Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755884AbbHYOSP (ORCPT ); Tue, 25 Aug 2015 10:18:15 -0400 Received: from hqemgate15.nvidia.com ([216.228.121.64]:3975 "EHLO hqemgate15.nvidia.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755682AbbHYOSL (ORCPT ); Tue, 25 Aug 2015 10:18:11 -0400 X-PGP-Universal: processed; by hqnvupgp08.nvidia.com on Tue, 25 Aug 2015 07:18:11 -0700 Date: Tue, 25 Aug 2015 16:16:43 +0200 From: Thierry Reding To: Yakir Yang CC: Rob Herring , Heiko Stuebner , Jingoo Han , Fabio Estevam , Inki Dae , Joe Perches , Russell King , Sean Paul , Takashi Iwai , dri-devel , Andrzej Hajda , Gustavo Padovan , "linux-samsung-soc@vger.kernel.org" , Vincent Palatin , , Kishon Vijay Abraham I , David Airlie , "devicetree@vger.kernel.org" , Pawel Moll , Ian Campbell , Doug Anderson , "Rob Herring" , "linux-arm-kernel@lists.infradead.org" , Mark Yao , "linux-kernel@vger.kernel.org" , Kyungmin Park , Daniel Kurtz , Philipp Zabel , Kumar Gala , Ajay kumar , Andy Yan Subject: Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for analogix_dp Message-ID: <20150825141642.GA3820@ulmo.nvidia.com> References: <1439995728-18046-1-git-send-email-ykk@rock-chips.com> <1439995834-18363-1-git-send-email-ykk@rock-chips.com> <20150825091534.GB14034@ulmo.nvidia.com> <55DC7211.9080601@rock-chips.com> MIME-Version: 1.0 In-Reply-To: <55DC7211.9080601@rock-chips.com> X-NVConfidentiality: public User-Agent: Mutt/1.5.23+89 (0255b37be491) (2014-03-12) X-Originating-IP: [10.2.70.11] X-ClientProxiedBy: UKMAIL102.nvidia.com (10.26.138.15) To drukmail101.nvidia.com (10.25.59.19) Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="7JfCtLOvnd9MIVvH" Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3750 Lines: 94 --7JfCtLOvnd9MIVvH Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Tue, Aug 25, 2015 at 09:48:01PM +0800, Yakir Yang wrote: > Hi Thierry & Rob, >=20 > =E5=9C=A8 2015/8/25 21:27, Rob Herring =E5=86=99=E9=81=93: > >On Tue, Aug 25, 2015 at 4:15 AM, Thierry Reding wro= te: > >>On Sun, Aug 23, 2015 at 06:23:14PM -0500, Rob Herring wrote: > >>>On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang wrote: > >>[...] > >>>>+ -analogix,link-rate: > >>>>+ max link rate supported by the eDP controller. > >>>>+ LINK_RATE_1_62GBPS =3D 0x6, LINK_RATE_2_70GBP= S =3D 0x0A, > >>>>+ LINK_RATE_5_40GBPS =3D 0x14 > >>>Same here. I'd rather see something like "link-rate-mbps" and use the > >>>actual rate. > >>There is no need whatsoever to hard-code this in DT. (e)DP provides the > >>means to detect what rate the link supports and the specification > >>provides guidance on how to select an appropriate one. > >Good, even better. >=20 > I do think we still need keep this DT prop yet. >=20 > I think drm_dp_help.c could get the "panel" max link-rate and lane-count, > but it's not enough, we still need knew the "eDP controller" max link-rate > and lane-count. >=20 > Let me show the exact example that happened in my side. When I connect > my board to my 2K DP-1.2 TV. Analogix dp driver would get the max link-ra= te > from dpcd, and the max link-rate is 5.4Gbps. So if I just set eDP control= ler > link-rate > to 5.4Gbps, the DP TV just broken, do not light up normally. >=20 > This reason why TV broken is the max link-rate which support by RK3288 eDP > controller is 2.7Gbps. Here are the exact words that RK3288 eDP TRM said: >=20 > *=EF=81=AC=EF=80=A0Compliant with DisplayPortTM Specification, Version 1.= 2. > =EF=81=AC=EF=80=A0Compliant with eDPTM Specification, Version 1.3. > =EF=81=AC=EF=80=A0HDCP v1.3 amendment for DisplayPortTM Revision 1.0. > =EF=81=AC=EF=80=A0Main link containing 4 physical lanes of 2.7/1.62 Gbps/= lane > * > ** >=20 >=20 > Beside I haven't found there are some registers would indicate the eDP > controller > max link-rate and lane-count, so this is why I still instance that we need > this DT > prop to indicata "Max rate controller support". >=20 > So, I wish you could agree with me on this point. Your driver should know what link rates it supports and restrict itself to use those. This is implied by the compatible string and doesn't need to be duplicated into device tree. 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