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Thu, 1 Oct 2026 16:21:22 +0000 Message-ID: Date: Thu, 1 Oct 2026 11:21:18 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 00/14] Add support for a DRM backlight capability Content-Language: en-US To: Maxime Ripard , Xaver Hugl Cc: Thomas Zimmermann , Javier Martinez Canillas , dri-devel@lists.freedesktop.org, harry.wentland@amd.com, Simona Vetter , Alex Deucher , Maarten Lankhorst , David Airlie , amd-gfx@lists.freedesktop.org, "open list:INTEL DRM DISPLAY FOR XE AND I915 DRIVERS" , "open list:INTEL DRM DISPLAY FOR XE AND I915 DRIVERS" , Hans de Goede References: <20260908044035.62093-1-mario.limonciello@amd.com> <32f96551-358b-4874-8fd1-a685b02853e1@amd.com> <08e47991-0d72-471f-9955-0b4ebbcffcdf@suse.de> From: Mario Limonciello In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: CH0PR03CA0181.namprd03.prod.outlook.com (2603:10b6:610:e4::6) To PH8PR12MB6914.namprd12.prod.outlook.com (2603:10b6:510:1cb::21) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR12MB6914:EE_|DS0PR12MB6560:EE_ X-MS-Office365-Filtering-Correlation-Id: 209ced71-47c0-40f7-2405-08df1fd8080b X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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That way, >>> it would always go through the atomic commit path, no matter whether >>> you're on a "legacy" compositor or not. >> >> That could cause stutter. > > Is it really that bad? I mean, it would be only in scenarios where the > legacy API is being used and I would expect it to become the standard > pretty fast anyway, no? > >>> It probably would, but it would create a precedent I'm not really >>> familiar with. Hotplug events are kind of separate because it really is >>> a hardware event most of the time: you get an interrupt, and report it >>> to userspace. And it's largely outside of the properties space (except >>> maybe for things like edid). >> >> If there's any property changes, userspace does need to be notified >> about it. Whether the change is caused by hardware or software doesn't >> matter. > > Yeah, it turns out we already have a precedent for this for HDCP so it's > not too bad I guess. > >>> If we start having the argument that a property changing must trigger a >>> uevent, then it means that we can expect *any* property to do so >> For anything modified outside of the compositor's control, yes. >> >> The client cap avoids needing uevents for the luminance property >> though, since backlight control is exclusive to DRM if the compositor >> supports it. >> >>> "the compositor needs to be in control of it" can apply to many, like >>> color formats, positions, tiling, etc. >> >> If there were other APIs that desktops relied on for controlling color >> formats and similar, we would indeed also need a client cap for those >> things, until definitely all software is ported away from the old API. > > I really think this series should be split. We obviously need to address > this, but it's kind of decoupled from the UAPI itself, and is only > relevant for a small subset of its usage. And yet it's all we talk > about. It'll be easier to merge in chunks and decoupling the legacy API > handling from the new uapi. > > Maxime How would you feel about a (temporary) Kconfig that lets you pick which API to support? This would effectively mean that we can get the new UAPI integrated without worrying about implications for the legacy API. We can then get compositors all lined up to use the the new API and then bikeshed the compat between the two to let us drop the Kconfig.