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bh=u9TG3OmSzS8fUS1eTfStK5VQAKwBeZ4see00hs7EtDk=; b=IsYdCFfoHd/qOi+gYYbWTZx9rAYgOwGSN0Eo0YXJnG9B/edlJPMStRCvc+FLKq4wqI/fPT 1o0tp81lbGpBiMxcF7EkxBNQLTJ4AW8TE1s3h+3Ao+ryG1FR1N7lvwzYWEpMgHLMK1rp98 XLYJTZyxXDkzfobqUvTulr2czf0EOlP64GFNT5AXkWvxB73odvQWCI/huAFffxIc01O/x+ jInLvozRhnoxnrD5dAmxc9jlW2nmyCQlvuE4hqgOHFPF/9cYlCwYazKn2p5pp5dpHdAi5j SFvCWFSAfDRERL7wOxHamZgj6g3QGMXJO/fr/76NFpGY1qnmq1cAlxnaFpAo5A== Date: Mon, 5 May 2025 17:20:27 +0200 From: Luca Ceresoli To: Maxime Ripard Cc: Maarten Lankhorst , Thomas Zimmermann , David Airlie , Simona Vetter , Andrzej Hajda , Neil Armstrong , Robert Foss , Laurent Pinchart , Jonas Karlman , Jernej Skrabec , Jagan Teki , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , Douglas Anderson , Chun-Kuang Hu , Krzysztof Kozlowski , Anusha Srivatsa , Paul Kocialkowski , Dmitry Baryshkov , Hui Pu , Thomas Petazzoni , dri-devel@lists.freedesktop.org, asahi@lists.linux.dev, linux-kernel@vger.kernel.org, chrome-platform@lists.linux.dev, imx@lists.linux.dev, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-amlogic@lists.infradead.org, linux-renesas-soc@vger.kernel.org, platform-driver-x86@vger.kernel.org, linux-samsung-soc@vger.kernel.org, linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org, linux-stm32@st-md-mailman.stormreply.com Subject: Re: [PATCH v2 34/34] drm/bridge: panel: convert to devm_drm_bridge_alloc() API Message-ID: <20250505172027.25af7721@booty> In-Reply-To: <20250505-beneficial-fossa-of-weather-67c676@houat> References: <20250424-drm-bridge-convert-to-alloc-api-v2-0-8f91a404d86b@bootlin.com> <20250424-drm-bridge-convert-to-alloc-api-v2-34-8f91a404d86b@bootlin.com> <20250428-wild-condor-of-defiance-cadf60@houat> <20250428172516.79058e22@booty> <20250505-beneficial-fossa-of-weather-67c676@houat> Organization: Bootlin X-Mailer: Claws Mail 4.3.1 (GTK 3.24.49; x86_64-redhat-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@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: gggruggvucftvghtrhhoucdtuddrgeefvddrtddtgddvkedugeegucetufdoteggodetrfdotffvucfrrhhofhhilhgvmecuifetpfffkfdpucggtfgfnhhsuhgsshgtrhhisggvnecuuegrihhlohhuthemuceftddunecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenucfjughrpeffhffvvefukfgjfhhoofggtgfgsehtjeertdertddvnecuhfhrohhmpefnuhgtrgcuvegvrhgvshholhhiuceolhhutggrrdgtvghrvghsohhlihessghoohhtlhhinhdrtghomheqnecuggftrfgrthhtvghrnheptdeljeejuddvudetffdtudelfedugfduledtueffuedufefgudegkeegtdeihedunecuffhomhgrihhnpehkvghrnhgvlhdrohhrghdpsghoohhtlhhinhdrtghomhenucfkphepvdgrtddvmeeijedtmedvtddvtdemvggrtddumegsvgegudemleehvgejmeefgeefmeeludefvgenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepihhnvghtpedvrgdtvdemieejtdemvddtvddtmegvrgdtudemsggvgedumeelhegvjeemfeegfeemledufegvpdhhvghlohepsghoohhthidpmhgrihhlfhhrohhmpehluhgtrgdrtggvrhgvshholhhisegsohhothhlihhnrdgtohhmpdhnsggprhgtphhtthhopeefkedprhgtphhtthhopehmrhhiphgrrhgusehkvghrnhgvlhdrohhrghdprhgtphhtthhopehmrggrrhhtvghnrdhlrghnkhhhohhrshhtsehlihhnuhigrdhinhhtvghlrdgtohhmpdhrtghpthhto