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 079F8C433F5 for ; Thu, 24 Mar 2022 14:23:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1350770AbiCXOZK (ORCPT ); Thu, 24 Mar 2022 10:25:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40926 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350769AbiCXOZJ (ORCPT ); Thu, 24 Mar 2022 10:25:09 -0400 Received: from wout5-smtp.messagingengine.com (wout5-smtp.messagingengine.com [64.147.123.21]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 469667938C for ; Thu, 24 Mar 2022 07:23:31 -0700 (PDT) Received: from compute1.internal (compute1.nyi.internal [10.202.2.41]) by mailout.west.internal (Postfix) with ESMTP id 800833200FA9; Thu, 24 Mar 2022 10:23:28 -0400 (EDT) Received: from mailfrontend1 ([10.202.2.162]) by compute1.internal (MEProxy); Thu, 24 Mar 2022 10:23:29 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cerno.tech; h=cc :cc:content-type:date:date:from:from:in-reply-to:in-reply-to :message-id:mime-version:references:reply-to:sender:subject :subject:to:to; s=fm3; bh=BAtPvAjSsi0nB6PDOyaklBbscwTc5uTvowGLL4 pcVqw=; b=BBPaR+Fvvl+JvOzRjkvSf+DONBCzVF15WuJfF3HjSyk90cFy/UXVO2 xTHAP0aYWNGN/ptB/+fEfUG/bPBmDm3b6lDboJMMNHti6xhcKov31o5XcvkRLXxL ev4lMR9KeOGw71UyTHVNKpUpurwKnb5ptBxAmzrGvVImSmQIHyCI0mhFuq7ulcRP ErOpbAhJfLZK1+1R/6wLQNzgBkkcrKDx8Jz+EPWhtTIpT3FTzhiDNoVllzAHv5HH nA4ByWKLGunvJVb6lNIPuhdGERnYRd0w/afJEFPybNZA3gFrU0KodAJKa9gnvTCm zw0STCmKgIzfmB9/wP/lqGm8gXnzs6rw== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:date:date:from:from :in-reply-to:in-reply-to:message-id:mime-version:references :reply-to:sender:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm3; bh=BAtPvAjSsi0nB6PDO yaklBbscwTc5uTvowGLL4pcVqw=; b=NJL83sDtHTj9BSo+P1EjWsc/3b10qaxn4 P0M9dRPc5lT92dJQz0SwROKKIvTBmb8cSV2wB0uxpU0yfUp7pyUszQ5kU8JhVqGE 1xlljLYoIVxx8TR2w3ddZ5FLh5C04VU3jd5NaS2R0pVb4I68wgyRAiGQLU1/51+k mwmwIGt+m3IZxY8Sn1xL5QaGJyq6kJrC4pnYBJrvBM0vI4Nqea7yTihIFrjXSfRV /FhHjADI+0aPVJTgJ2P14z0xrxGA03NgtHsQw83OIy9ii5MxTgmAP3xSgLH09rh5 I4cPGhY51igCSqMhBYBPoBEbL8blrk4DVwIlwNI04EPmCF3GGrXSw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvvddrudegledgheelucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepfffhvffukfhfgggtuggjsehgtderredttddvnecuhfhrohhmpeforgigihhm vgcutfhiphgrrhguuceomhgrgihimhgvsegtvghrnhhordhtvggthheqnecuggftrfgrth htvghrnhepleekgeehhfdutdeljefgleejffehfffgieejhffgueefhfdtveetgeehieeh gedunecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepmh grgihimhgvsegtvghrnhhordhtvggthh X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 24 Mar 2022 10:23:26 -0400 (EDT) Date: Thu, 24 Mar 2022 15:23:24 +0100 From: Maxime Ripard To: Laurent Pinchart Cc: Rob Herring , Frank Rowand , devicetree@vger.kernel.org, dri-devel@lists.freedesktop.org, Andrzej Hajda , Neil Armstrong , Robert Foss , Jonas Karlman , Jernej Skrabec , Daniel Vetter , David Airlie , Jagan Teki , Marek Vasut , Sakari Ailus Subject: Re: [PATCH] dt-bindings: display: bridge: Drop requirement on input port for DSI devices Message-ID: <20220324142324.monalktzzpypu74x@houat> References: <20220323154823.839469-1-maxime@cerno.tech> <20220324081819.niz4pdqu3j7n2ivh@houat> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="kq735fu2dw67hzsc" Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org --kq735fu2dw67hzsc Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Mar 24, 2022 at 03:43:42PM +0200, Laurent Pinchart wrote: > On Thu, Mar 24, 2022 at 09:18:19AM +0100, Maxime Ripard wrote: > > On Wed, Mar 23, 2022 at 10:38:19PM +0200, Laurent Pinchart wrote: > > > Hi Maxime, > > >=20 > > > (CC'ing Sakari) > > >=20 > > > Thank you for the patch. > > >=20 > > > On Wed, Mar 23, 2022 at 04:48:23PM +0100, Maxime Ripard wrote: > > > > MIPI-DSI devices, if they are controlled through the bus itself, ha= ve to > > > > be described as a child node of the controller they are attached to. > > > >=20 > > > > Thus, there's no requirement on the controller having an OF-Graph o= utput > > > > port to model the data stream: it's assumed that it would go from t= he > > > > parent to the child. > > > >=20 > > > > However, some bridges controlled through the DSI bus still require = an > > > > input OF-Graph port, thus requiring a controller with an OF-Graph o= utput > > > > port. This prevents those bridges from being used with the controll= ers > > > > that do not have one without any particular reason to. > > > >=20 > > > > Let's drop that requirement. > > >=20 > > > I'm sure this won't come as a surprise, I'm very much opposed to this > > > change, for two reasons. > > >=20 > > > First, ports are part of the hardware, even if they're not connected.