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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 0A876C61DD3 for ; Tue, 1 Sep 2026 14:31:00 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 3D14810ED19; Tue, 1 Sep 2026 14:30:59 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=bootlin.com header.i=@bootlin.com header.b="NLej3Sc/"; dkim-atps=neutral Received: from smtpout-03.galae.net (smtpout-03.galae.net [185.246.85.4]) by gabe.freedesktop.org (Postfix) with ESMTPS id BAD2710ED19 for ; Tue, 1 Sep 2026 14:30:57 +0000 (UTC) Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-03.galae.net (Postfix) with ESMTPS id 262F04E414A3; Tue, 1 Sep 2026 14:30:56 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id E35136053C; Tue, 1 Sep 2026 14:30:55 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 62D2C11C79234; Tue, 1 Sep 2026 16:30:41 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1788273049; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=+SEPBPnaaE0LCIqhjI7PwprpKGHWB+21uuj8eFSigLY=; b=NLej3Sc/QvZOoqlMcpCbBhdu5MPiAZEiyD32wu0ObWi0RpuObX21Vsd+l4pT/MZyPt+oP2 Z4G04eoXzCCZPj1TRg0ksHctT86m2HlV6QVDNQJRPqmIfJ3lU/weh8mGvWh63h2aKl0csK a26N1WniKpNa9fmjKC2PWCE2o5VtihHZ0dFChrTd089WE3Xta6cU/A8IS+VJm9h3nsqPSQ XhYw7jUZjjFKiOJoa95TEPjjSPRUrrPYllTwVq8X5Oe6HGJ7HEILUlMqqefqNCGHAaXDXg nyXhnza+eg2J+ut0k6cAW+1JnmnmVNgv/RQdyiGsIDDZ9pxe+e5SoL2aL1Erog== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 01 Sep 2026 16:30:40 +0200 Message-Id: Subject: Re: [PATCH 04/11] drm/panel: merge the drm_kms_helper module into the drm module Cc: "Maarten Lankhorst" , "Thomas Zimmermann" , "David Airlie" , "Simona Vetter" , "Andrzej Hajda" , "Neil Armstrong" , "Robert Foss" , "Laurent Pinchart" , "Jonas Karlman" , "Jernej Skrabec" , "Jessica Zhang" , "Linus Walleij" , "Inki Dae" , "Jagan Teki" , "Marek Szyprowski" , "Dmitry Baryshkov" , "Hui Pu" , "Ian Ray" , "Thomas Petazzoni" , , To: "Luca Ceresoli" , "Maxime Ripard" From: "Luca Ceresoli" X-Mailer: aerc 0.22.0 References: <20260824-cuddly-aardwark-of-reward-0d93d4@houat> In-Reply-To: X-Last-TLS-Session-Version: TLSv1.3 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue Sep 1, 2026 at 2:40 PM CEST, Luca Ceresoli wrote: [...] >>> >> > And we'd essentially move drm_panel_bridge into drm_panel.c, and m= ake it >>> >> > private. >>> >> >>> >> Yes in theory, but the panel_bridge code uses other parts of the >>> >> drm_kms_helper module: drm_atomic_helper and drm_probe_helper, maybe= more, >>> >> so we'd have to move them into the drm module too. >>> > >>> > Ah, right. What would happen if we were doing it the other way around >>> > then? Move drm_panel out of the main drm module? >>> >>> Into the drm_kms_helper module? >>> >>> I had a look and did some experiments and I found at least one user in = the drm >>> module calling a drm_panel API, and guess who: >>> >>> drm_of_find_panel_or_bridge() (in drm_of.c, drm module) >>> -> calls of_drm_find_panel (in drm_panel.c, drm_kms_helper module) >>> >>> Based on our discussion after patch 3, I'm not sure >>> drm_of_find_panel_or_bridge() will disappear soon. If it doesn't, I gue= ss >>> we can try to move drm_of_find_panel_or_bridge() into bridge/panel.c wh= ich >>> is in the drm_kms_helper module (and from drm_of.h info >>> drm_bridge.h?). That however might trigger build failures for drivers w= hich >>> currently don't select DRM_KMS_HELPER and which would have to select it= . >>> >>> I'll give it a try, and if I see major drawbacks I will get back to mov= ing >>> all the drm_kms_helper code into the main drm module. >> >> No, I meant into its own module. > > Looks like a good idea indeed, making the design more modular and > dependencies cleaner. > >> Do we have any dependency from the main >> drm module into drm_panel? > > As far as I can see there is only the one mentioned above: > > drm_of_find_panel_or_bridge() (in drm_of.c, drm module) > -> calls of_drm_find_panel (in drm_panel.c, would-be the new drm_pan= el module) > > And while drm_of_find_panel_or_bridge() is possibly going to disappear at > the end of my series, moving drm_panel.c to its own module would make the > series non-build-bisectable, which would be very annoying. > > However there seem to be no calls from the drm module to > drm_of_find_panel_or_bridge(), so we could move it out as well. What abou= t > a series doing, in this order: > > - move drm_of_find_panel_or_bridge() from the drm module to the > drm_kms_helper module > - move drm_panel.c to a new drm_panel module > - Main change: embed a drm_bridge into every panel > - convert drivers to stop using the panel_bridge, hopefully removing all > calls to drm_of_find_panel_or_bridge() > - remove drm_of_find_panel_or_bridge() Ah, no, that won't work. There would be a circular module dependency loop later on when we embed a drm_bridge into evern drm_panel: indeed at that point drm_panel will use the atomic and probe helpers to implement the embedded drm_bridge, resulting in: * the panel_bridge code in bridge/panel.c [drm_kms_helper module] already depends on the drm_panel.c code (it manipulates a drm_panel, OK) * additionally, the drm_panel.c code, in order to create a drm_bridge, will depend on the helpers in drm_atomic_helper and drm_probe_helper code [drm_kms_helper module] The loop is only between kernel modules (.ko), not in actual code. So I think this revised plan should work (the 2nd bullet is key): - move drm_of_find_panel_or_bridge() from the drm module to bridge/panel.c [currently drm_kms_helper module] - move bridge/panel.o to a new drm_panel_bridge module (NEW) - move drm_panel.c to a new drm_panel module - Main change: embed a drm_bridge into every panel - convert drivers to stop using the panel_bridge, hopefully removing all calls to drm_of_find_panel_or_bridge() - remove drm_of_find_panel_or_bridge() and all the drm_panel_bridge module What do you think about it? Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com