From nobody Sun Feb 8 21:47:14 2026 Received: from mail-yw1-f201.google.com (mail-yw1-f201.google.com [209.85.128.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9169B1B599 for ; Thu, 22 Feb 2024 03:46:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708573602; cv=none; b=EQ1hMcqPnIG1b97n+WoDXpVqIvCb8/F6mlmE3oCP0SJTX1UtL2gwgUacGYWZf5jwAX4y7TzpiYHKw8frbk4q8M0goND4D8/jVnHyXgKoHtuk8S/Dvw20QZ9EVhL02Ug8CMxgge1JdK4jRTV8mwGUjDUNop4FeyG08GT+Sj9ufZo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1708573602; c=relaxed/simple; bh=cp0XJ1vg7N+tq7T/hQqrmLoRlQ0Tu1sLQF3XCorNNhs=; h=Date:In-Reply-To:Message-Id:Mime-Version:References:Subject:From: To:Cc:Content-Type; b=Eme08yPV1iPSrdNEbpTM0Tl0T9JMs8NuPi+gaBG4B+aXAlbTafNrmqImpfAVoclaJyXrj+8+RoltAeuHdA0wk7eFp6xwSgClhq6dWZn6GB/5pNaW7C5T8wHp49ErRwDu4vda8Ev+Pkm+JDmuh427GKu+Bm98vWlItMUG/OaBVRk= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--saravanak.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=eKdfwIsH; arc=none smtp.client-ip=209.85.128.201 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--saravanak.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="eKdfwIsH" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-602dae507caso122707567b3.0 for ; Wed, 21 Feb 2024 19:46:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1708573598; x=1709178398; darn=vger.kernel.org; h=cc:to:from:subject:references:mime-version:message-id:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=wH33w5aG2BffksVtrB54fX5fBHp+P/Q2DjXoHgc9nyE=; b=eKdfwIsH5w8eFcUFGOrDNG/nCGjXPZf/pnkbbo2V+M9kBdTsxftXqvex1bZH3QyPej vf5qtS1JqXIFAxAKDryQ3FdMVe6Mp+0bq/8FakzEjuZ6Ayub6tPlOUjT267kX4ZXMWe1 OVgbXZVa9Koexehbjaw2ii3FHjPNqATNH3DqUJwaQ7ORk+WovRD8rb/d+jknFyyxFFwA nWq3UA2LLLkKlzygJIKHDrR0Vj5AdeuXqgQvGe7tJ6P0tkyO0ECvctCa/9cKqJQpvFbM 2dAbDJMzfQWssNIDHl5xALh9sYW4wMQ0iiw5i9lvYtzMDQGjc7nG8a5ZB2zfrmHCbW4P mo8Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1708573598; x=1709178398; h=cc:to:from:subject:references:mime-version:message-id:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=wH33w5aG2BffksVtrB54fX5fBHp+P/Q2DjXoHgc9nyE=; b=H622Cml7eW0Wl3kdOmp9FoFgqjMX6U9hjc5jR7pqPvJpGxqO/HdvboOUsKXXZoesA3 SKu//8hfRzwGSLQYYSfFXVe4kqgAeREzbjmXXHZLtLh14y3wP4lV5jwpXZSGXH/QIslK 4FWOpGYP68xZhFHHOQ1diqdWK0GWVD6pji2jkMLY0dgObtJ1T5rWGgw83h2sFSNAP0YD uSrm0jo0UmU2DTDj3ZzbxQHJdclAH9TBasUdPXxQ8fdDFKFVc5S9JCrTCKZDaRXPN2es Kiau4ZWMFX0TS3+T1yLiSf23i6tViyXnpni3JuGiTKa38L7EGwpJcU/Pv6WCsJd+uK/U l6Fg== X-Forwarded-Encrypted: i=1; AJvYcCWnSdDqzyeenTvvc2WCwNpJmDOxuwKWRDEabsH3s15n/G/hxOH8J2IH0c8LnP1FuFiwVq6cgbz4Ag2UIvaqxKWgPbSx1guVrBLqrC0r X-Gm-Message-State: AOJu0Yz9PQeSZ2PFiGfkWVJtEeA5ZL75Q9Ps6hSCMjqY3OalowQL9jEU NVG0Y8HQJxmBKBJU5UPrNKp9KzkU1uFq9mLIz/uJUXar9E5ESrTBfO80pii8p7aDrF5kCRCnNne dO/firH12995lqw== X-Google-Smtp-Source: AGHT+IECAd++kNqbj7P3O+ZaufolEwh1k0tAwEFsFNnN5Q1YIPOlFxgE+MiOrvGczCSWeJaEYcSnAoQ6Lx71cos= X-Received: from saravanak.san.corp.google.com ([2620:15c:2d:3:451c:c6c5:1fb1:a2a1]) (user=saravanak job=sendgmr) by 2002:a25:ef09:0:b0:dc6:53c3:bcbd with SMTP id g9-20020a25ef09000000b00dc653c3bcbdmr325368ybd.7.1708573598675; Wed, 21 Feb 2024 19:46:38 -0800 (PST) Date: Wed, 21 Feb 2024 19:46:21 -0800 In-Reply-To: <20240222034624.2970024-1-saravanak@google.com> Message-Id: <20240222034624.2970024-4-saravanak@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240222034624.2970024-1-saravanak@google.com> X-Mailer: git-send-email 2.44.0.rc0.258.g7320e95886-goog Subject: [PATCH v4 3/4] dt-bindings: Add post-init-providers property From: Saravana Kannan To: Saravana Kannan , Rob Herring , Krzysztof Kozlowski , Conor Dooley , Greg Kroah-Hartman , "Rafael J. Wysocki" , Ard Biesheuvel , Frank Rowand , Andy Shevchenko , Daniel Scally , Heikki Krogerus , Sakari Ailus , Len Brown Cc: kernel-team@android.com, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-efi@vger.kernel.org, linux-acpi@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" The post-init-providers property can be used to break a dependency cycle by marking some provider(s) as a post device initialization provider(s). This allows an OS to do a better job at ordering initialization and suspend/resume of the devices in a dependency cycle. Signed-off-by: Saravana Kannan --- .../bindings/post-init-providers.yaml | 105 ++++++++++++++++++ MAINTAINERS | 13 ++- 2 files changed, 112 insertions(+), 6 deletions(-) create mode 100644 Documentation/devicetree/bindings/post-init-providers.y= aml diff --git a/Documentation/devicetree/bindings/post-init-providers.yaml b/D= ocumentation/devicetree/bindings/post-init-providers.yaml new file mode 100644 index 000000000000..92eb9a027443 --- /dev/null +++ b/Documentation/devicetree/bindings/post-init-providers.yaml @@ -0,0 +1,105 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +# Copyright (c) 2020, Google LLC. All rights reserved. +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/post-init-providers.