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 DDD85C38A2D for ; Thu, 27 Oct 2022 09:52:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234815AbiJ0Jwy (ORCPT ); Thu, 27 Oct 2022 05:52:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34022 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234886AbiJ0Jww (ORCPT ); Thu, 27 Oct 2022 05:52:52 -0400 Received: from cavan.codon.org.uk (cavan.codon.org.uk [176.126.240.207]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1A331DCAFB; Thu, 27 Oct 2022 02:52:50 -0700 (PDT) Received: by cavan.codon.org.uk (Postfix, from userid 1000) id 841D440A8B; Thu, 27 Oct 2022 10:52:49 +0100 (BST) Date: Thu, 27 Oct 2022 10:52:49 +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?= , 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: <20221027095249.GA28666@srcf.ucam.org> References: <20221025193248.GA21457@srcf.ucam.org> <144cd47e-42dc-2b84-1a90-ea5e080e08a3@redhat.com> <20221025204043.GA23306@srcf.ucam.org> <20221025234040.GA27673@srcf.ucam.org> <20221026204920.GA15326@srcf.ucam.org> <099dee98-8aeb-af36-828c-110f5ac6e9a3@redhat.com> <20221027091123.GA28089@srcf.ucam.org> <933be908-0bc2-56cc-8d6f-38f2d208ef20@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <933be908-0bc2-56cc-8d6f-38f2d208ef20@redhat.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Thu, Oct 27, 2022 at 11:39:38AM +0200, Hans de Goede wrote: > The *only* behavior which actually is new in 6.1 is the native GPU > drivers now doing the equivalent of: > > if (acpi_video_get_backlight_type() != acpi_backlight_native) > return; > > In their backlight register paths (i), which is causing the native > backlight to disappear on your custom laptop setup and on Chromebooks > (with the Chromebooks case being already solved I hope.). It's causing the backlight control to vanish on any machine that isn't ((acpi_video || vendor interface) || !acpi). Most machines that fall into that are either weird or Chromebooks or old, but there are machines that fall into that. (I wrote https://mjg59.livejournal.com/127103.html over 12 years ago, so please do assume that I'm familiar with the complexities here :) ) > I agree this is a possible solution if this turns out to break more > systems and there is no other easy/clean way to fix those. But I would > greatly prefer to keep this change and stop the IMHO bad kernel behavior > of "registering multiple backlight-devices for a single panel and then > let userspace sort it out". If we're not able to make a correct policy decision in the kernel then punting it to userland seems like the right thing to do? The kernel absolutely *should* make the right decision where it has enough information to do so, but in this case the code that's making that decision doesn't have the full set of information.