From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-pp-f112.zoho.com (sender4-pp-f112.zoho.com [136.143.188.112]) (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 076F536494A for ; Wed, 1 Apr 2026 12:15:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.112 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775045728; cv=pass; b=KOivhbRPL6VGEqEsDgxkzKkJtduBXPqLENHfn1OQNUdZxqsaIxArkLjvWBt0GL+qZIy98QZVPtaOXWUTHZoMrTeYVrPCR3XYzIQMCWOqQSBaDjRUSya58w7UzYU1WNpaLHxEZnbcy7A4DCocO+E2XxBKTFwhkTOWl0RhMQ2yk7E= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1775045728; c=relaxed/simple; bh=Q5UP4+Y2rITW+tf6Rd44ZPztWp3eUT3BShmZpWQKL5I=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=FLp+VjgPZ+8ROzrSL083w/AVRYITZ3tz8UMBlgIXUHrZZp+PaDOcNPF61FGAciYe1AU7FLXbIjXVglZP6RdnLRtEJscSzGO+cP9ZjFhjyWVINiD4oygJBtRCAhgD7PM0VyVBAUfwbZsIdlSIGZ1cyGZ0GqMGVDLZvmzyiMh3+fc= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (1024-bit key) header.d=collabora.com header.i=nicolas.frattaroli@collabora.com header.b=DmCgzbl8; arc=pass smtp.client-ip=136.143.188.112 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=collabora.com header.i=nicolas.frattaroli@collabora.com header.b="DmCgzbl8" ARC-Seal: i=1; a=rsa-sha256; t=1775045689; cv=none; d=zohomail.com; s=zohoarc; b=KaAXEGGMiKIIaIoGgo79W+We9AmkrITz7h8K2gQHnYE5PSRD8SkbD32hovXZqEosucv41LEvyuFdWIONCB8GuFNqs8N/eU8wUYQ1Vf0GbM2cEolVUfe4LHhYVcS5oywOPey+PURdt1c/W/lJOO6ef9aGvmeKU91j4E3GOTuonX0= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1775045689; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=XiDS3s5yYlqvswVEQyjuSwI4C0tCZYmt0PdRdLxftNM=; b=nPFKV49BNf5LI78APcB/aVM/iKiUbTWTrwOIfbJfmZhLUgvC5l4wPSgQ8Rt8VUlcl7TuDeYsHT4kKOj8KfgILYPfwz3Nhm3IpUVLqQALIjDCUIn2X20uH7ZWEA4sGNozGImXIjI+rBK+lNS/8Xnbp/wHLFFpnnarkqyiwSS6qcE= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=nicolas.frattaroli@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1775045689; s=zohomail; d=collabora.com; i=nicolas.frattaroli@collabora.com; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-ID:In-Reply-To:References:MIME-Version:Content-Transfer-Encoding:Content-Type:Message-Id:Reply-To; bh=XiDS3s5yYlqvswVEQyjuSwI4C0tCZYmt0PdRdLxftNM=; b=DmCgzbl85uJWWVum+9TY6Tiv0DFvjwetvPyuGR2b8cs+2nIGw/Oc6KgF+TFd7dyY h8iPOp1UOFjl0BpG/ytlRy55cZHYDXns+qa5NL3uAMOX33AOe1XtqgjI+qCiVmaACmV jF4DTekNocBKVbFcHLsdCYEJh5Nx7yEzxuTSQJyU= Received: by mx.zohomail.com with SMTPS id 1775045687069364.77452819437485; Wed, 1 Apr 2026 05:14:47 -0700 (PDT) From: Nicolas Frattaroli To: Xaver Hugl Cc: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Harry Wentland , Leo Li , Rodrigo Siqueira , Alex Deucher , Christian =?UTF-8?B?S8O2bmln?= , Ville =?UTF-8?B?U3lyasOkbMOk?= , 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 , wayland-devel@lists.freedesktop.org Subject: Re: [PATCH v5 0/3] Add "link bpc" DRM property Date: Wed, 01 Apr 2026 14:14:40 +0200 Message-ID: <4970515.ElGaqSPkdT@workhorse> In-Reply-To: References: <20260319-link-bpc-v5-0-5306cd04a708@collabora.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" On Wednesday, 1 April 2026 13:57:08 Central European Summer Time Xaver Hugl= wrote: > Am Do., 19. M=C3=A4rz 2026 um 13:28 Uhr schrieb Nicolas Frattaroli > : > > > > This series adds a new "link bpc" DRM property. It reflects the display > > link's actual achieved output bits per component, considering any > > degradation of the bit depth done by drivers for bandwidth or other > > reasons. The property's value is updated during an atomic commit, which > > is also when it fires an uevent if it changed to let userspace know. >=20 > Hi, > I think it's a really good idea to have a property for knowing the > actual bpc of the link... however, I do have one big concern with this > API specifically: It only gives me this information after a modeset. >=20 > With this limitation, I can at most show the user which bpc was chosen > after the apply display settings and have the end user manually test > and figure things out, but I cannot show in the UI which bpc will be > chosen with some configuration before they apply it, and I cannot do > atomic tests to find a desired tradeoff automatically on the > compositor side. To do this I'd need to see if there's some feedback mechanism for the output configuration chosen by the atomic check phase, so that userspace can then run a DRM_MODE_ATOMIC_TEST_ONLY and get the value back somehow. The current implementation wouldn't be able to do this since it updates the property on commit_tail. I'll need to look into whether drivers already have everything figured out with regards to link bpc in the check phase, and how that would best be communicated to userspace. > As a side note, for future patches relevant for compositors, please cc > wayland-devel. It really shouldn't be up to chance whether or not > compositor developers that would later use the API find out about it > before it's merged, and keeping track of all of dri-devel is way too > much to ask from userspace developers. I'll do that, but consider using lei[1] to have saved searches on lore delivered to a local Mailbox, a suitable query here may be dfb:drm_property which will return all e-mails with diffs matching added lines with "drm_property" in them, from which lei can then fetch the full threads. >=20 > - Xaver >=20 Kind regards, Nicolas Frattaroli https://people.kernel.org/monsieuricon/lore-lei-part-1-getting-started [1]