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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 7DF8EC433E3 for ; Wed, 20 May 2020 18:05:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 57CB4204EF for ; Wed, 20 May 2020 18:05:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="Gkqd7eG/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726819AbgETSFC (ORCPT ); Wed, 20 May 2020 14:05:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33626 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726560AbgETSFC (ORCPT ); Wed, 20 May 2020 14:05:02 -0400 Received: from mail-wr1-x444.google.com (mail-wr1-x444.google.com [IPv6:2a00:1450:4864:20::444]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9B1DEC061A0E for ; Wed, 20 May 2020 11:05:00 -0700 (PDT) Received: by mail-wr1-x444.google.com with SMTP id e16so4089458wra.7 for ; Wed, 20 May 2020 11:05:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=7VLWQjSGehoQQ10TIMLPZjQP7xmwIhJsBUGDoa1VrTI=; b=Gkqd7eG/0dnXjHy1xG1j6m7TgceuOsXw1H/rc22l7IJlPhwJ2B6P2ljAHXrYzTRdar MIaXDobt3I0ohzfnM8+IrTc0qKhgEUwuY7/Fo9s2GXiixg4EmEP6C4/NiXdh9NUFhFJv EkITnRLky4apVZDMRRGPfnmoIfrxMMPEjnOeE= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=7VLWQjSGehoQQ10TIMLPZjQP7xmwIhJsBUGDoa1VrTI=; b=RVfvQxsn+rxSKot0xCWUvULpXQtHInHVlzibCjLLXtBYOHQTVrpXUAVCtT31OQcV2C eZ+1p4gBgcZEXwpwrlYu+Rn6h7rGfGXcTswjyvYLb7QRN1GJy9co4pe/BctTd716BOzA 5BWfthMaBhND4JZa+EHE1XQwNm88C6n+curb53qDkdvyc7fh/RJ9Jln4B6wpjQAOPNkd nYydYJFILXgfrgqtxW2bcMmb72tnFxjg01ezAa9tNPzvbkiDKZjivTGcKgwxx8z1n9Kf Qsins6aymUNHSGjxQE4rj41YYQfDvjiL/EF+U0TkpfZFu3eBqSQhAEaYPmDbskkvE/P7 nvHg== X-Gm-Message-State: AOAM533S4IAV0qxJQKI3bBIuLW4eVUGdgkgrBCoozzjlsmArX82kATRI SUVwik0R4XWwnso+vDXMriYX8g== X-Google-Smtp-Source: ABdhPJyS/wpov4LAbGyHkjwZQ9PTa7H2uWj92iFIX5HPBrejAjzuIvVfeVBaSJI7TyMuvzzPHXcGHg== X-Received: by 2002:adf:ec87:: with SMTP id z7mr5634315wrn.149.1589997899278; Wed, 20 May 2020 11:04:59 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id b12sm4040708wmj.0.2020.05.20.11.04.57 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 May 2020 11:04:58 -0700 (PDT) Date: Wed, 20 May 2020 20:04:56 +0200 From: Daniel Vetter To: Oded Gabbay Cc: Daniel Vetter , Dave Airlie , Greg Kroah-Hartman , Intel Graphics Development , LKML , DRI Development , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Olof Johansson , Daniel Vetter , Sumit Semwal , Linux Media Mailing List Subject: Re: [Intel-gfx] [PATCH 3/3] misc/habalabs: don't set default fence_ops->wait Message-ID: <20200520180456.GC206103@phenom.ffwll.local> Mail-Followup-To: Oded Gabbay , Dave Airlie , Greg Kroah-Hartman , Intel Graphics Development , LKML , DRI Development , "moderated list:DMA BUFFER SHARING FRAMEWORK" , Olof Johansson , Daniel Vetter , Sumit Semwal , Linux Media Mailing List References: <20200511091142.208787-1-daniel.vetter@ffwll.ch> <20200511091142.208787-3-daniel.vetter@ffwll.ch> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Operating-System: Linux phenom 5.6.0-1-amd64 Sender: linux-media-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-media@vger.kernel.org On Thu, May 14, 2020 at 02:38:38PM +0300, Oded Gabbay wrote: > On Tue, May 12, 2020 at 9:12 AM Daniel Vetter wrote: > > > > On Tue, May 12, 2020 at 4:14 AM Dave Airlie wrote: > > > > > > On Mon, 11 May 2020 at 19:37, Oded Gabbay wrote: > > > > > > > > On Mon, May 11, 2020 at 12:11 PM Daniel Vetter wrote: > > > > > > > > > > It's the default. > > > > Thanks for catching that. > > > > > > > > > > > > > > Also so much for "we're not going to tell the graphics people how to > > > > > review their code", dma_fence is a pretty core piece of gpu driver > > > > > infrastructure. And it's very much uapi relevant, including piles of > > > > > corresponding userspace protocols and libraries for how to pass these > > > > > around. > > > > > > > > > > Would be great if habanalabs would not use this (from a quick look > > > > > it's not needed at all), since open source the userspace and playing > > > > > by the usual rules isn't on the table. If that's not possible (because > > > > > it's actually using the uapi part of dma_fence to interact with gpu > > > > > drivers) then we have exactly what everyone promised we'd want to > > > > > avoid. > > > > > > > > We don't use the uapi parts, we currently only using the fencing and > > > > signaling ability of this module inside our kernel code. But maybe I > > > > didn't understand what you request. You want us *not* to use this > > > > well-written piece of kernel code because it is only used by graphics > > > > drivers ? > > > > I'm sorry but I don't get this argument, if this is indeed what you meant. > > > > > > We would rather drivers using a feature that has requirements on > > > correct userspace implementations of the feature have a userspace that > > > is open source and auditable. > > > > > > Fencing is tricky, cross-device fencing is really tricky, and having > > > the ability for a closed userspace component to mess up other people's > > > drivers, think i915 shared with closed habana userspace and shared > > > fences, decreases ability to debug things. > > > > > > Ideally we wouldn't offer users known untested/broken scenarios, so > > > yes we'd prefer that drivers that intend to expose a userspace fencing > > > api around dma-fence would adhere to the rules of the gpu drivers. > > > > > > I'm not say you have to drop using dma-fence, but if you move towards > > > cross-device stuff I believe other drivers would be correct in > > > refusing to interact with fences from here. > > > > The flip side is if you only used dma-fence.c "because it's there", > > and not because it comes with an uapi attached and a cross-driver > > kernel internal contract for how to interact with gpu drivers, then > > there's really not much point in using it. It's a custom-rolled > > wait_queue/event thing, that's all. Without the gpu uapi and gpu > > cross-driver contract it would be much cleaner to just use wait_queue > > directly, and that's a construct all kernel developers understand, not > > just gpu folks. From a quick look at least habanalabs doesn't use any > > of these uapi/cross-driver/gpu bits. > > -Daniel > > Hi Daniel, > I want to say explicitly that we don't use the dma-buf uapi parts, nor > we intend to use them to communicate with any GPU device. We only use > it as simple completion mechanism as it was convenient to use. > I do understand I can exchange that mechanism with a simpler one, and > I will add an internal task to do it (albeit not in a very high > priority) and upstream it, its just that it is part of our data path > so we need to thoroughly validate it first. Sounds good. Wrt merging this patch here, can you include that in one of your next pulls? Or should I toss it entirely, waiting for you to remove dma_fence outright? Thanks, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch