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=-3.9 required=3.0 tests=BAYES_00,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 5514FC43461 for ; Tue, 8 Sep 2020 17:57:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C66B42074B for ; Tue, 8 Sep 2020 17:57:03 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=ffwll.ch header.i=@ffwll.ch header.b="TRI4o8zL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732193AbgIHRxr (ORCPT ); Tue, 8 Sep 2020 13:53:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56688 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731602AbgIHQNo (ORCPT ); Tue, 8 Sep 2020 12:13:44 -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 99018C0613ED for ; Tue, 8 Sep 2020 04:37:16 -0700 (PDT) Received: by mail-wr1-x444.google.com with SMTP id c18so18709766wrm.9 for ; Tue, 08 Sep 2020 04:37:16 -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=I/sh0hf7RWpKTkHRG2sXo6X29i3mK1fyatkLVFjwPyY=; b=TRI4o8zL814YHGA/D/zYMJIAaCIYqFZ0mIpUDMLZUZN87cVGkWukeoAQibFqRSdTi0 6pbezBxBfFFSAjRUKWB8QJP5CHgs93NHYtFiS1nIDp648nb0kIv2ZVQ/RTs1fTwlNaec GPg0wCc5jkN3j+ma2gtmxo4nY/EYhDvIrUWKQ= 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=I/sh0hf7RWpKTkHRG2sXo6X29i3mK1fyatkLVFjwPyY=; b=c/ETLbJPQacM2vlW2UMLPGQJCrAKEjSnTuLlJ01/rVCy3i6nOlg1uVJtTiNnBgPwgC 2IC0DdOjNONDAfTjKk8MOo2dHB7hip6fDs2HtbQ2J4Seu/Xa6KxF9jzgoKsbU6QgXmtE IvNAncZBj//L1/iOmpFDDswQQDkVi9Lb0L7PSlGivLqW/AtjA4qrWVPow9Ge5bvY9jCZ fUda7HJlaOARDbxLkK3YBSBD7jQhjN7w/EaEso/2m/rL0R53iy/cVO2b0rA1ZrolGlN1 5FinnYMe9zbzWRTTvJn0xBVE/VJt1EZF9GGUctSGS79HmF2q8RFd1q33VCdIbMJN48BJ TxIQ== X-Gm-Message-State: AOAM530Q+/drS31Z0F+AYLPEy9McBjJDx41pUAFRVufVXjI5wfu8t7GW b1gMoytbCa+8dEttMp4frEg9ZQ== X-Google-Smtp-Source: ABdhPJyF2qwliIvI/LNW3ilYwO975TKwRXyUs29RK60LvcJNYZwaiKnp5x/7ZaLEGFTKwLjPhYZ/og== X-Received: by 2002:adf:fd01:: with SMTP id e1mr24749831wrr.44.1599565035147; Tue, 08 Sep 2020 04:37:15 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id e18sm39103291wra.36.2020.09.08.04.37.13 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 08 Sep 2020 04:37:14 -0700 (PDT) Date: Tue, 8 Sep 2020 13:37:12 +0200 From: Daniel Vetter To: Gerd Hoffmann Cc: dri-devel , Christian =?iso-8859-1?Q?K=F6nig?= , Alex Deucher , David Airlie , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Lucas Stach , Russell King , Christian Gmeiner , Rob Clark , Sean Paul , Ben Skeggs , Sandy Huang , Heiko =?iso-8859-1?Q?St=FCbner?= , Thierry Reding , Jonathan Hunter , Oleksandr Andrushchenko , "open list:RADEON and AMDGPU DRM DRIVERS" , open list , "moderated list:DRM DRIVERS FOR VIVANTE GPU IP" , "open list:DRM DRIVER FOR MSM ADRENO GPU" , "open list:DRM DRIVER FOR MSM ADRENO GPU" , "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" , "moderated list:ARM/Rockchip SoC support" , "open list:ARM/Rockchip SoC support" , "open list:DRM DRIVERS FOR NVIDIA TEGRA" , "moderated list:DRM DRIVERS FOR XEN" Subject: Re: [PATCH v4 1/1] drm: allow limiting the scatter list size. Message-ID: <20200908113712.GL2352366@phenom.ffwll.local> Mail-Followup-To: Gerd Hoffmann , dri-devel , Christian =?iso-8859-1?Q?K=F6nig?= , Alex Deucher , David Airlie , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Lucas Stach , Russell King , Christian Gmeiner , Rob Clark , Sean Paul , Ben Skeggs , Sandy Huang , Heiko =?iso-8859-1?Q?St=FCbner?= , Thierry Reding , Jonathan Hunter , Oleksandr Andrushchenko , "open list:RADEON and AMDGPU DRM DRIVERS" , open list , "moderated list:DRM DRIVERS FOR VIVANTE GPU IP" , "open list:DRM DRIVER FOR MSM ADRENO GPU" , "open list:DRM DRIVER FOR MSM ADRENO GPU" , "open list:DRM DRIVER FOR NVIDIA GEFORCE/QUADRO GPUS" , "moderated list:ARM/Rockchip SoC support" , "open list:ARM/Rockchip SoC support" , "open list:DRM DRIVERS FOR NVIDIA TEGRA" , "moderated list:DRM DRIVERS FOR XEN" References: <20200907112425.15610-1-kraxel@redhat.com> <20200907112425.15610-2-kraxel@redhat.com> <20200908054858.um34wojjv6uhi7d3@sirius.home.kraxel.org> <20200908085544.GI2352366@phenom.ffwll.local> <20200908100253.b22sff23737l77bo@sirius.home.kraxel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200908100253.b22sff23737l77bo@sirius.home.kraxel.org> X-Operating-System: Linux phenom 5.7.0-1-amd64 Sender: linux-tegra-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-tegra@vger.kernel.org On Tue, Sep 08, 2020 at 12:02:53PM +0200, Gerd Hoffmann wrote: > > > > The comments I've found suggest very much not ... Or is that all very > > > > old stuff only that no one cares about anymore? > > > > > > I think these days it is possible to override dma_ops per device, which > > > in turn allows virtio to deal with the quirks without the rest of the > > > kernel knowing about these details. > > > > > > I also think virtio-gpu can drop the virtio_has_dma_quirk() checks, just > > > use the dma api path unconditionally and depend on virtio core having > > > setup dma_ops in a way that it JustWorks[tm]. I'll look into that next. > > > > The comment above vring_use_dma_api() suggests that this has not yet > > happened, that's why I'm asking. > > Hmm, wading through the code, seems it indeed happen yet, even though my > testing didn't show any issues. Probably pure luck because devices and > cpus have the same memory view on x86. Guess I need to try this on > ppc64 to see it actually failing ... > > So dropping the virtio_has_dma_quirk() checks isn't going to fly. > > Using dma_max_mapping_size() should be fine though. It might use a > lower limit than needed for virtio, but it should not break things. Makes sense. On this patch here: Reviewed-by: Daniel Vetter And I guess would be good if virtio pushes a bit more towards using the dma api abstraction fully so we can get rid of these hacks. Virtio feels like a driver that really should be using dma-api and not dig around behind it because "it' makes stuff 0.5% faster" or so, since being virtualized it's already not the king of speed anyway :-) Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch