From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay5-d.mail.gandi.net (relay5-d.mail.gandi.net [217.70.183.197]) (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 B3A841B0420; Fri, 7 Feb 2025 08:54:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.70.183.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738918484; cv=none; b=uMvbG7RLtl9lYr8xfcoNCaNUds2SP2vHqWkbcLQ9EgToBwyxJsB0rSotW/0DxSpLiJdGdWf5Hst5XfiyxiFGMi3CW2wyTcV1v7e9LWZzRCu1rGl3PDobgVF/jsnWhunpyQKMIbR+IZQBsPk00PIClOOCo12O7ZeB3NXPWk4FTv4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738918484; c=relaxed/simple; bh=8AUVapBfJ+dKFt4S4I3xRiOQpU+SfNOYrHYg76dXSVM=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=P2qFtTwb0OG11ZTHHU2/th9KedEMIb5nxSBJ0SQtiJqsSVN/rlYP/cVMwOg9SojE29NsHw8Gv7/XPdOkJgDeoaKfEH2yqkbGfS30wfVHs2NcXGu5YjpobN3ZHLvnNlNDVyUvHziJYB9Q5g2ztA6Zxcz27K7oWLRNXlIZbQov3k0= 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=IMbX3HWe; arc=none smtp.client-ip=217.70.183.197 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="IMbX3HWe" Received: by mail.gandi.net (Postfix) with ESMTPSA id D3C65443A5; Fri, 7 Feb 2025 08:54:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=gm1; t=1738918474; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wn7hxWkM/cWBO7IgNnUs/y74YeSzIcIWM0x5ZDLkpdk=; b=IMbX3HWevbzexCXvLrDPdCGV4DgqsZikJxEUhZloTqBXMrb7K5iBqUZzsswJsec98HBthn tP4V8cASf0MG5GOAVmfB0so2WYFTXSwYTb6FfAQTNwgXqzUfqXTWdcjGuzIawsP2FaCedv 4rBDaTsXH9EYzmPHV21Zf0T6c1mC482iupiejkS0t+LLhdXxA0nmme0t7ZcMSCtahBBKCi s4iX7aHyI+gTPDWBaJBWGJcVxPnFomj9RcbuSVw+ocSbDiiReNMvBiIWYkMMsotEZWnNd1 dFxmwaQRSxvzt/z1Hi/mtOcNnRYXPFxVWTv/HhjJn35KZSHb4QDNXAK9x3KJfw== Date: Fri, 7 Feb 2025 09:54:28 +0100 From: Luca Ceresoli To: Dmitry Baryshkov Cc: Simona Vetter , Inki Dae , Jagan Teki , Marek Szyprowski , Catalin Marinas , Will Deacon , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Daniel Thompson , Andrzej Hajda , Jonathan Corbet , Sam Ravnborg , Boris Brezillon , Nicolas Ferre , Alexandre Belloni , Claudiu Beznea , Jessica Zhang , Paul Kocialkowski , Maxime Ripard , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Maarten Lankhorst , Thomas Zimmermann , David Airlie , =?UTF-8?Q?Herv?= =?UTF-8?Q?=C3=A9?= Codina , Thomas Petazzoni , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Paul Kocialkowski Subject: Re: [PATCH v6 08/26] drm/bridge: panel: add a panel_bridge to every panel Message-ID: <20250207095428.244f0f91@booty> In-Reply-To: References: <20250206-hotplug-drm-bridge-v6-0-9d6f2c9c3058@bootlin.com> <20250206-hotplug-drm-bridge-v6-8-9d6f2c9c3058@bootlin.com> Organization: Bootlin X-Mailer: Claws Mail 4.0.0 (GTK+ 3.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-GND-State: clean X-GND-Score: -100 X-GND-Cause: gggruggvucftvghtrhhoucdtuddrgeefvddrtddtgddvkeekgecutefuodetggdotefrodftvfcurfhrohhfihhlvgemucfitefpfffkpdcuggftfghnshhusghstghrihgsvgenuceurghilhhouhhtmecufedtudenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujfgurhepfffhvfevuffkjghfohfogggtgfesthejredtredtvdenucfhrhhomhepnfhutggrucevvghrvghsohhlihcuoehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmqeenucggtffrrghtthgvrhhnpeeglefffefghefhtddvfeeufeeiveekgffgleekieduteekkeetvdehudekgfdvvdenucffohhmrghinhepsghoohhtlhhinhdrtghomhenucfkphepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegtvgejvgemiegtgegvmeeitggtjeemleekgeejnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehinhgvthepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegtvgejvgemiegtgegvmeeitggtjeemleekgeejpdhhvghlohepsghoohhthidpmhgrihhlfhhrohhmpehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmpdhnsggprhgtphhtthhopeefjedprhgtphhtthhopegumhhithhrhidrsggrrhihshhhkhhovheslhhinhgrrhhordhorhhgpdhrtghpthhtohepshhimhhonhgrsehffhiflhhlrdgthhdprhgtphhtthhopehinhhkihdruggrvgesshgrmhhsuhhnghdrt ghomhdprhgtphhtthhopehjrghgrghnsegrmhgrrhhulhgrshholhhuthhiohhnshdrtghomhdprhgtphhtthhopehmrdhsiiihphhrohifshhkihesshgrmhhsuhhnghdrtghomhdprhgtphhtthhopegtrghtrghlihhnrdhmrghrihhnrghssegrrhhmrdgtohhmpdhrtghpthhtohepfihilhhlsehkvghrnhgvlhdrohhrghdprhgtphhtthhopehshhgrfihnghhuoheskhgvrhhnvghlrdhorhhg X-GND-Sasl: luca.ceresoli@bootlin.com On Fri, 7 Feb 2025 04:49:21 +0200 Dmitry Baryshkov wrote: > On Thu, Feb 06, 2025 at 07:14:23PM +0100, Luca Ceresoli wrote: > > Adding a panel does currently not add a panel_bridge wrapping it. Usually > > the panel_bridge creation happens when some other driver (e.g. the previous > > bridge or the encoder) calls *_of_get_bridge() and the following element in > > the pipeline is a panel. > > > > This has some drawbacks: > > > > * the panel_bridge is not created in the context of the driver of the > > underlying physical device (the panel driver), but of some other driver > > * that "other driver" is not aware of whether the returned drm_bridge > > pointer is a panel_bridge created on the fly, a pre-existing > > panel_bridge or a non-panel bridge > > * removal of a panel_bridge requires calling drm_panel_bridge_remove(), > > but the "other driver" doesn't know whether this is needed because it > > doesn't know whether it has created a panel_bridge or not > > > > So far this approach has been working because devm and drmm ensure the > > panel bridge would be dealloacted at some later point. However with the > > upcoming implementation of dynamic bridge lifetime this will get more > > complicated. > > > > Correct removal of a panel_bridge might possibly be obtained by adding more > > devm/drmm technology to have it freed correctly at all times. However this > > would add more complexity and not help making lifetime more understandable. > > > > Use a different approach instead: always create a panel_bridge with a > > drm_panel, thus matching the lifetime of the drm_panel and the panel_bridge > > wrapping it. This makes lifetime much more straightforward to understand > > and to further develop on. > > > > With the panel_bridge always created, the functions to get a bridge > > [devm_drm_of_get_bridge() and drmm_of_get_bridge()] become simpler because > > the bridge they are looking for exists already (if it can exist at all). In > > turn, this is implemented based on a variant of > > drm_of_find_panel_or_bridge() that only looks for panels: > > of_drm_find_bridge_by_endpoint(). In the future > > drm_of_find_panel_or_bridge() can be progressively removed because there > > will never be a panel not exposing a bridge. > > > > Signed-off-by: Luca Ceresoli > > > > --- > > > > This patch was added in v6. > > --- > > drivers/gpu/drm/bridge/panel.c | 74 +++++++++++++++++++++++++++++++++--------- > > include/drm/drm_panel.h | 8 +++++ > > 2 files changed, 66 insertions(+), 16 deletions(-) > > > > LGTM, minor issue below. > > > @@ -1018,6 +1067,11 @@ struct drm_bridge *devm_drm_panel_bridge_add_typed(struct device *dev, > > { > > struct drm_bridge **ptr, *bridge; > > > > + if (panel->bridge) { > > + DRM_DEBUG("panel %s: returning existing bridge=%p", dev_name(dev), panel->bridge); > > + return panel->bridge; > > + } > > Shouldn't the rest of the function also be removed as you do in other > cases? Indeed it should. And even more, I now realize drm_panel_bridge_add_typed() should also become a simple 'return panel->bridge', like its devm and drmm variants, and its code, implementing the actual creation of a panel bridge, move to an internal function. Otherwise this patch is a bug: existing drivers which do call drm_panel_bridge_add_typed() would end up in having two panel_bridges for the same panel. I must say the process of developing this patch together with the hotplug work was "convoluted" to say the least, which probably explains why this got unnoticed so far. Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com