From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2F89EC433EF for ; Wed, 6 Apr 2022 11:42:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229562AbiDFLow (ORCPT ); Wed, 6 Apr 2022 07:44:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:44016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230269AbiDFLoV (ORCPT ); Wed, 6 Apr 2022 07:44:21 -0400 Received: from relay6-d.mail.gandi.net (relay6-d.mail.gandi.net [217.70.183.198]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5ED6A19C2A for ; Wed, 6 Apr 2022 01:30:41 -0700 (PDT) Received: (Authenticated sender: paul.kocialkowski@bootlin.com) by mail.gandi.net (Postfix) with ESMTPSA id CAABEC0004; Wed, 6 Apr 2022 08:30:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1649233839; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=x58PUGpYCESbbCtEZlbi5sZBeRskMKKvlojIazBIayg=; b=d0wVV32QEFvychcF08K0IwDp8FoTXZ2CJnGZWtqGuf79n2hPuOqEMgLNj4aAayLv5sTLZv REkIZxkFKkU+37sIkxn1dgsW6cVmDp+B3xJ8vTB/Si5og7LVUtgTfK+q7KCmtQKWFffD9K +TXBlJzZ9/yKj5lFvVdtyOBUo0ExX5vcdAIJ+pq/KWfO+B+Cy1I451QiaJsXgYje0Pmomw rVBEwJMaPk0vahFkp9jRsAB91V+pLbPg3bayx1qDSfzpezY/5kNrhzcF0NbfUMiBeYTFks 5OcB6k9vUFy600orslqrcyFSrA9AXORsvG5VYMorAACPKS1PXsL7JSbSlRnSQA== Date: Wed, 6 Apr 2022 10:30:38 +0200 From: Paul Kocialkowski To: Thierry Reding Cc: Bjorn Andersson , Thomas Petazzoni , David Airlie , linux-kernel@vger.kernel.org, Kuogee Hsieh , dri-devel@lists.freedesktop.org, Thomas Zimmermann , Dmitry Baryshkov , Jagan Teki Subject: Re: [PATCH v3] drm: of: Properly try all possible cases for bridge/panel detection Message-ID: References: <20220329132732.628474-1-paul.kocialkowski@bootlin.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="0yOxSLaMWlYo0LFA" Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --0yOxSLaMWlYo0LFA Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Hi Thierry, On Tue 05 Apr 22, 19:00, Thierry Reding wrote: > On Fri, Apr 01, 2022 at 09:44:46AM +0200, Paul Kocialkowski wrote: > > Hi Bjorn, > >=20 > > On Thu 31 Mar 22, 20:16, Bjorn Andersson wrote: > > > On Tue 29 Mar 06:27 PDT 2022, Paul Kocialkowski wrote: > > >=20 > > > > While bridge/panel detection was initially relying on the usual > > > > port/ports-based of graph detection, it was recently changed to > > > > perform the lookup on any child node that is not port/ports > > > > instead when such a node is available, with no fallback on the > > > > usual way. > > > >=20 > > > > This results in breaking detection when a child node is present > > > > but does not contain any panel or bridge node, even when the > > > > usual port/ports-based of graph is there. > > > >=20 > > > > In order to support both situations properly, this commit reworks > > > > the logic to try both options and not just one of the two: it will > > > > only return -EPROBE_DEFER when both have failed. > > > >=20 > > >=20 > > > Thanks for your patch Paul, it fixed a regression on a device where I > > > have a eDP bridge with an of_graph and a aux-bus defined. > > >=20 > > > But unfortunately it does not resolve the regression I have for the > > > USB based DisplayPort setup described below. > > >=20 > > >=20 > > > In the Qualcomm DisplayPort driver We're calling: > > >=20 > > > devm_drm_of_get_bridge(dev, dev->of_node, 1, 0); > > >=20 > > > and with the following DT snippet the behavior changed: > > >=20 > > > displayport-controller@ae90000 { > > > compatible =3D "qcom,sc8180x-dp"; > > > ... > > >=20 > > > operating-points-v2 =3D <&dp0_opp_table>; > > >=20 > > > ports { > > > #address-cells =3D <1>; > > > #size-cells =3D <0>; > > >=20 > > > port@0 { > > > reg =3D <0>; > > > dp0_in: endpoint { > > > remote-endpoint =3D <&display_driver>; > > > }; > > > }; > > > }; > > >=20 > > > dp0_opp_table: opp-table { > > > ...; > > > }; > > > }; > > >=20 > > > Prior to the introduction of 80253168dbfd ("drm: of: Lookup if child > > > node has panel or bridge") this would return -ENODEV, so we could > > > differentiate the case when we have a statically defined eDP panel fr= om > > > that of a dynamically attached (over USB) DP panel. > > >=20 > > > Prior to your change, above case without the opp-table node would have > > > still returned -ENODEV. > > >=20 > > > But now this will just return -EPROBE_DEFER in both cases. > >=20 > > Oh that's right, the -ENODEV case was just completely removed by my cha= nge. > > Initially this would happen if !of_graph_is_present or if the remote no= de > > doesn't exist. > >=20 > > Now that we are also checking for child nodes, we can't just return -EN= ODEV > > when the graph or remote node is missing: we must also check that there= is no > > child node that is a panel/bridge. > >=20 > > For the graph remote case, we can reliabily return -EPROBE_DEFER when > > of_graph_is_present and the remote exists and of_device_is_available. > > Otherwise we can go for -ENODEV. I think getting -EPROBE_DEFER at this = point > > should stop the drm_of_find_panel_or_bridge process. > >=20 > > On the other hand for the child panel/bridge node case, I don't see how= we > > can reliably distinguish between -EPROBE_DEFER and -ENODEV, because > > of_drm_find_panel and of_drm_find_bridge will behave the same if the ch= ild > > node is a not-yet-probed panel/bridge or a totally unrelated node. > > So I think we should always return -EPROBE_DEFER in that case. > >=20 > > As a result you can't get -ENODEV if using the of graph while having any > > (unrelated) child node there, so your issue remains. > >=20 > > Do you see any way we could make this work? > >=20 > > > I thought the appropriate method of referencing the dsi panel was to > > > actually reference that using the of_graph, even though it's a child = of > > > the dsi controller - that's at least how we've done it in e.g. [1]. > > > I find this to be much nicer than to just blindly define that all > > > children of any sort of display controller must be a bridge or a pane= l. > >=20 > > Yes I totally agree. Given that using the child node directly apparently > > can't allow us to distinguish between -EPROBE_DEFER/-ENODEV I would be = in > > favor of dropping this mechanism and going with explicit of graph in an= y case > > (even if it's a child node). I don't see any downside to this approach. > >=20 > > What do yout think? >=20 > This patch has recently starting causing failures on various Tegra > devices that use drm_of_find_panel_or_bridge() for the case where the > output might be connected to an eDP or LVDS panel. However, that same > output could also be connected to an HDMI or DP monitor, in which case > we obviously don't want a DT representation because it's all > discoverable. >=20 > If I understand correctly, that's similar to what Bjorn described. In my > case I was able to fix the regression by returning -ENODEV at the very > end of the function (i.e. no matching ports were found and no graph is > present). Okay so I'll send a patch that returns -ENODEV when possible, but there is still a case where we can't distinguish between -EPROBE_DEFER and -ENODE= V, which calls for removing the whole child node-based mechanism. Paul --=20 Paul Kocialkowski, Bootlin Embedded Linux and kernel engineering https://bootlin.com --0yOxSLaMWlYo0LFA Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEJZpWjZeIetVBefti3cLmz3+fv9EFAmJNT64ACgkQ3cLmz3+f v9GHXAf+I7lNzoF+dBJbZYSkY3LfZOYIFKgzdHp6vgNm0qCjCqH3OeQoLqIpSA9D hc4ePKaNeO1hCWbdAIqUnlbcrVRX8WDxZnzsKT9mDltsr928el9BeSMybUiIzRzz 1n/Oaxm2sz+5q8Pd9Zo98eZKArECSqPN89oBCq2ur0xPDsVVrwnlDG6GGu01O7HT m+4TqKE+zI50cFQ0bf8vOIIDS9A4XVQhJ91fMr4Qt8uoImiiTMbudooG55WTNyaM R4/1NPFvB+awBLh44lXq69dcWR91HB5v0qExhXFQuuvrE1+5x/d0rg4sCpNrTq3k Wu2OJ+0FIrQehcMtxias/2CVFmWwQw== =j6eO -----END PGP SIGNATURE----- --0yOxSLaMWlYo0LFA--