hepthiiihhmmhgvrhhmrghnnhesshhushgvrdguvgdprhgtphhtthhopegrihhrlhhivggusehgmhgrihhlrdgtohhmpdhrtghpthhtohepshhimhhonhgrsehffhiflhhlrdgthhdprhgtphhtthhopegrnhgurhiivghjrdhhrghjuggrsehinhhtvghlrdgtohhmpdhrtghpthhtohepnhgvihhlrdgrrhhmshhtrhhonhhgsehlihhnrghrohdrohhrghdprhgtphhtthhopehrfhhoshhssehkvghrnhgvlhdrohhrgh X-GND-Sasl: luca.ceresoli@bootlin.com On Mon, 5 May 2025 08:23:26 +0200 Maxime Ripard wrote: > On Mon, Apr 28, 2025 at 05:25:16PM +0200, Luca Ceresoli wrote: > > Hi Maxime, > > > > On Mon, 28 Apr 2025 13:39:23 +0200 > > Maxime Ripard wrote: > > > > > On Thu, Apr 24, 2025 at 10:05:49PM +0200, Luca Ceresoli wrote: > > > > This is the new API for allocating DRM bridges. > > > > > > > > The devm lifetime management of this driver is peculiar. The underlying > > > > device for the panel_bridge is the panel, and the devm lifetime is tied the > > > > panel device (panel->dev). However the panel_bridge allocation is not > > > > performed by the panel driver, but rather by a separate entity (typically > > > > the previous bridge in the encoder chain). > > > > > > > > Thus when that separate entoty is destroyed, the panel_bridge is not > > > > removed automatically by devm, so it is rather done explicitly by calling > > > > drm_panel_bridge_remove(). This is the function that does devm_kfree() the > > > > panel_bridge in current code, so update it as well to put the bridge > > > > reference instead. > > > > > > > > Signed-off-by: Luca Ceresoli > > > > > > This looks fine, but we need a TODO entry to clean this up later on, and > > > a comment on devm_drm_put_bridge that this is inherently unsafe and > > > must not be used. > > > > Ah, I see, OK. > > > > Quick draft: > > > > /** > > * devm_drm_put_bridge - Release a bridge reference obtained via devm > > * @dev: device that got the bridge via devm > > * @bridge: pointer to a struct drm_bridge obtained via devm > > * > > * Same as drm_bridge_put() for bridge pointers obtained via devm functions > > * such as devm_drm_bridge_alloc(). > > + * > > + * This function is a temporary workaround and MUST NOT be used. Manual > > + * handling of bridge lifetime is inherently unsafe. > > */ > > That part looks good to me > > > and: > > > > - devm_kfree(panel_bridge->panel->dev, bridge); > > + /* TODO remove this after reworking panel_bridge lifetime */ > > + devm_drm_put_bridge(panel_bridge->panel->dev, bridge); > > } > > > > Does it look good enough? > > That too, but I was talking about an entry in > https://www.kernel.org/doc/html/latest/gpu/todo.html Ah, sure! I queued this for v3, if you have better suggestions don't hesitate to let me know: -----8<----- Remove devm_drm_put_bridge() ---------------------------- Due to how the panel bridge handles the drm_bridge object lifetime, special care must be taken to dispose of the drm_bridge object when the panel_bridge is removed. This is currently managed using devm_drm_put_bridge(), but that is an unsafe, temporary workaround. To fix that, the DRM panel lifetime needs to be reworked. After the rework is done, remove devm_drm_put_bridge() and the TODO in drm_panel_bridge_remove(). Contact: Maxime Ripard , Luca Ceresoli Level: Intermediate -----8<----- Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com