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 570B2C433F5 for ; Wed, 18 May 2022 10:12:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235006AbiERKMs (ORCPT ); Wed, 18 May 2022 06:12:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39596 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234999AbiERKMq (ORCPT ); Wed, 18 May 2022 06:12:46 -0400 Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B0C9211904A; Wed, 18 May 2022 03:12:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1652868764; x=1684404764; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=44H2RKOVvKLIP2tGa0I9hHC2mQIuuan1x5+PNtxV9K8=; b=dS4s8u3NsK2VyVGdtwJikBwlbhNOKWBgBK6qGBgsINUCJ+6rBTxYNfK8 oxSQli7Sq6KQfKHA6q4zOKXmHzPIGxpCqs9LPMcG19jsMcWjge3vJknkQ E/tjuCDjmcIyYitMa7+hY6np0/RQ1bDZBOCad0RsoH2YCgDPd2gcLn2Sv VVtQRRPWvewmYJYQInRN3F+sm8vik1VxfeFDSj4Vomsr1sIep6cRSB1lP GdcdsEkESFmVAD80ifsdPiMPwb/pagSg434bIydEc1tWSGd5zkqXjgTpU lRQ4pBOP41yQOnF4f5vuah/XM+1j8t/fMCUqcmp17jHhhm/F6hjd1vAEd g==; X-IronPort-AV: E=McAfee;i="6400,9594,10350"; a="332213199" X-IronPort-AV: E=Sophos;i="5.91,234,1647327600"; d="scan'208";a="332213199" Received: from orsmga007.jf.intel.com ([10.7.209.58]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2022 03:12:44 -0700 X-IronPort-AV: E=Sophos;i="5.91,234,1647327600"; d="scan'208";a="569385910" Received: from jwasiuki-mobl1.ger.corp.intel.com (HELO localhost) ([10.249.133.47]) by orsmga007-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 May 2022 03:12:35 -0700 From: Jani Nikula To: Hans de Goede , Ben Skeggs , Karol Herbst , Lyude , Daniel Dadap , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Joonas Lahtinen , Rodrigo Vivi , Tvrtko Ursulin , Alex Deucher , Christian =?utf-8?Q?K=C3=B6nig?= , "Pan, Xinhui" , "Rafael J . Wysocki" , Mika Westerberg , Mark Gross , Andy Shevchenko Cc: nouveau@lists.freedesktop.org, Daniel Vetter , David Airlie , intel-gfx , dri-devel@lists.freedesktop.org, amd-gfx@lists.freedesktop.org, Len Brown , linux-acpi@vger.kernel.org, platform-driver-x86@vger.kernel.org Subject: Re: [PATCH 00/14] drm/kms: Stop registering multiple /sys/class/backlight devs for a single display In-Reply-To: <614a7cef-bfe6-c631-dc4c-d9e99a0b0937@redhat.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo References: <20220517152331.16217-1-hdegoede@redhat.com> <871qwrfcwr.fsf@intel.com> <614a7cef-bfe6-c631-dc4c-d9e99a0b0937@redhat.com> Date: Wed, 18 May 2022 13:12:33 +0300 Message-ID: <87r14rdu9a.fsf@intel.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-acpi@vger.kernel.org On Wed, 18 May 2022, Hans de Goede wrote: > Hi, > > On 5/18/22 10:44, Jani Nikula wrote: >> On Tue, 17 May 2022, Hans de Goede wrote: >>> Hi All, >>> >>> As mentioned in my RFC titled "drm/kms: control display brightness through >>> drm_connector properties": >>> https://lore.kernel.org/dri-devel/0d188965-d809-81b5-74ce-7d30c49fee2d@redhat.com/ >>> >>> The first step towards this is to deal with some existing technical debt >>> in backlight handling on x86/ACPI boards, specifically we need to stop >>> registering multiple /sys/class/backlight devs for a single display. >> >> I guess my question here is, how do you know it's for a *single* >> display? >> >> There are already designs out there with two flat panels, with >> independent brightness controls. They're still rare and I don't think we >> handle them very well. But we've got code to register multiple native >> backlight interfaces, see e.g. commit 20f85ef89d94 ("drm/i915/backlight: >> use unique backlight device names"). >> >> So imagine a design where one of the panels needs backlight control via >> ACPI and the other via native backlight control. Granted, I don't know >> if one exists, but I think it's very much in the realm of possible >> things the OEMs might do. For example, have an EC PWM for primary panel >> backlight, and use GPU PWM for secondary. How do you know you actually >> do need to register two interfaces? > > On x86/ACPI devices this is all driven by acpi_video_get_backlight_type() / > by the drivers/acpi/video_detect.c code. That code already will break on > systems where there are 2 backlight controls, with one being ACPI based > and the other a native GPU PWM backlight device. > > In this scenario as soon as the native GPU PWM backlight device shows up > then, if acpi_video_get_backlight_type()==native, video_detect.c will > currently unregister the acpi_video# backlight device(s) since userspace > prefers the firmware type over the native type, so for userspace to > actually honor the acpi_video_get_backlight_type()==native we need to get > the acpi_video# backlight device "out of the way" which is currently > handled by unregistering it. > > Note in a way we already have a case where userspace sees 2 panels, > in hybrid laptop setups with a mux and on those systems we may see > either 2 native backlight devices; or 2 native backlight devices + > 2 acpi_video backlight devices with userspace preferring the ACPI > ones. > > Also note that userspace already has code to detect if the related > panel is active (iow which way the mux between the GPU and the panels > points) and then uses that backlight device. Userspace here very > much assumes a single panel though. > >> I'm fine with dealing with such cases as they arise to avoid >> over-engineering up front, but I also don't want us to completely paint >> ourselves in a corner either. > > Right. Note that the current code (both with and without this patchset) > already will work fine from a kernel pov as long as both panels > are either using native GPU PWM or are both using ACPI. But if we > ever get a mix then this will need special handling. > > Note that all userspace code I know is currently hardcoded > to assume a single panel. Userspace already picks one preferred > device under /sys/class/backlight and ignores the rest. Actually > atm userspace must behave this way, because on x86/ACPI boards we > do often register multiple backlight devices for a single panel. > > So in a way moving to registering only a single backlight device > prepares for actually having multiple panels work. > > Also keep in mind that this is preparation work for making the > panel brightness a drm_connector property. When the panel uses > a backlight device other then the native GPU PWM to control the > brightness then the helper code for this needs to have a way to > select which backlight_device to use then and the non native > types are not "linked" to a specific connector so in this case > we really need there to be only 1 backlight device registered > so that the code looking up the (non native) backlight device > for the connector gets the right one and not merely the one > which happened to get registered first. > > And I believe that having the panel brightness be a drm_connector > property is the way to make it possible for userspace to deal > with the multiple panels which each have a separate brightness > control case. Agreed. Thanks for the explanations and recording them here. BR, Jani. > > Regards, > > Hans > > > > > >> >> BR, >> Jani. >> >> >>> >>> This series implements my RFC describing my plan for these cleanups: >>> https://lore.kernel.org/dri-devel/98519ba0-7f18-201a-ea34-652f50343158@redhat.com/ >>> >>> Specifically patches 1-6 implement the "Fixing kms driver unconditionally >>> register their "native" backlight dev" part. >>> >>> And patches 7-14 implement the "Fixing acpi_video0 getting registered for >>> a brief time" time. >>> >>> Note this series does not deal yet with the "Other issues" part, I plan >>> to do a follow up series for that. >>> >>> The changes in this series are good to have regardless of the further >>> "drm/kms: control display brightness through drm_connector properties" >>> plans. So I plan to push these upstream once they are ready (once >>> reviewed). Since this crosses various subsystems / touches multiple >>> kms drivers my plan is to provide an immutable branch based on say >>> 5.19-rc1 and then have that get merged into all the relevant trees. >>> >>> Please review. >>> >>> Regards, >>> >>> Hans >>> >>> >>> Hans de Goede (14): >>> ACPI: video: Add a native function parameter to >>> acpi_video_get_backlight_type() >>> drm/i915: Don't register backlight when another backlight should be >>> used >>> drm/amdgpu: Don't register backlight when another backlight should be >>> used >>> drm/radeon: Don't register backlight when another backlight should be >>> used >>> drm/nouveau: Don't register backlight when another backlight should be >>> used >>> ACPI: video: Drop backlight_device_get_by_type() call from >>> acpi_video_get_backlight_type() >>> ACPI: video: Remove acpi_video_bus from list before tearing it down >>> ACPI: video: Simplify acpi_video_unregister_backlight() >>> ACPI: video: Make backlight class device registration a separate step >>> ACPI: video: Remove code to unregister acpi_video backlight when a >>> native backlight registers >>> drm/i915: Call acpi_video_register_backlight() >>> drm/nouveau: Register ACPI video backlight when nv_backlight >>> registration fails >>> drm/amdgpu: Register ACPI video backlight when skipping amdgpu >>> backlight registration >>> drm/radeon: Register ACPI video backlight when skipping radeon >>> backlight registration >>> >>> drivers/acpi/acpi_video.c | 69 ++++++++++++++----- >>> drivers/acpi/video_detect.c | 53 +++----------- >>> drivers/gpu/drm/Kconfig | 2 + >>> .../gpu/drm/amd/amdgpu/atombios_encoders.c | 14 +++- >>> .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 9 +++ >>> .../gpu/drm/i915/display/intel_backlight.c | 7 ++ >>> drivers/gpu/drm/i915/display/intel_display.c | 1 + >>> drivers/gpu/drm/i915/display/intel_opregion.c | 2 +- >>> drivers/gpu/drm/nouveau/nouveau_backlight.c | 14 ++++ >>> drivers/gpu/drm/radeon/atombios_encoders.c | 7 ++ >>> drivers/gpu/drm/radeon/radeon_encoders.c | 11 ++- >>> .../gpu/drm/radeon/radeon_legacy_encoders.c | 7 ++ >>> drivers/platform/x86/acer-wmi.c | 2 +- >>> drivers/platform/x86/asus-laptop.c | 2 +- >>> drivers/platform/x86/asus-wmi.c | 4 +- >>> drivers/platform/x86/compal-laptop.c | 2 +- >>> drivers/platform/x86/dell/dell-laptop.c | 2 +- >>> drivers/platform/x86/eeepc-laptop.c | 2 +- >>> drivers/platform/x86/fujitsu-laptop.c | 4 +- >>> drivers/platform/x86/ideapad-laptop.c | 2 +- >>> drivers/platform/x86/intel/oaktrail.c | 2 +- >>> drivers/platform/x86/msi-laptop.c | 2 +- >>> drivers/platform/x86/msi-wmi.c | 2 +- >>> drivers/platform/x86/samsung-laptop.c | 2 +- >>> drivers/platform/x86/sony-laptop.c | 2 +- >>> drivers/platform/x86/thinkpad_acpi.c | 4 +- >>> drivers/platform/x86/toshiba_acpi.c | 2 +- >>> include/acpi/video.h | 8 ++- >>> 28 files changed, 156 insertions(+), 84 deletions(-) >> > -- Jani Nikula, Intel Open Source Graphics Center