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 8945FCD8CA4 for ; Tue, 9 Jun 2026 10:11:05 +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:References:Cc: Subject:From:To:Message-Id:Date:Content-Type:Content-Transfer-Encoding: Mime-Version:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2wKmJGWh+F/mw2sMZdDF/3ANgln0RLhLSsGBS838lO4=; b=lHDDkX0A9YfbNjC7HQ+vO0v/yv lyBhsFo7mA7SX1JoISaOBpyd3dL1LkbwkznBp9uyR2ciEyVFYMhCt4mgI17eim+BS8vozI/f8mJUZ pINraUBG5B7c2KW9vFCdbKACl8hWp20bVcV4gxDgwCLjVpRIR3sJUP5/yhvAlTNPgQonXDl165m6K aRgkc2E1cfNicesfxArRzUf+UpouXcsWdT9x1dDuMzEmFLTRSduzblW3bsz8XZIoryHmlSJ5LEXZw uQjfyc+Jqlrx2YRgFG34VUZhtL03O+x74QfxaSsU+v/+yS5lNAUgCGSqvMiBEXSFCkbmgkBDi0DsY YFjUV8FQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wWtQA-00000005J6Y-064n; Tue, 09 Jun 2026 10:10:58 +0000 Received: from smtpout-04.galae.net ([185.171.202.116]) by bombadil.infradead.org with esmtps (Exim 4.99.1 #2 (Red Hat Linux)) id 1wWtQ6-00000005J5b-1snj for linux-arm-kernel@lists.infradead.org; Tue, 09 Jun 2026 10:10:56 +0000 Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-04.galae.net (Postfix) with ESMTPS id 960D1C6344C; Tue, 9 Jun 2026 10:10:52 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 101935FFC1; Tue, 9 Jun 2026 10:10:51 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 0C1C3106A2B16; Tue, 9 Jun 2026 12:10:39 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1780999849; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=2wKmJGWh+F/mw2sMZdDF/3ANgln0RLhLSsGBS838lO4=; b=DX9lWzMvivOBeg+GA03lKvb3KNdMdhFWLKfjXhllejwmqUQ7C9eS9CPE8QdPl85nuh0Pue MgMHk8tX/g/lr+tI2K0EuziD0qUqlG+5AmZ+QH20iwZ1Fh9JhI8NqQ9VD+YEND61FFA1F1 1Mt7n9zYGUK9+/yVbkFaN4PaiNcXxhlGv4kOx1Y9xTZ3eMtE7GhZrvpAJzshsRnx6Jg+og n+xVtN9FJYhc1J0E2IbclZzXKCdP3XN6ZA8MAlKhk89H8jqQJjE31Xlb8aPoPpi8lbkSKd R4UhXvPSwRqH0pID4b3q3nj8BSAwvv6e5plzY8znNj9xjnLUx7Ao35jlDQOGKw== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Tue, 09 Jun 2026 12:10:39 +0200 Message-Id: To: "Maxime Ripard" , "Luca Ceresoli" From: "Luca Ceresoli" Subject: Re: [PATCH 23/37] drm/encoder: add drm_encoder_cleanup_from() Cc: "Maarten Lankhorst" , "Thomas Zimmermann" , "David Airlie" , "Simona Vetter" , "Andrzej Hajda" , "Neil Armstrong" , "Robert Foss" , "Laurent Pinchart" , "Jonas Karlman" , "Jernej Skrabec" , "Inki Dae" , "Jagan Teki" , "Marek Szyprowski" , "Marek Vasut" , "Stefan Agner" , "Frank Li" , "Sascha Hauer" , "Pengutronix Kernel Team" , "Fabio Estevam" , "Hui Pu" , "Ian Ray" , "Thomas Petazzoni" , , , , X-Mailer: aerc 0.21.0 References: <20260519-drm-bridge-hotplug-v1-0-45e2bdb3dfb4@bootlin.com> <20260519-drm-bridge-hotplug-v1-23-45e2bdb3dfb4@bootlin.com> <20260608-mighty-woodlouse-of-reading-162bca@houat> In-Reply-To: <20260608-mighty-woodlouse-of-reading-162bca@houat> X-Last-TLS-Session-Version: TLSv1.3 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260609_031054_822338_B8EF45B9 X-CRM114-Status: GOOD ( 23.23 ) 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 Mon Jun 8, 2026 at 2:10 PM CEST, Maxime Ripard wrote: > On Tue, May 19, 2026 at 12:37:40PM +0200, Luca Ceresoli wrote: >> Supporting hardware whose final part of the DRM pipeline can be physical= ly >> removed requires the ability to detach all bridges from a given point to >> the end of the pipeline. >> >> Introduce a variant of drm_encoder_cleanup() for this. >> >> Take care to not try detaching non-attached bridges. This is needed beca= use >> when two or more bridges are removed not in the backwards