From patchwork Sat Feb 10 03:05:46 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Saravana Kannan X-Patchwork-Id: 13552107 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 68E6C1EA73 for ; Sat, 10 Feb 2024 03:06:06 +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=1707534368; cv=none; b=hCOPPOvm0pA9c+F/XRjaz4d6D1g9lF02a3xYVRYnhfhGdDOTgxaAhD/3A06QtmbLTLX/iCWzz34q4yk3yqzOrxOcSVIpkhdolnirA2iC5jIljhZk318FSJvcO2YdnGdzKbnnNHJzyK7rUa7B4SxEEw6vpwmVBozVkSjw3mCcqJc= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707534368; c=relaxed/simple; bh=DDHVFJw3laeMHNAD1vbR4GSUPDGUWbNquUH9HPPVOrQ=; h=Date:In-Reply-To:Message-Id:Mime-Version:References:Subject:From: To:Cc:Content-Type; b=kBDgIC0AcV1Ahy+MIBeF0Yj6oL+/2AA+v8Xvb7ohVUSoKY0vofdaduX/v43H5daODEmBPuuwIryst/9noCtQSIniDvXqw+q/YhSk3+94L2SvMiaWcHtQra4WBHrPfPccbg1x3FXx5L9qr936z01UY3zgwxUWgQeiPdzy+9PYREQ= 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=MmwUDtzn; 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="MmwUDtzn" Received: by mail-yw1-f201.google.com with SMTP id 00721157ae682-604ab15463aso28182947b3.3 for ; Fri, 09 Feb 2024 19:06:06 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1707534365; x=1708139165; 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=EuboiLM3PiYaUht/sxY2s97Ou0aQoJajqakxuwnzARA=; b=MmwUDtznU4pxEV4YFkbbIuvyK8q+MXrRpXGgAtD4vZCbDvQHhZ8VOe8H4NXU/A7iEp k6c7lTUevqRFn/tAlvcZxnv29/YviWAEdZVHZ3sFNj9Svs2WHV1k5oxqZWcCIPOTOx9C 5zEBzpCPUNzTrT3Y1AKjUaceKNe2nREYuB7AtTaBfoRFn8n8aOthXZ+e2vAFOw93n9AQ EZKB5pgOEGDw7rRJMVW3mqrmnCS4181Uv+dJEG9fcodVrroqyZIRy8wjTiF1jPwVEaOf Td3NDLI0u5TQJYZMzrH1cICk97SEVJcELB+Y/2AyYj9HdWF8qZ4fa9FNnPh8ZHw8iQGl Avqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1707534365; x=1708139165; 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=EuboiLM3PiYaUht/sxY2s97Ou0aQoJajqakxuwnzARA=; b=QADzxFq1Y0T9UFMXyPOVUrt90tc3OhorPp57o83pEdwDWUDZtIJHUbnKEgxcTrJcv1 12fav1peHA8CsaKdVuEgpQaUkAqPnG7ZJfy1mhdIzFJLThoDDibodZYN5rnH6KalKW9h 1yWKpDgkrdPA41zV0gSHgXe5/k+4B44//kTmeRe6LhCKuDmYpbZymWDzyxOGvlR/ohIP YNWayRav69ghtvAIOwRVIHKQYXnh+8QkHPFL0wrkLwmxmGMz85fCfA54vs8c0hVT3HwJ FkD/uSaCTVf7wzpCz6xG3dXPUM/8NQiMcMK/gdUhKof6lwKdyVfdm/qn1vOuFGB20+xV JAvA== X-Gm-Message-State: AOJu0YwXCxmyb/h1hbRUP8rKm00DnMWs/k68ta71+f51Fry8S/0nOeOD a/wnPNGfTjMK+q5NuGwVQ3wIZJ/L1ll1/wQolnnREDRbOZARLNmnNBWDC12zCR0JyizkDoMY8SX 1w4AoKJIDgU03bg== X-Google-Smtp-Source: AGHT+IE/vc7byscSKQlhBHSuEvA98GUKQoY9I3PklaoxpxmeP7d7CBzzkKxMJj2zLKm1tFym5Jaqg+ad29EuZwY= X-Received: from saravanak.san.corp.google.com ([2620:15c:2d:3:6b44:91e7:13e1:5d92]) (user=saravanak job=sendgmr) by 2002:a05:690c:884:b0:604:d53e:4616 with SMTP id cd4-20020a05690c088400b00604d53e4616mr179243ywb.6.1707534365489; Fri, 09 Feb 2024 19:06:05 -0800 (PST) Date: Fri, 9 Feb 2024 19:05:46 -0800 In-Reply-To: <20240210030549.4048795-1-saravanak@google.com> Message-Id: <20240210030549.4048795-4-saravanak@google.com> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240210030549.4048795-1-saravanak@google.com> X-Mailer: git-send-email 2.43.0.687.g38aa6559b0-goog Subject: [PATCH v1 3/4] dt-bindings: Add post-init-supplier 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 The post-init-supplier property can be used to break a dependency cycle by marking some supplier(s) as a post device initialization supplier(s). This allows the kernel 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-supplier.yaml | 99 +++++++++++++++++++ MAINTAINERS | 3 +- 2 files changed, 101 insertions(+), 1 deletion(-) create mode 