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 988FFC433F5 for ; Mon, 25 Oct 2021 10:45:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7AED960EE9 for ; Mon, 25 Oct 2021 10:45:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230467AbhJYKrq (ORCPT ); Mon, 25 Oct 2021 06:47:46 -0400 Received: from mail.netline.ch ([148.251.143.180]:54250 "EHLO netline-mail3.netline.ch" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229959AbhJYKrm (ORCPT ); Mon, 25 Oct 2021 06:47:42 -0400 Received: from localhost (localhost [127.0.0.1]) by netline-mail3.netline.ch (Postfix) with ESMTP id 3D29420201D; Mon, 25 Oct 2021 12:45:18 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at netline-mail3.netline.ch Received: from netline-mail3.netline.ch ([127.0.0.1]) by localhost (netline-mail3.netline.ch [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 8Zice53EdW5K; Mon, 25 Oct 2021 12:45:17 +0200 (CEST) Received: from thor (24.99.2.85.dynamic.wline.res.cust.swisscom.ch [85.2.99.24]) by netline-mail3.netline.ch (Postfix) with ESMTPA id 8775120201A; Mon, 25 Oct 2021 12:45:17 +0200 (CEST) Received: from [127.0.0.1] by thor with esmtp (Exim 4.95) (envelope-from ) id 1mexTg-000W6M-Nj; Mon, 25 Oct 2021 12:45:16 +0200 Message-ID: <931230b4-1e73-948d-abaf-f1d62ea58239@daenzer.net> Date: Mon, 25 Oct 2021 12:45:16 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Content-Language: en-CA To: Javier Martinez Canillas , =?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> From: =?UTF-8?Q?Michel_D=c3=a4nzer?= Subject: Re: [RFC PATCH] drm/aperture: Add param to disable conflicting framebuffers removal In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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/drm/parameters/, which I suspect doesn't work with the patch as is (due to the 0600 permissions). -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and Xwayland developer