order, >> drm_encoder_cleanup_from() is called more than once for bridges closer t= o >> the panel. >> >> Signed-off-by: Luca Ceresoli >> >> --- >> >> Note: in theory drm_encoder_cleanup() is now a superset of >> drm_encoder_cleanup_from() and may be simplified to just call >> drm_encoder_cleanup_from() and then do the extra actions. However the >> common code is subtly different in terms of locking and checks, so this >> would complicate the code in this patch and has thus been kept separate = for >> the time being to make reviewing sompler. Reimplementing >> drm_encoder_cleanup() by using drm_encoder_cleanup_from() cvacn be done >> later on. >> >> A much simpler and now obsolete version of this patch (missing locking a= nd >> checks) previously appeared in >> https://lore.kernel.org/lkml/20250206-hotplug-drm-bridge-v6-13-9d6f2c9c3= 058@bootlin.com/ >> --- >> drivers/gpu/drm/drm_encoder.c | 38 ++++++++++++++++++++++++++++++++++++= ++ >> include/drm/drm_encoder.h | 1 + >> 2 files changed, 39 insertions(+) >> >> diff --git a/drivers/gpu/drm/drm_encoder.c b/drivers/gpu/drm/drm_encoder= .c >> index 0d5dbed06db4..40ece477b302 100644 >> --- a/drivers/gpu/drm/drm_encoder.c >> +++ b/drivers/gpu/drm/drm_encoder.c >> @@ -179,6 +179,44 @@ int drm_encoder_init(struct drm_device *dev, >> } >> EXPORT_SYMBOL(drm_encoder_init); >> >> +/** >> + * drm_encoder_cleanup_from - remove a given bridge and all the followi= ng >> + * @encoder: encoder whole list of bridges shall be pruned >> + * @bridge: first bridge to remove >> + * >> + * Removes from an encoder all the bridges starting with a given bridge >> + * and until the end of the chain. >> + * >> + * Does nothing if the bridge is not attached to an encoder chain. >> + * >> + * This should not be used in "normal" DRM pipelines. It is only useful= for >> + * devices whose final part of the DRM chain can be physically removed = and >> + * later reconnected (possibly with different hardware). >> + */ >> +void drm_encoder_cleanup_from(struct drm_encoder *encoder, struct drm_b= ridge *bridge) >> +{ >> + struct drm_bridge *next; >> + LIST_HEAD(tmplist); >> + >> + /* >> + * We need the bridge_chain_mutex to modify the chain, but >> + * drm_bridge_detach() will call DRM_MODESET_LOCK_ALL_BEGIN() (in >> + * drm_modeset_lock_fini()), resulting in a possible ABBA circular >> + * deadlock. Avoid it by first moving all the bridges to a >> + * temporary list holding the lock, and then calling >> + * drm_bridge_detach() without the lock. >> + */ >> + mutex_lock(&encoder->bridge_chain_mutex); >> + if (!list_empty(&bridge->chain_node)) >> + list_for_each_entry_safe_from(bridge, next, &encoder->bridge_chain, c= hain_node) >> + list_move_tail(&bridge->chain_node, &tmplist); >> + mutex_unlock(&encoder->bridge_chain_mutex); >> + >> + while (!list_empty(&tmplist)) >> + drm_bridge_detach(list_first_entry(&tmplist, struct drm_bridge, chain= _node)); >> +} >> +EXPORT_SYMBOL(drm_encoder_cleanup_from); >> + > > The name is super confusing, because it doesn't clean up anything. > drm_encoder_cleanup is called that way because it cleans up the encoder. > This function doesn't. > > Unlike what's being documented, it doesn't remove any bridge either. It > just detaches bridge, so let's just call it that way? Good point. What about: * rename to drm_bridge_detach_from() * drop the @encoder argument (get if from bridge->encoder) * maybe even move to drm_bridge.c? Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com