr.corp.intel.com (HELO [10.249.254.107]) ([10.249.254.107]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Sep 2021 03:16:51 -0700 To: =?UTF-8?Q?Christian_K=c3=b6nig?= , intel-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org Cc: maarten.lankhorst@linux.intel.com, matthew.auld@intel.com, Matthew Auld References: <20210910131512.161655-1-thomas.hellstrom@linux.intel.com> <5ea3f498cc5ae84fa6aeba97a64e4eb8ab32e02b.camel@linux.intel.com> <5ca10e93-9bac-bd8f-39b0-d60fe06bc289@amd.com> From: =?UTF-8?Q?Thomas_Hellstr=c3=b6m?= Message-ID: <4b9e25e3-0a9d-a7a8-e092-8355c6b5878f@linux.intel.com> Date: Mon, 13 Sep 2021 12:16:48 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <5ca10e93-9bac-bd8f-39b0-d60fe06bc289@amd.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Content-Language: en-US Subject: Re: [Intel-gfx] [RFC PATCH] drm/ttm: Add a private member to the struct ttm_resource X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 9/13/21 11:41 AM, Christian König wrote: > Am 13.09.21 um 11:36 schrieb Thomas Hellström: >> On 9/13/21 8:17 AM, Christian König wrote: >>> Am 11.09.21 um 08:07 schrieb Thomas Hellström: >>>> On Fri, 2021-09-10 at 19:03 +0200, Christian König wrote: >>>>> Am 10.09.21 um 17:30 schrieb Thomas Hellström: >>>>>> On Fri, 2021-09-10 at 16:40 +0200, Christian König wrote: >>>>>>> Am 10.09.21 um 15:15 schrieb Thomas Hellström: >>>>>>>> Both the provider (resource manager) and the consumer (the TTM >>>>>>>> driver) >>>>>>>> want to subclass struct ttm_resource. Since this is left for >>>>>>>> the >>>>>>>> resource >>>>>>>> manager, we need to provide a private pointer for the TTM >>>>>>>> driver. >>>>>>>> >>>>>>>> Provide a struct ttm_resource_private for the driver to >>>>>>>> subclass >>>>>>>> for >>>>>>>> data with the same lifetime as the struct ttm_resource: In the >>>>>>>> i915 >>>>>>>> case >>>>>>>> it will, for example, be an sg-table and radix tree into the >>>>>>>> LMEM >>>>>>>> /VRAM pages that currently are awkwardly attached to the GEM >>>>>>>> object. >>>>>>>> >>>>>>>> Provide an ops structure for associated ops (Which is only >>>>>>>> destroy() ATM) >>>>>>>> It might seem pointless to provide a separate ops structure, >>>>>>>> but >>>>>>>> Linus >>>>>>>> has previously made it clear that that's the norm. >>>>>>>> >>>>>>>> After careful audit one could perhaps also on a per-driver >>>>>>>> basis >>>>>>>> replace the delete_mem_notify() TTM driver callback with the >>>>>>>> above >>>>>>>> destroy function. >>>>>>> Well this is a really big NAK to this approach. >>>>>>> >>>>>>> If you need to attach some additional information to the resource >>>>>>> then >>>>>>> implement your own resource manager like everybody else does. >>>>>> Well this was the long discussion we had back then when the >>>>>> resource >>>>>> mangagers started to derive from struct resource and I was under >>>>>> the >>>>>> impression that we had come to an agreement about the different >>>>>> use- >>>>>> cases here, and this was my main concern. >>>>> Ok, then we somehow didn't understood each other. >>>>> >>>>>> I mean, it's a pretty big layer violation to do that for this use- >>>>>> case. >>>>> Well exactly that's the point. TTM should not have a layer design in >>>>> the >>>>> first place. >>>>> >>>>> Devices, BOs, resources etc.. are base classes which should implement >>>>> a >>>>> base functionality which is then extended by the drivers to implement >>>>> the driver specific functionality. >>>>> >>>>> That is a component based approach, and not layered at all. >>>>> >>>>>> The TTM resource manager doesn't want to know about this data at >>>>>> all, >>>>>> it's private to the ttm resource user layer and the resource >>>>>> manager >>>>>> works perfectly well without it. (I assume the other drivers that >>>>>> implement their own resource managers need the data that the >>>>>> subclassing provides?) >>>>> Yes, that's exactly why we have the subclassing. >>>>> >>>>>> The fundamental problem here is that there are two layers wanting >>>>>> to >>>>>> subclass struct ttm_resource. That means one layer gets to do that, >>>>>> the >>>>>> second gets to use a private pointer, (which in turn can provide >>>>>> yet >>>>>> another private pointer to a potential third layer). With your >>>>>> suggestion, the second layer instead is forced to subclass each >>>>>> subclassed instance it uses from  the first layer provides? >>>>> Well completely drop the layer approach/thinking here. >>>>> >>>>> The resource is an object with a base class. The base class >>>>> implements >>>>> the interface TTM needs to handle the object, e.g. >>>>> create/destroy/debug >>>>> etc... >>>>> >>>>> Then we need to subclass this object because without any additional >>>>> information the object is pretty pointless. >>>>> >>>>> One possibility for this is to use the range manager to implement >>>>> something drm_mm based. BTW: We should probably rename that to >>>>> something >>>>> like ttm_res_drm_mm or similar. >>>> Sure I'm all in on that, but my point is this becomes pretty awkward >>>> because the reusable code already subclasses struct ttm_resource. Let >>>> me give you an example: >>>> >>>> Prereqs: >>>> 1) We want to be able to re-use resource manager implementations among >>>> drivers. >>>> 2) A driver might want to re-use multiple implementations and have >>>> identical data "struct i915_data" attached to both >>> >>> Well that's the point I don't really understand. Why would a driver >>> want to do this? >> >> Let's say you have a struct ttm_object_vram and a struct >> ttm_object_gtt, both subclassing drm_gem_object. Then I'd say a >> driver would want to subclass those to attach identical data, extend >> functionality and provide a single i915_gem_object to the rest of the >> driver, which couldn't care less whether it's vram or gtt? Wouldn't >> you say having separate struct ttm_object_vram and a struct >> ttm_object_gtt in this case would be awkward?. We *want* to allow >> common handling. > > Yeah, but that's a bad idea. This is like diamond inheritance in C++. > > When you need the same functionality in different backends you > implement that as separate object and then add a parent class. > >> >> It's the exact same situation here. With struct ttm_resource you let >> *different* implementation flavours subclass it, which makes it >> awkward for the driver to extend the functionality in a common way by >> subclassing, unless the driver only uses a single implementation. > > Well the driver should use separate implementations for their > different domains as much as possible. > Hmm, Now you lost me a bit. Are you saying that the way we do dynamic backends in the struct ttm_buffer_object to facilitate driver subclassing is a bad idea or that the RFC with backpointer is a bad idea? If the latter, I can agree with that, but could we perhaps then work to find a way to turn the common manager (or in the future perhaps managers) into helpers that doesn't embed struct ttm_resource rather than a full-fledged resource manager. Then the driver will always be responsible for embedding the struct ttm_resource and combines helpers as it sees fit? Thanks, /Thomas