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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id ADE80C7EE36 for ; Tue, 28 Feb 2023 11:23:45 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id AA8EA10E04F; Tue, 28 Feb 2023 11:23:44 +0000 (UTC) Received: from madras.collabora.co.uk (madras.collabora.co.uk [IPv6:2a00:1098:0:82:1000:25:2eeb:e5ab]) by gabe.freedesktop.org (Postfix) with ESMTPS id 3FB8810E04F for ; Tue, 28 Feb 2023 11:23:42 +0000 (UTC) Received: from [192.168.2.206] (unknown [109.252.117.89]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: dmitry.osipenko) by madras.collabora.co.uk (Postfix) with ESMTPSA id 3B91E6602FDB; Tue, 28 Feb 2023 11:23:40 +0000 (GMT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1677583420; bh=E6qt90GxOfucMcC6bgFlkh6pyweclyl9Mhp2XoIESkc=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=YDjzY7PLJkIFAF01dNDVw8heJ+9gQNPuvtd1JND0dcYRRzev52TSdtMBmSjgnSITw sp/8nV9TKGiIDVvVSAZbZAZWr0AO2dsN6whyLFH3s2YvxRxcSZh70rKnfXX/HK565/ fIq3gJPzie4UGVNTXZnNkawobX78EWBgIzLT6cJYJD22q/inVAqXi2DkqE48Askn38 i1W7Zauiyp+l+NWiuZfd2vYH+sPzeBytqTk6+1kx8r7tVisAazq2A/MCMgxTnuNm0E lq1JEYRnMMLljU2Uy4T0GvJNMxcLNOFKR4iLsWR+EeiY8Z8RQ6HRemD1l0N4rHuc0p SbKdBvJz49nhA== Message-ID: <33f03f9e-4af3-3237-00dc-d79570d9022a@collabora.com> Date: Tue, 28 Feb 2023 14:23:37 +0300 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH] drm/virtio: Add option to disable KMS support Content-Language: en-US To: Javier Martinez Canillas , Gerd Hoffmann , Rob Clark References: <20230224180225.2477641-1-robdclark@gmail.com> <20230227063821.dg2gbjjwcekbxyzw@sirius.home.kraxel.org> <20230228062809.ccyzgnvizh6jidn4@sirius.home.kraxel.org> <87a60yywo0.fsf@minerva.mail-host-address-is-not-set> From: Dmitry Osipenko In-Reply-To: <87a60yywo0.fsf@minerva.mail-host-address-is-not-set> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Rob Clark , open list , dri-devel@lists.freedesktop.org, Gurchetan Singh , Ryan Neph , David Airlie , "open list:VIRTIO GPU DRIVER" Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On 2/28/23 12:19, Javier Martinez Canillas wrote: > Gerd Hoffmann writes: > > Hello Gerd, > >> On Mon, Feb 27, 2023 at 07:40:11AM -0800, Rob Clark wrote: >>> On Sun, Feb 26, 2023 at 10:38 PM Gerd Hoffmann wrote: >>>> On Fri, Feb 24, 2023 at 10:02:24AM -0800, Rob Clark wrote: >>>>> From: Rob Clark >>>>> >>>>> Add a build option to disable modesetting support. This is useful in >>>>> cases where the guest only needs to use the GPU in a headless mode, or >>>>> (such as in the CrOS usage) window surfaces are proxied to a host >>>>> compositor. >>>> Why make that a compile time option? There is a config option for the >>>> number of scanouts (aka virtual displays) a device has. Just set that >>>> to zero (and fix the driver to not consider that configuration an >>>> error). >>> The goal is to not advertise DRIVER_MODESET (and DRIVER_ATOMIC).. I >>> guess that could be done based on whether there are any scanouts, but >>> it would mean making the drm_driver struct non-const. >> Apparently there is a drm_device->driver_features override, >> (amdgpu uses that). The driver could simply drop the DRIVER_MODESET and >> DRIVER_ATOMIC bits in case no scanout is present instead of throwing an >> error. >> >>> And I think it is legitimate to allow the guest to make this choice, >>> regardless of what the host decides to expose, since it is about the >>> ioctl surface area that the guest kernel exposes to guest userspace. >> I think it is a bad idea to make that a compile time option, I'd suggest >> a runtime switch instead, for example a module parameter to ask the >> driver to ignore any scanouts. >> > I don't think there's a need for a new module parameter, there's already > the virtio-gpu 'modeset' module parameter to enable/disable modsetting > and the global 'nomodeset' kernel cmdline parameter to do it for all DRM > drivers. > > Currently, many drivers just fail to probe when 'nomodeset' is present, > but others only disable modsetting but keep the rendering part. In fact, > most DRM only drivers just ignore the 'nomodeset' parameter. IIUC, Rob's main point for having a config option is solely for security reasons. The config option eliminates possibility of accidentally (or intentionally) enabling KMS from software, which is better to have in case of shipping a product (Chromebook) on which multiple teams are working on. -- Best regards, Dmitry