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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 120ECFA3740 for ; Tue, 25 Oct 2022 19:33:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231629AbiJYTdE (ORCPT ); Tue, 25 Oct 2022 15:33:04 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231193AbiJYTdE (ORCPT ); Tue, 25 Oct 2022 15:33:04 -0400 Received: from cavan.codon.org.uk (irc.codon.org.uk [IPv6:2a00:1098:84:22e::2]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F1944DBE77; Tue, 25 Oct 2022 12:32:51 -0700 (PDT) Received: by cavan.codon.org.uk (Postfix, from userid 1000) id 6C71B4245C; Tue, 25 Oct 2022 20:32:48 +0100 (BST) Date: Tue, 25 Oct 2022 20:32:48 +0100 From: Matthew Garrett To: Hans de Goede Cc: Dmitry Osipenko , Ben Skeggs , Karol Herbst , Lyude , Daniel Dadap , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Alex Deucher , Christian =?iso-8859-1?Q?K=F6nig?= , Pan@freedesktop.org, Xinhui , "Rafael J . Wysocki" , Mika Westerberg , Lukas Wunner , Mark Gross , Andy Shevchenko , linux-acpi@vger.kernel.org, Jani Nikula , nouveau@lists.freedesktop.org, intel-gfx , dri-devel@lists.freedesktop.org, platform-driver-x86@vger.kernel.org, amd-gfx@lists.freedesktop.org, David Airlie , Len Brown Subject: Re: [PATCH v5 02/31] drm/i915: Don't register backlight when another backlight should be used (v2) Message-ID: <20221025193248.GA21457@srcf.ucam.org> References: <20220825143726.269890-1-hdegoede@redhat.com> <20220825143726.269890-3-hdegoede@redhat.com> <42a5f2c9-a1dc-8fc0-7334-fe6c390ecfbb@redhat.com> <20221024203057.GA28675@srcf.ucam.org> <8f53b8b6-ead2-22f5-16f7-65b31f7cc05c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8f53b8b6-ead2-22f5-16f7-65b31f7cc05c@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Tue, Oct 25, 2022 at 08:50:54PM +0200, Hans de Goede wrote: > That is a valid point, but keep in mind that this is only used on ACPI > platforms and then only on devices with a builtin LCD panel and then > only by GPU drivers which actually call acpi_video_get_backlight_type(), > so e.g. not by all the ARM specific display drivers. > > So I believe that Chromebooks quite likely are the only devices with > this issue. My laptop is, uh, weird, but it falls into this category. > > I think for this to work correctly you need to have > > the infrastructure be aware of whether or not a vendor interface exists, > > which means having to handle cleanup if a vendor-specific module gets > > loaded later. > > Getting rid of the whole ping-ponging of which backlight drivers > get loaded during boot was actually one of the goals of the rework > which landed in 6.1 this actually allowed us to remove some quirks > because some hw/firmware did not like us changing our mind and > switching backlight interfaces after first poking another one. > So we definitely don't want to go back to the ping-pong thing. Defaulting to native but then having a vendor driver be able to disable native drivers seems easiest? It shouldn't be a regression over the previous state of affairs since both drivers were being loaded already.