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Fri, 14 Nov 2025 19:17:28 +0000 Message-ID: Date: Fri, 14 Nov 2025 13:17:25 -0600 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/amd: Move adaptive backlight modulation property to drm core To: Jani Nikula , Simona Vetter , xaver.hugl@kde.org Cc: Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , David Airlie , "open list:RADEON and AMDGPU DRM DRIVERS" , "open list:DRM DRIVERS" , open list , Simona Vetter , Harry Wentland , Dmitry Baryshkov , Thomas Zimmermann , Maxime Ripard References: <20251112222646.495189-1-mario.limonciello@amd.com> <83aa8a816cf301085a3e3638238f8fba11053dc2@intel.com> <449ee5ba065e1ceee8f7a04038442cff24772df9@intel.com> Content-Language: en-US From: Mario Limonciello In-Reply-To: <449ee5ba065e1ceee8f7a04038442cff24772df9@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SA1PR05CA0005.namprd05.prod.outlook.com (2603:10b6:806:2d2::7) To MN0PR12MB6101.namprd12.prod.outlook.com (2603:10b6:208:3cb::10) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: MN0PR12MB6101:EE_|DS0PR12MB9726:EE_ X-MS-Office365-Filtering-Correlation-Id: 91a8c605-a007-48c3-4aa3-08de23b27368 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|366016|7416014|376014; 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Seriously suggesting that to the common ABI? We shouldn't have >> sysfs involved at all, let alone vendor specific sysfs. >> >>> + * off >>> + * Adaptive backlight modulation is disabled. >>> + * min >>> + * Adaptive backlight modulation is enabled at minimum intensity. >>> + * bias min >>> + * Adaptive backlight modulation is enabled at a more intense >>> + * level than 'min'. >>> + * bias max >>> + * Adaptive backlight modulation is enabled at a more intense >>> + * level than 'bias min'. >>> + * max >>> + * Adaptive backlight modulation is enabled at maximum intensity. >> >> So values 0-4 but with names. I don't know what "bias" means here, and I >> probably shouldn't even have to know. It's an implementation detail >> leaking to the ABI. >> >> In the past I've encountered CABC with different modes based on the use >> case, e.g. "video" or "game", but I don't know how those would map to >> the intensities. >> >> I'm concerned the ABI serves AMD hardware, no one else, and everyone >> else coming after this is forced to shoehorn their implementation into >> this. > > Apparently Harry had the same concerns [1]. > So let me explain how we got here. At the display next hackfest last year (2024) we talked about how to get compositors to indicate they want technologies like this to get out the way. A patch series was made that would allow compositor to say "Require color accuracy" or "Require low latency" are required. https://lore.kernel.org/amd-gfx/20240703051722.328-1-mario.limonciello@amd.com/ This got reverted because userspace didn't have an implementation ready to go at the time. One was created and so I rebased/resent the series earlier this year. https://lore.kernel.org/amd-gfx/20250621152657.1048807-1-superm1@kernel.org/ Xaver had some change of heart and wanted to talk about it at the next hackfest. https://lore.kernel.org/amd-gfx/CAFZQkGxUwodf5bW0qQkXoPoz0CFFA1asJfUxFftMGgs5-VK2Hw@mail.gmail.com/ So we talked about it again at the hackfest this year and the decision was not everyone can an octagon into a peg hole, so we're better off re-introducing vendor properties for this. So series was respun per that discussion. https://lore.kernel.org/amd-gfx/20250718192045.2091650-1-superm1@kernel.org/ Userspace implementation was done and so we merged this for 6.19. https://lore.kernel.org/amd-gfx/CAFZQkGwLWcyS0SqCHoiGsJd5J_u4aBJ0HMV5Bx3NknLdLkr8Uw@mail.gmail.com/ Then Simona suggested we need to make some changes where the propertye should be in generic documentation etc: https://lore.kernel.org/amd-gfx/aQUz-mbM_WlXn_uZ@phenom.ffwll.local/ So that's where we are now with this patch. I can clean it up per the feedback so far - but I think we need to be in agreement that this property is actually the way forward or we should revert the property in amdgpu instead of this moving approach and keep discussing.