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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B383AE7718B for ; Wed, 1 Jan 2025 22:38:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=pWtGsC6VD7JbMPGWl8EVOk9EyjRNOLRXagxmqa1Awn4=; b=slTpbTEweOtRCXedAcanYRZYYu bDKNxPqF96D4/NOVA9t6f/BCyPWZwQph4kehllz24z33qPy/2mzHmBBYIwfKJY8vIFgGjjuJf2ONn mgQwnnULrjodVvtjJ6WrZI0HmTfFaphtuKAd9a5NEyJEYNxGbhiQBCkpAGwgH95p7gG4WRhjNGwux +4brJIGh2qTptn+A+AnfL5ZLh438ymEcr9+Z8VOqHNs4JQJ4yDxpTHuRfvwArWyRSsog/FApyVrGv vy0zY6f2I6HCsHkXT6ma6XGwMZgI6KQgnY6ln9WUIsUD7gc5QMZU5Gd/fh4ov3keKJGOeMYfS5dPB R1jS7NnQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98 #2 (Red Hat Linux)) id 1tT7LQ-00000009RA6-0ejQ; Wed, 01 Jan 2025 22:37:40 +0000 Received: from perceval.ideasonboard.com ([213.167.242.64]) by bombadil.infradead.org with esmtps (Exim 4.98 #2 (Red Hat Linux)) id 1tT7KC-00000009R4M-0KQp for linux-arm-kernel@lists.infradead.org; Wed, 01 Jan 2025 22:36:25 +0000 Received: from pendragon.ideasonboard.com (81-175-209-231.bb.dnainternet.fi [81.175.209.231]) by perceval.ideasonboard.com (Postfix) with ESMTPSA id BC886778; Wed, 1 Jan 2025 23:35:31 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=ideasonboard.com; s=mail; t=1735770931; bh=iNsUYUiEGnb6iomJgG7ri6tQFUsvekg+LieM8mXv0LI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=HN25fJ9Uo0EujdCHA2A8+alerR+ls8x0zaHaJVziAbh8RG+Rt/T84/+weZt7P/Jch ci58r2q2MApprmFn93DRlQVXV9bmfhe5Kri4mklEOTuvRBPB5XX+ULQHbbST48fZAG wZUN+NucQCH+YLdg4jz/+Y5SMxmOTFDmHV0z+ff8= Date: Thu, 2 Jan 2025 00:36:20 +0200 From: Laurent Pinchart To: Marek Vasut Cc: dri-devel@lists.freedesktop.org, Andrzej Hajda , David Airlie , Fabio Estevam , Jernej Skrabec , Jonas Karlman , Liu Ying , Maarten Lankhorst , Maxime Ripard , Neil Armstrong , Pengutronix Kernel Team , Robert Foss , Sascha Hauer , Shawn Guo , Simona Vetter , Stefan Agner , Thomas Zimmermann , imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v3 1/4] drm: bridge: dw_hdmi: Add flag to indicate output port is optional Message-ID: <20250101223620.GA7206@pendragon.ideasonboard.com> References: <20241231192925.97614-1-marex@denx.de> <20241231203136.GD31768@pendragon.ideasonboard.com> <88778e2b-8c43-46a1-bb79-0d9c968a5233@denx.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <88778e2b-8c43-46a1-bb79-0d9c968a5233@denx.de> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250101_143624_255124_E2BC0253 X-CRM114-Status: GOOD ( 27.81 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Dec 31, 2024 at 10:10:51PM +0100, Marek Vasut wrote: > On 12/31/24 9:31 PM, Laurent Pinchart wrote: > > Hi Marek, > > Hi, > > > Thank you for the patch. > > > > On Tue, Dec 31, 2024 at 08:28:48PM +0100, Marek Vasut wrote: > >> Add a flag meant purely to work around broken i.MX8MP DTs which enable > >> HDMI but do not contain the HDMI connector node. This flag allows such > >> DTs to work by creating the connector in the HDMI bridge driver. Do not > >> use this flag, do not proliferate this flag, please fix your DTs. > > > > What's the rationale for this, what prevents fixing DT instead of using > > this flag ? Adding such a flag will most likely open the door to > > proliferation. > > See the V2 series discussion, there are a few in-tree DTs which do not > have the HDMI connector node. The rationale is there might be more and > they might come from vendors, so this flag is necessary to work around > those DTs. > > > If you can't fix the DT on particular boards, patching it could be an > > option. We had a similar problem on Renesas boards, which we fixed with > > a DT overlay, see commit 81c0e3dd82927064 ("drm: rcar-du: Fix legacy DT > > to create LVDS encoder nodes"). This made the workaround self-contained, > > and allowed dropping it several kernel versions later (in commit > > 841281fe52a769fe, "drm: rcar-du: Drop LVDS device tree backward > > compatibility"). > > Frankly, I would much rather fix the few in-tree DTs and mandate the > HDMI connector node in DT, which would keep the code simple, rather than > maintain a backward compatibility workaround for problem which might not > even exist. The in-tree device tree sources should be converted as part of the series, I don't see a point trying to maintain backward compatibility for in-tree DT sources. For out-of-tree sources it depends on how likely the problem is. There's no regression if nobody is affected. I personally like restricting backward compatibility to the strict minimum, to ensure that all new DTs will use proper bindings. Making the backward compatibility code self-contained helps there, and we could also print a loud warning (WARN_ON() seems appropriate) and set a date for the removal of the workaround. -- Regards, Laurent Pinchart