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Post device initialization providers + +maintainers: + - Saravana Kannan + +description: | + This property is used to indicate that the device(s) pointed to by the + property are not needed for the initialization of the device that lists = this + property. This property does not make a device (that's previously not a + provider) into a provider. It simply downgrades an existing provider to a + post device initialization provider. + + A device can list its providers in devicetree using one or more of the + standard devicetree bindings. By default, it is assumed that the provider + device can be initialized before the consumer device is initialized. + + However, that assumption cannot be made when there are cyclic dependenci= es + between devices. Since each device is a provider (directly or indirectly= ) of + the others in the cycle, there is no guaranteed safe order for initializ= ing + the devices in a cycle. We can try to initialize them in an arbitrary or= der + and eventually successfully initialize all of them, but that doesn't alw= ays + work well. + + For example, say, + * The device tree has the following cyclic dependency X -> Y -> Z -> X (= where + -> denotes "depends on"). + * But X is not needed to fully initialize Z (X might be needed only when= a + specific functionality is requested post initialization). + + If all the other -> are mandatory initialization dependencies, then tryi= ng to + initialize the devices in a loop (or arbitrarily) will always eventually= end + up with the devices being initialized in the order Z, Y and X. + + However, if Y is an optional provider for X (where X provides limited + functionality when Y is not initialized and providing its services), then + trying to initialize the devices in a loop (or arbitrarily) could end up= with + the devices being initialized in the following order: + + * Z, Y and X - All devices provide full functionality + * Z, X and Y - X provides partial functionality + * X, Z and Y - X provides partial functionality + + However, we always want to initialize the devices in the order Z, Y and X + since that provides the full functionality without interruptions. + + One alternate option that might be suggested is to have the driver for X + notice that Y became available at a later point and adjust the functiona= lity + it provides. However, other userspace applications could have started us= ing X + with the limited functionality before Y was available and it might not be + possible to transparently transition X or the users of X to full + functionality while X is in use. + + Similarly, when it comes to suspend (resume) ordering, it's unclear which + device in a dependency cycle needs to be suspended/resumed first and try= ing + arbitrary orders can result in system crashes or instability. + + Explicitly calling out which link in a cycle needs to be broken when + determining the order, simplifies things a lot, improves efficiency, mak= es + the behavior more deterministic and maximizes the functionality that can= be + provided without interruption. + + This property is used to provide this additional information between dev= ices + in a cycle by telling which provider(s) is not needed for initializing t= he + device that lists this property. + + In the example above, Z would list X as a post-init-providers and the + initialization dependency would become X -> Y -> Z -/-> X. So the best o= rder + to initialize them becomes clear: Z, Y and then X. + +select: true + +properties: + post-init-providers: + # One or more providers can be marked as post initialization provider + description: + List of phandles to providers that are not needed for initializing or + resuming this device. + $ref: /schemas/types.yaml#/definitions/phandle-array + items: + maxItems: 1 + +additionalProperties: true + +examples: + - | + gcc: clock-controller@1000 { + compatible =3D "vendor,soc4-gcc", "vendor,soc1-gcc"; + reg =3D <0x1000 0x80>; + clocks =3D <&dispcc 0x1>; + #clock-cells =3D <1>; + post-init-providers =3D <&dispcc>; + }; + dispcc: clock-controller@2000 { + compatible =3D "vendor,soc4-dispcc", "vendor,soc1-dispcc"; + reg =3D <0x2000 0x80>; + clocks =3D <&gcc 0xdd>; + #clock-cells =3D <1>; + }; diff --git a/MAINTAINERS b/MAINTAINERS index 9ed4d3868539..feec740239c9 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -6060,12 +6060,6 @@ S: Maintained F: drivers/base/devcoredump.c F: include/linux/devcoredump.h =20 -DEVICE DEPENDENCY HELPER SCRIPT -M: Saravana Kannan -L: linux-kernel@vger.kernel.org -S: Maintained -F: scripts/dev-needs.sh - DEVICE DIRECT ACCESS (DAX) M: Dan Williams M: Vishal Verma @@ -8300,6 +8294,13 @@ F: include/linux/firewire.h F: include/uapi/linux/firewire*.h F: tools/firewire/ =20 +FIRMWARE DEVICE LINK (fw_devlink) +M: Saravana Kannan +L: linux-kernel@vger.kernel.org +S: Maintained +F: Documentation/devicetree/bindings/post-init-providers.yaml +F: scripts/dev-needs.sh + FIRMWARE FRAMEWORK FOR ARMV8-A M: Sudeep Holla L: linux-arm-kernel@lists.infradead.org (moderated for non-subscribers) --=20 2.44.0.rc0.258.g7320e95886-goog