From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout-04.galae.net (smtpout-04.galae.net [185.171.202.116]) (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 D59533AC0E7 for ; Mon, 13 Apr 2026 12:10:18 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.171.202.116 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776082222; cv=none; b=s5ywqT349VwnDeJ+0LnLjqOIHI++32ixU9Ic9RaXKqO9lgNPNtzFYNzyria1wupFI1Qb4miBFCfhfOAj5ger7xtOL4wkajeKGv1jhheGymxIYx0FleE/NV+4ZDiVhqBjPBk5P6reX1XEBpO9aKaYnbDmfPJGm9duBg02lGFNBdc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776082222; c=relaxed/simple; bh=aLnygnnnYw1YhNxwASb6nv2mPjKSZNKf9PjWtGcflAk=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=fHDTBMzMYPCsM5T1R4of65NuJEEDBPXrH9o7Noz/Sx9TatBnweKHlkgzwC+CMARbytnfOECGLs3rP497QPgd0ee3JYLfU4CmyT8nYR+vWm7vYRGaNdbaW4sWTx3+ubOWtRY9LcGrnegTsuUMVB/+ccN+6ZUGC5OEjTa0hfXSoFw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=XgDbUsd0; arc=none smtp.client-ip=185.171.202.116 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="XgDbUsd0" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-04.galae.net (Postfix) with ESMTPS id 9C3ADC5C183; Mon, 13 Apr 2026 12:10:53 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id EEFD25FFB9; Mon, 13 Apr 2026 12:10:16 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id AA50A104500A2; Mon, 13 Apr 2026 14:10:02 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1776082215; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=dhpDLI3GbjEnq5ea2C3CSlaeOYOoDERSaq/PhF217/g=; b=XgDbUsd0kza50SBVz4+wc3tba3Gea/Rw9Wtl9Oh3cj1zYYyx83GshUatFgLe99itaxWAJf dbLqFjb/kWwi0Lrqgc0awLQeFS+zivNYqgAQVEqYi8w3nolcV+k65uHo3kdCaoU8FmQRYi FNnxTfJNQn5FvhrAeOubTD8A5Hs74ZXx+AAtTu4zM20gVeAwAclh1G1dVmBb9dY1Eir7Jq fvH5aaDiIW27DKzBoQbqfzu2fOc/1o1RsElFMmpjnd6CCy0Z1XUpibM/HsTJ3u3RLvDctq J8mv0Uvt+qvEaqgfRTVFVct2t/QHp9kY5w5CLgxJtUaDj7TEc6nIau/Ea77HiQ== Date: Mon, 13 Apr 2026 14:10:00 +0200 From: Kory Maincent To: Dmitry Baryshkov Cc: Ville =?UTF-8?B?U3lyasOkbMOk?= , Jani Nikula , Rodrigo Vivi , Joonas Lahtinen , Tvrtko Ursulin , David Airlie , Simona Vetter , Dave Airlie , Jesse Barnes , Eric Anholt , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Chun-Kuang Hu , Philipp Zabel , Matthias Brugger , AngeloGioacchino Del Regno , Chris Wilson , Thomas Petazzoni , Mark Yacoub , Sean Paul , Louis Chauvet , intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, linux-arm-kernel@lists.infradead.org, Simona Vetter Subject: Re: [PATCH RFC 00/12] Add support for DisplayPort link training information report Message-ID: <20260413141000.0e190dcc@kmaincent-XPS-13-7390> In-Reply-To: References: <20260409-feat_link_cap-v1-0-7069e8199ce2@bootlin.com> Organization: bootlin X-Mailer: Claws Mail 4.2.0 (GTK 3.24.41; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Last-TLS-Session-Version: TLSv1.3 On Fri, 10 Apr 2026 00:36:09 +0300 Dmitry Baryshkov wrote: > On Thu, Apr 09, 2026 at 11:36:21PM +0300, Ville Syrj=C3=A4l=C3=A4 wrote: > > On Thu, Apr 09, 2026 at 07:08:16PM +0200, Kory Maincent wrote: =20 > > > DisplayPort link training negotiates the physical-layer parameters ne= eded > > > for a reliable connection: lane count, link rate, voltage swing, > > > pre-emphasis, and optionally Display Stream Compression (DSC). Curren= tly, > > > each driver exposes this state in its own way, often through > > > driver-specific debugfs entries, with no standard interface for users= pace > > > diagnostic and monitoring tools. > > >=20 > > > This series introduces a generic, DRM-managed framework for exposing = DP > > > link training state as standard connector properties, modeled after t= he > > > existing HDMI helper drmm_connector_hdmi_init(). > > >=20 > > > The new drmm_connector_dp_init() helper initializes a DP connector and > > > registers the following connector properties to expose the negotiated= link > > > state to userspace: > > >=20 > > > - num_lanes: negotiated lane count (1, 2 or 4) > > > - link_rate: negotiated link rate > > > - dsc_en: whether Display Stream Compression is active > > > - voltage_swingN: per-lane voltage swing level (lanes 0-3) > > > - pre_emphasisN: per-lane pre-emphasis level (lanes 0-3) =20 > >=20 > > I don't see why any real userspace would be interested in those (apart > > from maybe DSC). If this is just for diagnostics and whatnot then I > > think sysfs/debugfs could be a better fit. =20 >=20 > I'd agree here. Please consider implementing it as a debugfs interface, > possibly reusing the Intel's format. Sorry, I completely forgot to include a paragraph explaining the rationale behind using DRM properties. This DisplayPort link information report was requested by OSes to allow the= m to assess the capabilities of each DisplayPort connector on the system, and to guide users from the most to least capable ones. It will also enable the OS= to warn the user when a cable is too long or experiencing noise (indicated by = high voltage swing and pre-emphasis levels). Since this is information that OSes will consume on a regular basis, exposi= ng it directly as DRM properties seems the most appropriate approach.=20 Regards, --=20 K=C3=B6ry Maincent, Bootlin Embedded Linux and kernel engineering https://bootlin.com