= It > > > thus simplifies handling in drivers if they're always present. > > >=20 > > > Then, and that's the most important reason, I think it's a mistake not > > > to model the DSI data connection using OF graph unconditionally, even > > > when the DSI sink device is also controlled through the DSI bus (using > > > DCS) and is in that case a child of the DSI source device in the DT > > > hierarchy. > >=20 > > That's the way we do for any other device though. You never addressed > > that comment, but it's very much the same that occurs for i2c or spi > > controllers and their device. They all get their data from the parent > > bus. I don't see you advocate for using OF-Graph for those devices. >=20 > Those are different, there's no data stream independent of the control > communications. Fine, then you have Ethernet PHYs, or any MMIO device that does DMA. > > > The device tree describes a control hierarchy between devices. OF gra= ph > > > overlays on top of that a data transfer graph. The two are different > > > concepts, and the fact that DSI can sometimes be used as a control bus > > > doesn't change the concept. Using OF graph unconditionally to describe > > > the data connections for DSI leads to less variation in the device tr= ee > > > structure, and thus less complexity in the implementation. We're > > > suffering from the fact we haven't made it a requirement in the first > > > place, which can't be fixed due to ABI breakage constraints, but let's > > > not acknowledge it as a good idea. > >=20 > > Honestly, it doesn't matter one bit. > >=20 > > We have a huge discrepancy here today, and only a couple of bridges have > > that arbitrary restriction. The situation you don't want to acknowledge > > is the de-facto standard, by the generic binding and by what all the > > bridges and panels are implementing. Even panel-simple-dsi is doing it. > > So it's very much there already. >=20 > It's here, and I think we should move away from it for new DSI sinks. > I'd like OF graph to be used consistently for new drivers. We can't > change existing DT bindings and drivers to drop support for the > non-OF-graph description due to ABI stability, but we can avoid > repeating the mistake going forward. > > > What I'm trying to address here is that some controllers that do > > everything right can't be used because that restriction is completely > > arbitrary and in opposition to the consensus. And they can't be used > > *today*. > >=20 > > If we want to change that consensus, fine, but we should still have one. > > Having some bridges enforcing custom rules for no reason is very much > > unacceptable. > >=20 > > And changing that consensus won't happen overtime, we'll have to take > > care of the backward compatibility, etc. So it won't fix the issue that > > we can't use any bridge with any controller any time soon. >=20 > I don't think that's the issue at hand here. You can still use a > non-OF-graph DT event if the nodes for the two bridges affected by this > patch define a port@0. It can just be left unconnected. >=20 > I do agree it will cause some DT bindings for DCS-based DSI sinks to > have ports will others won't. If your concern is that all DT bindings > should be coherent, would you be OK with a patch that makes the sink > port mandatory in all DT bindings for DSI bridges and panels (and fixes > the mainline DT sources accordingly to make sure they validate) ? The > port would not be connected of course (at least when used with DSI > source drivers that don't use OF graph today). That would make DT > bindings coherent, and would be a first step towards using OF graph > everywhere. I'm trying to fix a (recent) mistake/cargo-cult in new bindings. That discussion is not going to be fairly controversial and I don't see how that can be solved quickly. So, as a second step, why not. But this one needs to come first. Maxime --kq735fu2dw67hzsc Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYKAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCYjx+3AAKCRDj7w1vZxhR xRLoAQCTIpIMWpib5N/OdprcjAAx1ppjIy53NN2C7tfT3MMDHgEA2nt3GKD2CVrB mj/pjIsjnm83gSZpQyfBwM99I9RCJAM= =SFux -----END PGP SIGNATURE----- --kq735fu2dw67hzsc--