100644 Documentation/devicetree/bindings/post-init-supplier.yaml diff --git a/Documentation/devicetree/bindings/post-init-supplier.yaml b/Documentation/devicetree/bindings/post-init-supplier.yaml new file mode 100644 index 000000000000..cf9071ecd06e --- /dev/null +++ b/Documentation/devicetree/bindings/post-init-supplier.yaml @@ -0,0 +1,99 @@ +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) +# Copyright 2018 Linaro Ltd. +%YAML 1.2 +--- +$id: http://devicetree.org/schemas/post-init-supplier.yaml# +$schema: http://devicetree.org/meta-schemas/core.yaml# + +title: Post device initialization supplier + +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. + + A device can list its suppliers in devicetree using one or more of the + standard devicetree bindings. By default, it would be safe to assume the + supplier device can be initialized before the consumer device is initialized. + + However, that assumption cannot be made when there are cyclic dependecies + between devices. Since each device is a supplier (directly or indirectly) of + the others in the cycle, there is no guaranteed safe order for initalizing + the devices in a cycle. We can try to initialize them in an arbitrary order + and eventually successfully initialize all of them, but that doesn't always + 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 if requested post initialization). + + If all the other -> are mandatory initialization dependencies, then trying 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 supplier 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 functionality + it provides. However, other userspace applications could have started using 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 trying + 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, makes + the behavior more deterministic and maximizes the functionality that can be + provided without interruption. + + This property is used to provide this additional information between devices + in a cycle by telling which supplier(s) is not needed for initializing the + device that lists this property. + + In the example above, Z would list X as a post-init-supplier and the + initialization dependency would become X -> Y -> Z -/-> X. So the best order + to initialize them become clear: Z, Y and then X. + +properties: + # A dictionary of DT properties for this binding schema + post-init-supplier: + # One or more suppliers can be marked as post initialization supplier + minItems: 1 + description: + List of phandles to suppliers that are not needed for initializing or + resuming this device. + $ref: /schemas/types.yaml#/definitions/phandle + +examples: + - | + gcc: general-clock-controller@1000 { + compatible = "vendor,soc4-gcc", "vendor,soc1-gcc"; + reg = <0x1000 0x80>; + clocks = <&dispcc 0x1> + #clock-cells = <1>; + post-init-supplier = <&dispcc>; + }; + dispcc: display-clock-controller@2000 { + compatible = "vendor,soc4-dispcc", "vendor,soc1-dispcc"; + reg = <0x2000 0x80>; + clocks = <&gcc 0xdd> + #clock-cells = <1>; + }; diff --git a/MAINTAINERS b/MAINTAINERS index 3dfe7ea25320..40fd498543a5 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -6055,10 +6055,11 @@ S: Maintained F: drivers/base/devcoredump.c F: include/linux/devcoredump.h -DEVICE DEPENDENCY HELPER SCRIPT +FIRMWARE DEVICE LINK (fw_devlink) M: Saravana Kannan L: linux-kernel@vger.kernel.org S: Maintained +F: Documentation/devicetree/bindings/post-init-supplier.yaml F: scripts/dev-needs.sh DEVICE DIRECT ACCESS (DAX)