From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from BL0PR03CU003.outbound.protection.outlook.com (mail-eastusazon11012034.outbound.protection.outlook.com [52.101.53.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E125C30BF4E for ; Thu, 2 Apr 2026 17:07:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=fail smtp.client-ip=52.101.53.34 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775149636; cv=fail; b=pAEtuFHPoVjGqJrmDyLxJcRGHdgPfOiuZWzaHPZ7yXr9y1fS9pFRrFjvZjmDcg/LuTeHj61YaC1QHV4c6wWkSoxcfUj1z6AyjLSmALrYWFPUjXxUD09ht/hfvp21yyAvMS6s4GeRRSmaZQYPZbwOcWoIGHy1sgxy4LGfye1tqbY= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775149636; c=relaxed/simple; bh=lZ2wZx1sMK6nWiRclBVDgUQ52qxu534wTCDTM3nj8Ic=; h=Message-ID:Date:Subject:To:Cc:References:From:In-Reply-To: Content-Type:MIME-Version; b=POw53AqzIaMPsQ2W6+hTfjPJFFQMXpl8AXB8MtWBo9K0QgCwALTlBS2lU6mgPcyNlsZetJZRH25kK3Bh/FIEuhDaoelEYO7NycCLlBbbDXF1xCuTeMRARHosDAjRX2AkvmkCaZEa6aYmpyYPG64UeFBrtytAN9/MZ+AWtmfTpxs= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com; spf=fail smtp.mailfrom=amd.com; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b=g5LcPuvn; arc=fail smtp.client-ip=52.101.53.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=amd.com Authentication-Results: smtp.subspace.kernel.org; spf=fail smtp.mailfrom=amd.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=amd.com header.i=@amd.com header.b="g5LcPuvn" ARC-Seal: i=1; a=rsa-sha256; s=arcselector10001; d=microsoft.com; cv=none; b=CDnjqIvfUtSzkWI/Na1/qFUX5prgAeZyb1icAxmluC46ZyVumum/oXT25vsBBaTUcGWNHHjmA1gorh2h9Hu8t4T6yhylyBbXtsGytBY53xGqDxr5D/GgI72MDLA6EaAB66dPbDacAdrqWyPo7SOFmkw2EB7PI2V8/G0JrOt/5cK+1VOKcGafetZHkIl5Q8VXEzc42N9fqWKXDJNo+JR13EBFe4C1+9Vj83C5xOMUuIH3SlQtMlaHeKYliQim3OXonfNqxzfe+n4xJB2pxHga1GbBHSD0W29XiT+PojRbGwxaZAB0q+2CJpOr42DhRu0erZoGiFJJ3dtYu0h+TR/p6A== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=microsoft.com; s=arcselector10001; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-AntiSpam-MessageData-ChunkCount:X-MS-Exchange-AntiSpam-MessageData-0:X-MS-Exchange-AntiSpam-MessageData-1; bh=K0XFe0xYiHgY0UWVxiokllC/RLbV31em7iWm2THFRAs=; b=qglp+TFd1uL4sVCnMImcs4V/+p80A2hlHCwQDC4FsdSUnDAGQ6ywL1buJgVjluVC/Y5sa75D9ULZe+amIUVlu3ckH/fyXmltLzdTOdi8XDkHE4Anf+dcy5i4pNHBrrMns0DWBwH9Ly5YnA8zjylZGQ52WheaAJVaEzBk4y+Hbij24rranJ3khETYV0Qsjf58n8JjAmTxn8nFtsCtkYqK6oSKWwyCAcnP6coRCVwTSsTt9GIYW4pX7VUs8KPZ94E/rktAfrcMHBV9ZQBnX8XE1ncRQMOWdGbXRC2eCDUYhbifBBWtc18kZ0HbXOCxPWJvjsH29wIpCrijYnHcsFeq7A== ARC-Authentication-Results: i=1; mx.microsoft.com 1; spf=pass smtp.mailfrom=amd.com; dmarc=pass action=none header.from=amd.com; dkim=pass header.d=amd.com; arc=none DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amd.com; s=selector1; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=K0XFe0xYiHgY0UWVxiokllC/RLbV31em7iWm2THFRAs=; b=g5LcPuvnCCCeVqaWRv70XrMhZNuWNjSfVXtGAIy/2ox4O43sIIgaIwyYqPfgIUsu/EJtSqgRjjgA7rSeQ2wFMTcnlcdyo+Pok1ItReD+2f+dsD/5mJpSBYdvpugbHLJOnkzyUw3M0KLYadjJZyrzN7Ka2TbpZilSFM0F6b4MOFM= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from BL1PR12MB5126.namprd12.prod.outlook.com (2603:10b6:208:312::8) by MW4PR12MB6897.namprd12.prod.outlook.com (2603:10b6:303:20a::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.9769.17; Thu, 2 Apr 2026 17:07:04 +0000 Received: from BL1PR12MB5126.namprd12.prod.outlook.com ([fe80::c3e7:1bc5:2b91:1cfe]) by BL1PR12MB5126.namprd12.prod.outlook.com ([fe80::c3e7:1bc5:2b91:1cfe%5]) with mapi id 15.20.9769.020; Thu, 2 Apr 2026 17:07:04 +0000 Message-ID: Date: Thu, 2 Apr 2026 13:06:57 -0400 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 0/3] Add "link bpc" DRM property To: Nicolas Frattaroli , Daniel Stone Cc: Pekka Paalanen , =?UTF-8?Q?Michel_D=C3=A4nzer?= , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Leo Li , Rodrigo Siqueira , Alex Deucher , =?UTF-8?Q?Christian_K=C3=B6nig?= , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , Daniel Stone , Dmitry Baryshkov , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, amd-gfx@lists.freedesktop.org, kernel@collabora.com, Derek Foreman , Marius Vlad References: <20260319-link-bpc-v5-0-5306cd04a708@collabora.com> <6251230.iIbC2pHGDl@workhorse> Content-Language: en-US From: Harry Wentland In-Reply-To: <6251230.iIbC2pHGDl@workhorse> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: YQBPR01CA0160.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:c01:7e::29) To BL1PR12MB5126.namprd12.prod.outlook.com (2603:10b6:208:312::8) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BL1PR12MB5126:EE_|MW4PR12MB6897:EE_ X-MS-Office365-Filtering-Correlation-Id: 04d765b4-4f25-4d02-ac67-08de90da435e X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|7416014|366016|376014|1800799024|18002099003|22082099003|56012099003; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:BL1PR12MB5126.namprd12.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230040)(7416014)(366016)(376014)(1800799024)(18002099003)(22082099003)(56012099003);DIR:OUT;SFP:1101; X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?utf-8?B?K3VjWEZLY2Z0SEpYSkttbE1wYVp0ZHkyZHlaa0FONnZMQUJCMkM4WXd3UFM0?= =?utf-8?B?MGV3WkZFSEF1WTRtR3VDYWhoY2FvKzFCVktLQWVBQUhXRjJEemVDNHR3OThm?= =?utf-8?B?TTZYR0JKVmI2LytkRlhvL29WZEpiMThnQ1E3cEV1djJGZEk3ZGVCZ2J6eEd5?= =?utf-8?B?ck5PcjBwc1A5TW8rZmNwemZVRk4wK2t4SzNuZjd4V29wTVFCdmNFbW1PdGx2?= =?utf-8?B?eEd1ZXpJMmVhRk1XSkxxNTNmaU5tQkFxSkcyNW1rb1hvV1lmc05keWVKekpD?= =?utf-8?B?bXFXSDFnVGQzMXd5OWkxOWhoRE9LZnhYUXFTUWRjK2xrRDhXSHEycHRHNXFk?= =?utf-8?B?RXlNU2VENHpnSEgxanBWQTRoYlduNTFrQ29sTmhEQXJULy9FOVdYSGRsclpF?= =?utf-8?B?aFJYd3Z2ZDVLR3JSa043dkNZaXRBUUJvelE3U2thMnNYSEZ1YnlETHFDTDVo?= =?utf-8?B?S3dJMEQ0NUFqWFRvc0NWeVYrRWltb29qbFByeEFoZU9aYTRvWFdVNk1zUW1j?= =?utf-8?B?M1hveWZobWVoZ3dSLzR3bVBvT3RjbVNscTA0dWFKVFVQTE9DaWoreGJaZWVt?= =?utf-8?B?cW9Jc2txL0dIcEF0MGJKaktlbFNQemgza0VYNzRZdVJHLzlqS0NpSXlnSks3?= =?utf-8?B?U1VoamVXRDQ1MzduZkxwSjN3USticnRVNFllOXlEQUlrdlpjdkoxSW9aV0pN?= =?utf-8?B?NXorOEo3MnptN3d6YSsxMm9nbEdrMFdKSmF2QnJHTnZUNEg2b0VSWG84cWIv?= =?utf-8?B?OTJURWZSV3RaQy9zTEVMZzRXUFN6VGFKNlEvMnYzaktUOWJESEtrTi9oK0dL?= =?utf-8?B?UUdJTks1QTc2SnZGVzVZMlZNMTZnNmJJU05HWHpjbGdGWE1GdVJ6MWRabU93?= =?utf-8?B?SWxPRCtlM3FQZUF4L1Fnb2dxVE1GSUpHMkpzQWhDNWdKTitpMnBmMkhNeUxX?= =?utf-8?B?TllUZXl4VzBjeFJPRWJHNjU0VmxIbmlyaFRqYzhSWGFUa0h3bHBUU1N3dnFL?= =?utf-8?B?S1RBYXBmb2ZpSUNYZHA5c2JlMVhUSjlOTVZCQm5TOUFvVTBVWWVzbGo5U3Zq?= =?utf-8?B?RGJsUHc5QmQ5b2Q0bS9iVlNrL1RMMWZHMk1EUE5YajlGdEgvcXVISEgybnli?= =?utf-8?B?VVhKcnVjR0JtbWlaK2pXeUQ3cVFTRmZ3VFBic1gyNExJYkZpZEdDVlBlcnlP?= =?utf-8?B?ekVIRVVYUDc2N2x2QWxlTnlPaEJoa2ljMWlKTTRKNlRjVDlRbmNzanhkZzQ5?= =?utf-8?B?RVpaNyswc0UxWWhtVnIycjZIa1ZMUzRqTWNSS2FZM2RkSmQ5dTFESEswOFJU?= =?utf-8?B?bE9mK0ZIeWl5MmFzS3BOMFZETHMrMGR2SGJmL3Z3djRJUm5OcjJ0OXpENDRJ?= =?utf-8?B?ai9WWkprbDlvaDA4UERMNWVyQ0ZBbjk2OC9MNWlCa0cvUW9jd0tlc0NlRGRJ?= =?utf-8?B?VTgzUXZ5U283VmlHdXdZVGh3SXlpbHdmY3oxbG5IWlkvc2N3RlJQOGUwSFRk?= =?utf-8?B?N1RncXZxZUFxNnA1Qnl2NGFOT1UwM0hZNHJWOENmOGptc2l0QzhsbmF1Ny9T?= =?utf-8?B?NjhpR1NFbEVzR0xmRDJRWm1jelQxeWt5WGF6MUpqQndBNk01NmpHT3N6OW5F?= =?utf-8?B?bExBd2ExWGxuWmJScCtwL3hxR2pIR0dNVDFKRG4wSmZMdWViM04zSVNOQWVI?= =?utf-8?B?TWZHaVNPRjNvc3VoT0g2ZWx4R0tidTZvWXpZTWhVQlQ4VmhtNW1NWUFNSE5S?= =?utf-8?B?U0NXSlVybDdHVDkzM0cvSk9BT1hLZVBYdjZFWVprUkQ1WDEwZFFLSE9iM2E3?= =?utf-8?B?c0EzbmhIM0ZaRnkvdm5wVk05ellURVArZnRuOHNnaHAxd1MxM2ppSEMxQkE0?= =?utf-8?B?YzJCYlloQXg1Q3VmRzQxM2tGTEx0YlhiNDMvRTFOeERqTlFhenMvbGNIblNG?= =?utf-8?B?TkJzUGtMQnd3RHQ5bUhTUFRUSjRzeFpPUjNsWmdOSXcwNUQzc0ZjOXdLU1Zq?= =?utf-8?B?Qzg0WHJtQUl0cTdXVnUvaE85bFR1VXZzQU5wRGp5eXlpcjZaMzlSbDM2SXBl?= =?utf-8?B?YTF5SXBlVnpadlNzU2FST05uNlRhL0xGcWRkeUNjZFF2akdBRVF6Mlp3WlZQ?= =?utf-8?B?eXczUytNaDdhM0p4OGowUERzZUlBaXZMV09OUGw4TlFZRkR4ZUxkdzZzQnBV?= =?utf-8?B?SHQyNmJxRkNpc1NVOFNPYTBzSkFFMDloSlFLQUFDbHFhZ3d4d21Rei9KUnVV?= =?utf-8?B?aEEvakZtQ3lodGx3M0VxOEtXK3VoamhxTUFrMjV2ejV3aytHTFVmUFcvYm01?= =?utf-8?B?VzFQd3VpaWFxTGpOUGVja04zcFBIZmVwY0pWaXhad2d2WTNkYjl2UT09?= X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-Network-Message-Id: 04d765b4-4f25-4d02-ac67-08de90da435e X-MS-Exchange-CrossTenant-AuthSource: BL1PR12MB5126.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 02 Apr 2026 17:07:04.1569 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 2pVS8fmUxL5E+sYOHqZeXDREz09l/FkCOkL+P1lb9IwAymiF6l72v2jRkcEhffKeEzx2qg7rW6pdrqul/dj67w== X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR12MB6897 On 2026-04-01 08:46, Nicolas Frattaroli wrote: > Chiming in here to basically agree with Daniel and underline his point with > some evidence. > > On Wednesday, 1 April 2026 10:40:15 Central European Summer Time Daniel Stone wrote: >> Hi Harry, >> >> On Tue, 31 Mar 2026 at 18:47, Harry Wentland wrote: >>> On 2026-03-31 08:50, Pekka Paalanen wrote: >>>> People who care about the picture quality down to these levels will >>>> likely want to know and learn about these techniques. They may also >>>> want to explicitly control them. >>>> >>>> In time, when these have been used enough in the wild, compositor >>>> developers will learn what makes a difference and what does not, so >>>> they will adjust their reporting to end users. The most important thing >>>> for the kernel is it offer an unambiguous and stable UAPI for these. >>>> >>>> Policy belongs in userspace. >>> >>> I don't like this as a blanket statement. There is a lot of policy that >>> intersects with HW nuances, whether it comes to power or otherwise. >>> Taking away driver vendor's abilities to optimize will hurt the Linux >>> ecosystem in the long run. >>> >>> IMO this needs to be evaluated on a case by case basis. There are >>> many places where it does make sense to give userspace a greater >>> say on policy, but we don't want to push driver (HW specific) logic >>> up into userspace. >> >> It's not something that's _just_ specific to a particular >> display-controller manufacturer or a particular IP generation though. >> It very much depends on the usecase. >> >> If you have a laptop and you're trying to give a presentation, >> applying dithering and/or DSC makes a lot of sense: you don't want >> your battery to die, and the projector's probably going to obliterate >> half the colour anyway, so might as well as go for the most efficient >> thing. >> >> If your laptop is plugged into your big display at home to write code, >> applying DSC to cram the highest possible resolution + refresh in >> would make sense. But if dithering only results in a marginal power >> saving, and your laptop is charging anyway - why bother degrading >> visual acuity? > > This kind of encourages me to say that the meaning of "bpc" here should > either be reduced by all compression (of which I see dithering as a > primitive variant of) or left at the uncompressed bpc for all compression. > > I'm leaning towards the latter. 10bpc lossily compressed to 8bpc is likely > a better choice than plain 8bpc for visual clarity, so making them look the > same to userspace would result in some odd choices. At the same time, having > a separate way for userspace to know of any compression techniques applied > on the output would disambiguate that for those compositors that really care, > and would also mean we don't have to make subjective judgement calls for > anyone. > > With regards to DSC for example, any vendor's decision to enable it by > default does not necessarily give us a good precedent for what side to > err on. amdgpu flips on DSC when it doesn't have to, and this has rubbed > some people wrong: https://gitlab.freedesktop.org/drm/amd/-/work_items/2043 > I fail to see a convincing explanation on how DSC degrades user experience. No video or anything. It's somewhat difficult to judge the merit of a ticket like that. > The goal isn't so much to push driver logic into userspace, but to give > userspace a view into what the driver did, so that it can decide whether > it's happy or wants to try again differently. This means userspace isn't > ossifying on a set of parameters that made sense a decade ago; drivers can > still modify their decisions as they develop and hardware gains new > techniques. > I agree with this goal. First, reasonable defaults. Secondly, inform userspace, thirdly, let userspace set different configs. In that order. To get #2 and #3 right we need the conversation that Michel started. Harry >> >> If you're a media player, then you're in a good position to know what >> would be good to go over the wire, because you know (& are possibly in >> control of) the format over what comes in in the first place. >> >> But everyone's tradeoffs are different, which is why sometimes the >> best choice is to ultimately leave it up to the user. If you dig into >> any media playback device (STBs running Android TV, Apple TV, Fire TV, >> et al), you'll see that all of them ultimately allow overrides for bpc >> / colour model / subsampling / etc. Those aren't just there for fun, >> but because they are usable to real people, and it's not possible for >> Amlogic or MediaTek or Rockchip or whoever to statically decide that a >> certain configuration is going to be best everywhere. >> >> Right now we have drivers making magic per-vendor/SKU decisions, >> without even so much as a feedback mechanism to userspace (unless you >> count debugfs, maybe) so it can even figure out what's going on, let >> alone control it. To properly support some of those usecases, >> userspace needs to be able to control what goes out on the wire, but >> as a first step, it just wants to be informed of what the driver even >> did with the properties we gave it. >> >> The end game of this isn't Weston logging something to stdout, it's to >> surface things to userspace so it can guide the kernel into making a >> good decision for usecases that may not be ones the silicon vendor >> decided was 'probably the best thing' however many years ago. >> >> Cheers, >> Daniel >> > > Kind regards, > Nicolas Frattaroli > >