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 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 0B4B0C54E8D for ; Tue, 12 May 2020 06:12:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA12020769 for ; Tue, 12 May 2020 06:12:24 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="GJU6+oDm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726726AbgELGMX (ORCPT ); Tue, 12 May 2020 02:12:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44950 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S1725933AbgELGMX (ORCPT ); Tue, 12 May 2020 02:12:23 -0400 Received: from mail-ot1-x342.google.com (mail-ot1-x342.google.com [IPv6:2607:f8b0:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7D1AFC061A0E for ; Mon, 11 May 2020 23:12:23 -0700 (PDT) Received: by mail-ot1-x342.google.com with SMTP id t3so9611210otp.3 for ; Mon, 11 May 2020 23:12:23 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=rDVhfwcqSVyx9q5/p16CBADSN5ABq1zW6fY3UNoJRwE=; b=GJU6+oDml8xnoT95xGt/51ibXnSnWHbS6L44A1d4aAxTIhM+TRN0GsMjxc6tOiQxij W1HgnyhjOqVZ4EeXD2+Ya67BUUhQZNpILTKhwGGkEyj+lgqcYywNl95I6T/MARS6UR7u VIlXBE4FZi1iC3oSuefMY08HMZx+TFAs4C+u0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=rDVhfwcqSVyx9q5/p16CBADSN5ABq1zW6fY3UNoJRwE=; b=CUUgoyBW7sPKKLIHrr+4ibiT5/cPIGqr7VODYzQgWN8cIdoNvaCjEpTTT2X0YYb73r gcHYKKUlcp2lzWejwn4afoulzd/MxPcaWOaqutMuAcWfPGckO2IMzLsHTESId/WrICiC gJKb94KD72z6MRMFqaK/4Hzzklhi6iiNNiP9yHmv3apNdev8Vul8APMaWfJ63LOx27G0 aeGwxhtAVJe8OpO044hlCMBs5h1Ev0rb5qmDGH6J40OqVe9QOse7baX5w+JGTt6f3vSO QO/4fgo1xhHhWkh3YAayF19GUAbt1B7jXyFRlpGjqUFcPovagusZzZJVHi4yvX85WlfN KVqQ== X-Gm-Message-State: AGi0PuY5imtD0t1TQz6mYd9XKSi0TZFOqeUeshSy1sTpjBPGtgjip+0z 6XeTE+Frzql6KSlN2scAzISi0tXb6iXF7SARmMPf4aoQ X-Google-Smtp-Source: APiQypJhNRGRhinzAhGDFhJNon3eFMcfMUO5uhBHXbuwUw5/kLPwp8toKCD2lNCnnnIIniHhPlp9X7sj/2mlYxXCY6k= X-Received: by 2002:a05:6830:1d0:: with SMTP id r16mr14792604ota.303.1589263942718; Mon, 11 May 2020 23:12:22 -0700 (PDT) MIME-Version: 1.0 References: <20200511091142.208787-1-daniel.vetter@ffwll.ch> <20200511091142.208787-3-daniel.vetter@ffwll.ch> In-Reply-To: From: Daniel Vetter Date: Tue, 12 May 2020 08:12:11 +0200 Message-ID: Subject: Re: [Intel-gfx] [PATCH 3/3] misc/habalabs: don't set default fence_ops->wait To: Dave Airlie Cc: Oded Gabbay , 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 Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch