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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7ED16C433F5 for ; Mon, 25 Oct 2021 12:29:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5FA4F60EE9 for ; Mon, 25 Oct 2021 12:29:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233083AbhJYMbY (ORCPT ); Mon, 25 Oct 2021 08:31:24 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:51072 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232582AbhJYMbW (ORCPT ); Mon, 25 Oct 2021 08:31:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1635164939; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=2ODWAC2kPVBIFuPUdtI4g09Ho4gCD2YMuSiOZS86l4U=; b=BndqNhHCvJ+Glm6IdujH4+o0KOyKLXRozmf/zNWWSyYQdpmUg373vahWncCMQOakut0fB5 ZbsQWxIRP/zTocR0MengVjc6yEIK6vYJp31/0eoGnPgTOHGOE92K5CScxGSaTCwpL4M/Nk hCIfb/w4cK9CKBCtyF5r50zCVXSsbLg= Received: from mail-wm1-f70.google.com (mail-wm1-f70.google.com [209.85.128.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-415-qwxBnBBsMFKoWto3aWCFmA-1; Mon, 25 Oct 2021 08:28:57 -0400 X-MC-Unique: qwxBnBBsMFKoWto3aWCFmA-1 Received: by mail-wm1-f70.google.com with SMTP id z17-20020a7bc7d1000000b0032cafafaf79so1928090wmk.5 for ; Mon, 25 Oct 2021 05:28:57 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=2ODWAC2kPVBIFuPUdtI4g09Ho4gCD2YMuSiOZS86l4U=; b=aOfwO9AdbGtvHxs/FtB26mu9kB2rkUDcRe/wnwCgLS/71pxaX4n2sEwB+p2lPcfmGO gYR7wBnztDdpDmu4czlav1pS+zJzkkmeXXNfBuP9f/aNa9QXQMIsHJn0BqBoy8U/KmLm Ohax5lORE+uQQaKN9rQ4GJ8M5/p1j3gIbVnR3UNX5AukXmxO7PbNGhsqhxzkTpuurYNx mkQzP0MwtvKX2FBH5RfdYWFu+vyq+tUofniqpuJT4vlFzrfpMKcW48B0lgAqCaUNkVFp 6/hEHed+77FZW+aMMJd3/jBFzEntvL8g/EfKbtpRTBt5pC9lk1rp/rC/5hQFnLl+Kdh1 nZTA== X-Gm-Message-State: AOAM532F5WSOczEGkwZPxoad0Cni2CJSlS0mXq8cm90wpD0atoBQemyz EayPA6vX6v6O8SScZhwEHq6ci4Rjb3p01xC/pd9iQkVwZt36YwYVt6sGaN0fJ/0cNPsAgOEM/rf qVbAowAa4xm2iAzkd0fwxXvYM X-Received: by 2002:a5d:62d0:: with SMTP id o16mr23263782wrv.206.1635164936543; Mon, 25 Oct 2021 05:28:56 -0700 (PDT) X-Google-Smtp-Source: ABdhPJw617Ej0Qgn2OshjIK1/cSPxPzf4Dx4RNMcL9U1rlmQG2vOOyYfwwjD+PbnuD24/smsnfHsBQ== X-Received: by 2002:a5d:62d0:: with SMTP id o16mr23263752wrv.206.1635164936232; Mon, 25 Oct 2021 05:28:56 -0700 (PDT) Received: from [192.168.1.128] ([92.176.231.106]) by smtp.gmail.com with ESMTPSA id b19sm19153070wmj.9.2021.10.25.05.28.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 25 Oct 2021 05:28:55 -0700 (PDT) Message-ID: Date: Mon, 25 Oct 2021 14:28:54 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [RFC PATCH] drm/aperture: Add param to disable conflicting framebuffers removal Content-Language: en-US To: =?UTF-8?Q?Michel_D=c3=a4nzer?= , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= Cc: linux-kernel@vger.kernel.org, Thomas Zimmermann , Peter Robinson , Neal Gompa , Daniel Vetter , David Airlie , Maarten Lankhorst , Maxime Ripard , dri-devel@lists.freedesktop.org References: <20211022144040.3418284-1-javierm@redhat.com> <931230b4-1e73-948d-abaf-f1d62ea58239@daenzer.net> From: Javier Martinez Canillas In-Reply-To: <931230b4-1e73-948d-abaf-f1d62ea58239@daenzer.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello Michel, On 10/25/21 12:45, Michel Dänzer wrote: > On 2021-10-24 22:32, Javier Martinez Canillas wrote: >> Hello Ville, >> >> On 10/22/21 21:12, Ville Syrjälä wrote: >>> On Fri, Oct 22, 2021 at 04:40:40PM +0200, Javier Martinez Canillas wrote: >>>> The simpledrm driver allows to use the frame buffer that was set-up by the >>>> firmware. This gives early video output before the platform DRM driver is >>>> probed and takes over. >>>> >>>> But it would be useful to have a way to disable this take over by the real >>>> DRM drivers. For example, there may be bugs in the DRM drivers that could >>>> cause the display output to not work correctly. >>>> >>>> For those cases, it would be good to keep the simpledrm driver instead and >>>> at least get a working display as set-up by the firmware. >>>> >>>> Let's add a drm.remove_fb boolean kernel command line parameter, that when >>>> set to false will prevent the conflicting framebuffers to being removed. >>>> >>>> Since the drivers call drm_aperture_remove_conflicting_framebuffers() very >>>> early in their probe callback, this will cause the drivers' probe to fail. >>> >>> Why is that better than just modprobe.blacklisting those drivers? >> >> Because would allow to deny list all native (as Thomas called it) DRM drivers >> and only allow the simpledrm driver to be probed. This is useful for distros, >> since could add a "Basic graphics mode" to the boot menu entries, that could >> boot the kernel passing a "drm.disable_native_drivers=1" cmdline option. >> >> That way, if there's any problem with a given DRM driver, the distro may be >> installed and booted using the simpledrm driver and troubleshoot why a native >> DRM driver is not working. Or try updating the kernel package, etc. > > For troubleshooting, it'll be helpful if this new parameter can be enabled for the boot via the kernel command line, then disabled again after boot-up. One simple possibility for this would be allowing the parameter to be changed via /sys/module That's already the case with the current patch, i.e: $ grep -o drm.* /proc/cmdline drm.disable_native_drivers=1 $ cat /proc/fb 0 simpledrm $ modprobe virtio_gpu $ dmesg [ 125.731549] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 125.732410] virtio_gpu: probe of virtio0 failed with error -16 $ echo 0 > /sys/module/drm/parameters/disable_native_drivers $ modprobe virtio_gpu $ dmesg [ 187.889136] [drm] pci: virtio-vga detected at 0000:00:01.0 [ 187.894578] Console: switching to colour dummy device 80x25 [ 187.897090] virtio-pci 0000:00:01.0: vgaarb: deactivate vga console [ 187.899983] [drm] features: -virgl +edid -resource_blob -host_visible [ 187.907176] [drm] number of scanouts: 1 [ 187.907714] [drm] number of cap sets: 0 [ 187.914108] [drm] Initialized virtio_gpu 0.1.0 0 for virtio0 on minor 1 [ 187.930807] Console: switching to colour frame buffer device 128x48 [ 187.938737] virtio_gpu virtio0: [drm] fb0: virtio_gpu frame buffer device $ cat /proc/fb 0 virtio_gpu /drm/parameters/, which I suspect doesn't work with the patch as is (due to the 0600 permissions). > > I followed the convention used by other drm module parameters, hence the 0600. Do you mean that for this parameter we should be less restrictive ? Best regards, -- Javier Martinez Canillas Linux Engineering Red Hat