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 X-Spam-Level: X-Spam-Status: No, score=-7.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6E868C43331 for ; Mon, 30 Mar 2020 20:51:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 448F7206CC for ; Mon, 30 Mar 2020 20:51:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QfSq6X/t" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728405AbgC3UvM (ORCPT ); Mon, 30 Mar 2020 16:51:12 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:37471 "EHLO us-smtp-delivery-74.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727750AbgC3UvM (ORCPT ); Mon, 30 Mar 2020 16:51:12 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585601471; 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=odm2BtAQUnUT8zj+digzS3rtXLQBUeiDF1C1EBhIhHQ=; b=QfSq6X/thgqU5NJsRNEqMJKHrkswmWyeoeiBqulcLT2hHSYzw0y+gh0tJ6T3RGuFxKMHre +sBnc+ovoPgIOjD1usTpgGZzyNuNCXpTL0m8n+jBK705xuPPVX6M3u63l02vmilae/GK2y iGM5MEEJiScMX07f+d0ECvAOS9c1IRY= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-188-WOT0WHtPMbmE89W4wMcRwg-1; Mon, 30 Mar 2020 16:51:04 -0400 X-MC-Unique: WOT0WHtPMbmE89W4wMcRwg-1 Received: by mail-wr1-f70.google.com with SMTP id w12so11884990wrl.23 for ; Mon, 30 Mar 2020 13:51:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=odm2BtAQUnUT8zj+digzS3rtXLQBUeiDF1C1EBhIhHQ=; b=TG3FT9Fn2ICfeZjyBFirm8RWKPtNslG65YR3Ry9VSJgRS6JwqqAJR6LvhDZfJK6JcR S4AXzY1MDQwdBESNJ2XAqLWuzI7uFRc24YjWMV4Y9xzcvhr5d0EYVbzg9JCD75yl4fIM ay+I8nKd32Vy4D8u6OfZvDX8K0swU/ioGv0e4xuB88UcbYrnbQuT+0mlgW2g9o1LXpPi G/hIZO9NFte7vk5nXiRcn76CHNywLkMHLwdfpn8u5pYQ3GEFvPcr3nFj/Umxr7Q/RoaW Vn7gRykDCiihoq2wACKBXuacLPS5ykZZgeilzHXO+Mavw9jLt54o1gjAi0dFCGSBxmWM xFCA== X-Gm-Message-State: ANhLgQ0mbs+DLzPf9Lf7IhO2e2rBoXS5E+z0oTDLwHNw7U98+DnqxCLo mL0rd71DSfQ8cPZl2fFrX/4p7BfIaq+DvmF5+mjPl+Qaz5gk4+Wgl7Y/WuCVFav7+Mh4RC6RWY4 r2F7cuFm2EdtCjeQ0XIPGYA== X-Received: by 2002:adf:bb4c:: with SMTP id x12mr16140813wrg.137.1585601462962; Mon, 30 Mar 2020 13:51:02 -0700 (PDT) X-Google-Smtp-Source: ADFU+vsivJs4jCKEDqtzyiapgH6FhTN+YcSjT2DE+4y/sRoMwbXGG618EuuJZHiMOPUt0GsirQs3Yw== X-Received: by 2002:adf:bb4c:: with SMTP id x12mr16140799wrg.137.1585601462755; Mon, 30 Mar 2020 13:51:02 -0700 (PDT) Received: from x1.localdomain (2001-1c00-0c0c-fe00-fc7e-fd47-85c1-1ab3.cable.dynamic.v6.ziggo.nl. [2001:1c00:c0c:fe00:fc7e:fd47:85c1:1ab3]) by smtp.gmail.com with ESMTPSA id g128sm916407wmf.27.2020.03.30.13.51.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 30 Mar 2020 13:51:02 -0700 (PDT) Subject: Re: ACPI Video Driver creates backlight on desktop board To: Paul Menzel , Zhang Rui Cc: linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org References: <75866748-f574-ae50-6183-ef6892c935c5@molgen.mpg.de> From: Hans de Goede Message-ID: <63956e11-46f2-72f4-c722-8fee2cbfbfa1@redhat.com> Date: Mon, 30 Mar 2020 22:51:01 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <75866748-f574-ae50-6183-ef6892c935c5@molgen.mpg.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-acpi-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org Hi, On 3/29/20 11:36 AM, Paul Menzel wrote: > Dear Linux folks, > > > On the MSI desktop board [1] > >     [    0.000000] DMI: Micro-Star International Co., Ltd. MS-7A37/B350M MORTAR (MS-7A37), BIOS 1.MR 12/02/2019 > > with an AMD Ryzen 3 2200G with Radeon Vega Graphics, the ACPI Video Driver `video` is loaded and creates a backlight device. > >     $ readlink -f /sys/class/backlight/acpi_video0 >     /sys/devices/pci0000:00/0000:00:08.1/0000:26:00.0/backlight/acpi_video0 > > I wonder what the driver is used for as the AMDGPU driver exists for the graphics device. Backlight on x86 hw is a bit of a mess, there is an ACPI standard for accessing it and with older (Windows XP era) laptops that is the interface which usually works, then there are a bunch of vendor specific SMBIOS or WMI backlight interfaces and then there is the option of directly accessing the hardware as the amdgpu driver is doing. We have a bunch of heuristics to avoid the acpi_video driver registering a backlight interface when it should not, either because the direct hw access should be used instead; or because there simply is no builtin LCD panel and thus no backlight to control. These heuristics are failing on your board. > If it’s useful, is there a way to prevent the backlight interface from getting created? You can pass "acpi_backlight=ignore" on the kernel commandline to disable the interface, this will stop e.g. gnome from showing a non working brightness slider in its top right system menu. If this works you can make this permanent and avoid other users from having to do the same thing by writing a patch adding a quirk for this like this one: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d21a91629f4b8e794fc4c0e0c17c85cedf1d806c Regards, Hans