From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtpout-02.galae.net (smtpout-02.galae.net [185.246.84.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D936E3CCFD8 for ; Tue, 9 Jun 2026 10:10:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=185.246.84.56 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780999854; cv=none; b=Va14Ywpnogdqr1ugsoyM5nUcO/OnEVhz715tvgcGft55LstQ6lRDjDS0+ixFkNism3BwKIm8PYqkDpHM9tLFSr/8nVetOx9wOw0jQWgjSPDjuHmetSZjwtEW5jIiHR2aGnVlTGtLcHG4o5KmIoXZRhCMqVH+u6jUVbkvvrh4VBA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780999854; c=relaxed/simple; bh=CkRz/o0fiewYdn3u7dC6jJbEfZT0Gs4w8ZPCD/ywv8A=; h=Mime-Version:Content-Type:Date:Message-Id:To:From:Subject:Cc: References:In-Reply-To; b=Bd6vfkOhit00rxkI2ip/HwfCxuo2kM+UTKWb+lYDNjxHhhi2ok4WSwxa29nXiqpjwpzn/KizRfWgp8EHVhkig4muwnOCxfwX3YpvTpSOkIbWT8SO/anKBZDl4RQQh9ssuDO6eewpPh4i1O6nJ2sMS/wtrBV+m0x+oD6OE87g5Lc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com; spf=pass smtp.mailfrom=bootlin.com; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b=DX9lWzMv; arc=none smtp.client-ip=185.246.84.56 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=bootlin.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=bootlin.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com header.b="DX9lWzMv" Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-02.galae.net (Postfix) with ESMTPS id 3FF271A37F5; Tue, 9 Jun 2026 10:10:51 +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== Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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 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